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Renalia hueberi, a new plant from the lower Devonian of Gaspé
Review of Palaeobotany and Palynology, 22 (1976): 19-37 ©Elsevier Scientific Publishing Company, A m s t e r d a m - Printed in The Netherlands
R E N A L I A HUEBERI, A N E W P L A N T F R O M T H E L O W E R D E V O N I A N O F GASPI~
PATRICIA G. GENSEL' Biological Sciences Group, University of Connecticut, Storrs, Conn. (U.S.A.) (Received April 23, 1975; revised version accepted October 7, 1975)
ABSTRACT Gensel, P. G., 1976. Renalia hueberi, a new plant from the Lower Devonian of Gasp~. Rev. Palaeobot. Palynol., 22: 19--37.
A new genus and species, Renalia hueberi, is described from the Battery Point Formation, Gasp~ Sandstone, Quebec. It consists of I mm wide axes, at least 11 cm long, bearing dichotomous lateral branches terminated by round to reniform sporangia. The sporangia dehisce along the distal margin and the line of dehiscence is bordered by thick-walled, rectangular cells. Spores are trilete, curvaturate and smooth to granulose. Renalia hueberi is superficially similar to the genus Cooksonia, but it differs from the presently known cooksonias in having both pseudomonopodial branching and dehiscent sporangia. It is interpreted however as being evolved from Cooksonia-like plants, and exhibits a sporangial position most comparable to that of the rhyniophytes and a mode of dehiscence characteristic of zosterophylls. INTRODUCTION T h e coastline o f Gasp6 Bay, Q u e b e c , c o n t a i n s s o m e o f t h e m o s t e x t e n s i v e l y fossiliferous e x p o s u r e s of D e v o n i a n s e d i m e n t s in N o r t h A m e r i c a . T h e first e x p l o r a t i o n s a n d d e s c r i p t i o n s o f p l a n t fossils f r o m this area were m a d e b y Sir J. W. D a w s o n , w h o p u b l i s h e d a series o f r e p o r t s starting in 1859. V e r y little a d d i t i o n a l w o r k w a s carried o u t in Gasp6 until r e c e n t years. S o m e o f the resulting p u b l i c a t i o n s r e d e s c r i b e or clarify certain o f t h e plants originally described by Dawson; for example, Hueber and Banks separated plants i n c l u d e d in D a w s o n ' s Psilophyton princeps into P. princeps and Sawdonia ornata ( H u e b e r and Banks, 1 9 6 7 ; H u e b e r , 1 9 6 8 , 1 9 7 1 ) . A f e w s p e c i m e n s o f D a w s o n ' s P. robustius h a v e also b e e n r e - e x a m i n e d ; o n e is n o w c a l l e d Trimerophyton robustius H o p p i n g ( 1 9 5 6 ) a n d o t h e r less readily i d e n t i f i a b l e ones are r e f e r r e d to Loganophyton b y Kr~iusel a n d W e y l a n d (1961). N e w c o l l e c t i o n s o f plants s t r o n g l y r e s e m b l i n g P. robustius are u n d e r s t u d y a n d are m o r e c o m p a r a b l e t o t h e genus Pertica. N e w p l a n t g e n e r a r e p o r t e d f r o m Gasp6 include Eogaspesiea gracilis ( D a b e r , 1 9 6 0 ) , Crenaticaulis verruculosus (Banks a n d Davis, 1 9 6 8 ) a n d a n e w 'Present address: Botany Department, University of North Carolina, Chapel Hill, N.C. 27514 (U.S.A.)
20 species of Psilophyton (Banks et al., 1975). Undoubtedly many more plants remain to be discovered as extensive weathering and erosion along the coast of Gasp~ Bay expose new lenses of fossil-bearing sediments. This account adds another plant to those known from the Gasp~ flora. It was collected from the Battery Point Formation of the Gasp~ Sandstone on the north shore of Gasp~ Bay and will be described as a new genus and species, ~enalia hueberi Gensel. It is distinctive in possessing certain features of both of the major groups of early land plants, the rhyniophytes and the zosterophylls, and an evaluation of its relationships to these groups will be made. REGIONAL GEOLOGY The outcrop from which the specimens were obtained is part of the Battery Point Formation of the Gasp~ Sandstone Group and is located on the beach below and a few hundred yards west of the gun emplacements at Peninsula Gasp6 {Fort Peninsule) on the north shore of Gasp~ Bay. The locality was discovered and initial collections were made by Dr. F. M. Hueber. Additional collections were made by Gensel. McGregor (1973) summarizes the geological and stratigraphic studies dealing with the Battery Point Formation and the reader is referred to that paper for details. Briefly, the Battery Point Formation is considered, along with the underlying York River Formation, to comprise the Gasp6 Sandstone Group and outcrops on both the north and south shore of Gasp6 Bay (McGerrigle, 1950}. The York River Formation is dated as early Emsian (late Early Devonian) on the basis of diagnostic invertebrate fossils (Boucot et al., 1967). The age of the Battery Point Formation is less precisely known as few invertebrate fossils have been found, but on the basis of spore assemblages, McGregor {1973) notes that the Emsian--Eifelian boundary lies approximately midway through it. The locality at Fort Peninsule is part of the lower Battery Point Formation (D. C. McGregor, pers. comm., 1975} and thus it is Emsian or late Early Devonian in age. MATERIALS AND TECHNIQUES The compressions and impressions of Renalia hueberi are preserved in a medium gray shale. The carbonized axes flake off easily leaving only faint impressions, so degaging was of limited value and resulted mainly in an idea of overall morphology and size of the plant. Specimens up to 15 cm in length were macerated in HF and large plant fragments were then removed, washed and mounted on slides. Some of the carbonized fragments obtained from macerations were cleared in Schulze's solution, washed and m o u n t e d on slides. Treatment of cleared axes with dilute base resulted in loss of plant material most of the time, but a few pieces of vascular tissue, exhibiting tracheids, were obtained in this manner. Sporangia were cleared, treated with dilute base and the same procedure repeated until the spores became visible
21
or freed from the sporangium. Spores and plant fragments were examined with a Leitz microscope; some spores were mounted on double-sided Scotch tape, coated with gold-palladium and examined with a Cambridge Stereoscan Mark II scanning electron microscope. DESCRIPTION
Fig.1 is a reconstruction of Renalia hueberi based on whole degaged specimens as well as macerated fragments. The plant consists of main axes which divide more or less equally and on which are borne lateral dichotomous branches terminated by rounded to reniform sporangia. The overall habit of the plant is based on specimens illustrated in Plate I, Plate II, 2 and Plate III, 1, while the location of the lateral branches is a reflection of the variations observed a m o n g hundreds of fragmentary specimens removed from the macerations, including those illustrated in Plates II and Ill. The axes are 0.5--1.5 m m in diameter and lie parallel or nearly so on the rock surface in considerable abundance (Plate I). The longest axis found is 11 c m in length
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Fig.1. R e c o n s t r u c t i o n o f a p o r t i o n o f Renalia hueberi. Scale line equals 5 m m .
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(Plate II, 1) and it is broken at both ends. The basal- and distal-most parts of the plant have n o t been found but examination of several large specimens suggests t h a t the plant may have attained a height of at least 20 cm. The largest upright axes, designated as main axes, are 1--1.5 mm wide. They divide essentially dichotomously at about 4 cm intervals or more (Plate II, 1). Smaller and distinctly laterally positioned dichotomous branches occur at 4-mm to 1-cm intervals along the main axes (Plate II, 2; Plate III, 1, 4). The lateral branch axes range from 0.5 to 0.7 mm wide and from 0.3 to 1.0 cm tall. Most lateral branches divide dichotomously once or twice (Plate II, 7; Plate III, 1--9) and bear 1--4 sporangia. Definitely sterile dichotomous lateral branches were n o t found as branch axes either terminate in sporangia or are broken at the tips (Plate II, 7}. Undivided sterile branches about 1--3 mm long occur on some main axes (Plate II, 6}. Several undivided axis fragments, as well as a few main axes bearing lateral branches, exhibit protuberances of varying size and morphology (Plate II, 3, 4). They range from short, rounded bumps (Plate II, 3, 4) to longer tapered branches (Plate II, 5). Shorter ones exhibit a pad of disorganized tissue at the tip (Plate II, 4). After clearing, all exhibit a darkened central vascular strand which extends nearly to the tip (Plate II, 4, 5). It is suggested that the protuberances represent either aborted or abscised branches (the shorter ones with a pad of tissue) or branches which had n o t completed development before being preserved (the longer ones}. Isolated axes were cleared in an a t t e m p t to examine cellular detail. Cell outlines are faintly visible and suggest that the cells of the axes are elongate and tapered. In one specimen, two parallel thickened cell outlines suggest a stomate, but definitive guard cells were not found. A darkened vascular strand is visible in all cleared axes, lateral branches and protuberances. In regions where the lateral branches depart from main axes, the vascular strand divides below the point of departure of the lateral branch; one part of the strand travels to the branch and the other continues up the main axis (Plate II, 4). The vascular strand reaches almost to the tip of short sterile branches (Plate II, 5} and to the base of sporangia (Plate IV, 3). Axes cleared and then treated with dilute base yielded fragments of tracheids with spiral to scalariform thickenings (Plate IV, 5}. Sporangia are borne terminally on the divisions of lateral branches and are rounded to reniform in shape. They range from 0.75--3.5 mm wide and from 0.75 to 2.5 mm high. The smallest sporangia are more rounded in outline while progressively larger ones are more reniform (Plate IV, 1; Plate III), but all of the sporangia are either equidimensional or broader than tall. The sporangium-bearing axis often flares and extends a short distance into the base of the sporangium (Plate IV, 2). Several specimens were observed in which two sporangia appear to be fused together as if the d i c h o t o m y of the sporangium-bearing axes was never completed but two sporangia developed anyway (Plate III, 5). Many of the sporangia were dehisced at the time of preservation and the line of dehiscence is quite evident. The sporangia open along the distal
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margins into two equal halves (Plate IV, 2, 3). A row of thick-walled, rectangular cells line the margin of both halves (Plate IV, 2--4) while the remainder of the sporangium wall cells are thin-walled and polygonal in outline. Many sporangia still contained spores; a conservative estimate is that several thousand spores ~re produced in a single sporangium (Plate V, 2). The spores removed from sporangia are well-preserved but often obscured by what is interpreted as tapetal material. They are subcircular to circular in equatorial outline and range from 46 to 70/~m in diameter. The triradiate mark is often indistinct but it is simple, and extends about 1/2--3/4 the spore radius. The ends of the trilete rays continue and form a slightly upraised arcuate ridge or curvaturae (Plate V, 1--3) suggesting that the exine may be a little rigid in that region. The curvaturae are located proximal to the equatorial margin and invaginate at the ends of the trilete rays. Occasionally spores are compressed obliquely, so the curvaturae dip below the equatorial margin (Plate V, 1, 3, 5). The exine is 0.3 pm thick, smooth and may have a few sparsely scattered granules. It is unclear whether the granules represent actual sculptural elements or tapetal residue (Plate V, 1, 3, 4). DIAGNOSTIC DATA
Renalia gen. nov. Diagnosis: Plants erect. Main axes divide more or less equally and bear smaller dichotomous lateral branches terminated by round to reniform sporangia. Sporangia dehisce along distal margin. Spores homosporous, trilete. Renalia hueberi sp. nov. Diagnosis: Characters as in generic diagnosis. Main axes 1 - 1 . 5 mm wide and at least 11 cm tall. Lateral branches 1--2 times dichotomous, 0.5--0.8 mm wide and up to 1 cm tall. Protuberances or short sterile branches occur on main axes. Sporangia terminate lateral branches, 0.75--3.5 mm wide and 0.75--2.5 mm tall. Dehiscence occurs along distal margin, line of dehiscence P L A T E II
Renalia hueberi 1. Axis w i t h t w o b i f u r c a t i o n s , G.S.C. 4 3 1 8 0 ; × 1.3. 2. Axis w i t h s p o r a n g i u m - b e a r i n g lateral b r a n c h ; possible s e c o n d lateral b r a n c h o c c u r s above the first. G.S.C. 4 3 1 8 2 1 ; × 5. 3. Axis w i t h p r o t u b e r a n c e s . G.S.C. 4 3 1 8 3 ; x 4.3. 4. Cleared axis s h o w i n g vascular s t r a n d w i t h traces e x t e n d i n g i n t o p r o t u b e r a n c e s . G.S.C. 4 3 1 8 4 ; × 34. 5. S h o r t lateral b r a n c h or possible t e r m i n a t i o n o f axis; vascular s t r a n d e x t e n d s a l m o s t t o tip. G.S.C. 4 3 1 8 5 ; × 12. 6. A sterile lateral b r a n c h , G.S.C. 4 3 1 8 6 ; × 7. 7. Axis w i t h t w o lateral b r a n c h e s , r i g h t o n e w i t h t w o d i c h o t o m i e s . G.S.C. 4 3 1 8 7 ; × 7.
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bordered by row of thick-walled cells. Spores trilete, circular, curvaturate, smooth-minutely granulose, 46--70 pm in diameter• Tracheids with spiralscalariform thickenings. Horizon: Battery Point Formation, Gasp~ Sandstone Group, Emsian (late Early Devonian). Locality: Beach outcrop below gun emplacement at Peninsula Gasp~ (Fort Peninsule) on north shore of Gasp~ Bay, Quebec, Canada. Derivatio nominis: The generic name Renalia is aerived from the latin " t e n " meaning kidney, and the suffix "-alis", meaning iike, in reference to the kidney-hke or remform sporangia. The specific epithet is after Dr. Francis Hueber. Type specimens: Type and illustrated specimens will be deposited in the Geological Survey of Canada collections, Ottawa, Canada. Holotype: G.S.C. 43178, Plate III, 1. Paratypes: G.S.C. 43179, Plate IV, 2; G.S.C. 43180 Plate II, 1. •
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DISCUSSION
Presently, Early Devonian plants are separated into two distinct morphological types: those with terminally borne sporangia are referred to as the Rhynia-type or as rhyniophytes and those with laterally borne sporangia are called the Zosterophyllum-type or zosterophylls. Classification of these plants was established by Banks (1968b) and modified by Banks and Davis (1968), Hueber (1972) and Kasper et ah {1974) and the reader is referred to these publications for further details. Renalia hueberi exhibits a branching pattern and sporangial position most comparable to the rhyniophytes and in terms of sporangial morphology initially resembles the rhyniophyte genus Cooksonia. Close examination however shows that Renalia sporangia dehisce in a manner similar to sporangia of Zosterophyllum (as described by Edwards, 1969), Rebuchia (in Hueber, 1972), and Sawdonia acanthotheca (Gensel et al., 1975), both zosterophylls. This combination of certain morphological features of both rhyniophytes and zosterophylls is observed elsewhere only in a few poorly P L A T E III R e n a l i a hueberi. Axes w i t h fertile lateral b r a n c h e s . 1. G.S.C. 4 3 1 7 8 ; X 5.5. 2. T w o fertile lateral b r a n c h e s o c c u r r i n g close t o g e t h e r , G.S.C. 4 3 1 8 8 ; X 5. 3. G.S.C. 4 3 1 8 9 ; x 6. 4. T w o lateral b r a n c h e s l o c a t e d n e a r l y o p p o s i t e t o o n e a n o t h e r , G.S.C. 4 3 1 9 0 ; X 6. Renalia hueberi. I s o l a t e d lateral b r a n c h e s , s h o w i n g v a r i a t i o n in n u m b e r o f divisions of laterals a n d n u m b e r o f s p o r a n g i a p e r lateral. 5. G.S.C. 4 3 1 9 1 ; x 5.5. 6. G.S.C. 4 3 1 9 2 ; x 7. 7. G.S.C. 4 3 1 9 3 ; x 5. 8. G.S.C. 4 3 1 9 4 ; x 6. 9. G.S.C. 4 3 1 9 5 ; x 6.
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29 understood plants which will be mentioned later. Classification of Renalia and these fragmentary plants is problematical within the existing scheme, and they show that intermediate morphological types exist and suggest that more could possibly be found. The following discussion will first compare Renalia with those r h y n i o p h y t e and zosterophyll genera which exhibit similar features and then postulate its affinities.
Comparison with members o f the Rhyniophyta Renalia hueberi is most similar to the genus Cooksonia and, as will be demonstrated next, appears to have evolved from a Cooksonia-type ancestor. The genus Cooksonia was established by Lang (1937) for plants with dichotomously branched, smooth axes terminated by short, wide sporangia. The axes have elongate, pointed epidermal cells and tracheids with annular thickenings. Lang described t w o species, C. hemisphaerica and C. pertonii, from a number of specimens, none of which is larger than 1.5 cm. Presently there are five generally accepted species of Cooksonia and several plants called Cooksonia sp. or cf. Cooksonia sp. These are mostly based on fragmentary impressions or compressions which range in age from Late Silurian to late Early Devonian (Emsian). The distinctive and unifying feature, and often the only clear-cut aspect of these plants is the essentially rounded, elongate-ovoid, or reniform sporangia and their position at the tips of slender axes. A representative outline drawing of each of the presently known cooksonias (with the exception of those described by Ischenko, 1969), grouped according to their established or estimated geological age, is included in Fig.2. The drawings were made by tracing a figure from a plate of the original publication of each species. Several observations can be made from the chart and certain trends are evident. Late Silurian cooksonias are the oldest known vascular land plants and have been described from Wales, Bohemia, New York State, and Podolia. Cooksonia cf. C. hemisphaerica, described by Obhrel (1962) from the Pridolian of Bohemia, is based on impressions up to 6.5 cm in size and consists of a simple, dichotomizing axis with terminal rounded sporangia (Fig.2A). The sporangia appear to be little more than a swelling of the axis tip. Most of the other Late Silurian cooksonias exhibit the same morphology (Fig.2C--F). However, a specimen described by Obhrel (1962) PLATE IV Renalia hueberi 1. Isolated Renalia sporangia, showing range in shape and size. G.S.C. 43196; × 3.6, 2. Single sporangium, showing distal dehiscence and modified cells along dehiscence line. G.S.C. 43179; × 25. 3. Half of a fertile lateral branch, with two dehisced sporangia. Vascular strand visible to base of sporangia. G.S.C. 43197; × 30. 4. Portion of sporangium wall, showing thick-walled cells along distal edge. G.S.C. 43198; × 120. 5. Cleared axis showing tracheids. G.S.C. 43199; × 200.
31 as ?Cooksonia sp. (Fig.2B) differs in possessing Cooksonia-like sporangia terminating apparently lateral branches. This is therefore the earliest occurrence of a vascular plant which is not strictly dichotomously branched, a feature usually not mentioned in discussions of the architecture of early land plants, probably because of the scanty evidence on which it is based. ?Cooksonia sp. approaches the type of branching pattern seen in Renalia hueberi, but Closer comparison of the two plants is not possible at the present time. Other cooksonias demonstrating dichotomous branching are C. caledonica Edwards (Fig.2G), Cooksonia sp. Banks (Fig.2C), and to some extent the Cooksonia species described by Lang (Fig.2D, F). Some cooksonias are too fragmentary in preservation to determine their branching pattern, such as C. rusanovii Ananiev (Fig.2H), Cooksonia sp. Canright (Fig.2L) and Cooksonia sp. Croft and Lang (Fig.2I). Plants described by Ananiev and Stepanov (1969) from the Lower Devonian of Western Siberia (Siegenian or Emsian) have Cooksonia-like sporangia and are assigned to C. hemisphaerica and C. pertonii. However, they differ from Lang's species in being pseudomonopodially branched or apparently so. The specimens referred to C. hemisphaerica by Ananiev and Stepanov (1969) and illustrated in their plate 1, fig.l, 2 and plate 2, fig.la, could be either one pseudomonopodially branched pl .ant or several more or less dichotomous ones lying close together but at different levels in the matrix (Fig.2J). The plants called C. pertonii and illustrated in plate 2, fig.3--5 of Ananiev and Stepanov (1969) clearly exhibit a main axis and short lateral branches terminated by Cooksonia-type sporangia (Fig.2K). All of these plants are appropriately included in the genus Cooksonia on the basis of their sporangial morphology, even though their branching is not dichotomous. The difference between dichotomous and pseudomonopodial branching is not great and is usually utilized as a character separating species, not genera. For example, some species of Psilophyton are predominantly dichotomous (P. dapsile) while others are pseudomonopodial (P. forbesii, P. microspinosum). However, a more complete understanding of both branching pattern and sporangial morphology is needed to assess the species assignments of the Siberian plants better. It might be noted additionally that the plants referred to C. pertonii by Ananiev and Stepanov (1969) are quite similar in general appearance to Renalia, but as presently known, lack dehiscent sporangia. All of the cooksonias mentioned so far have apparently indehiscent PLATE V Renalia h u e b e r i
1. Light mierograph of two spores, eurvaturae evident. G.S.C. 43200; x 706. 2. Mass of spores within sporangium. G.S.C. 43340; x 200. 3, 4. Scanning electron micrograph of spores, showing narrow, raised eurvaturae, essentially smooth exine, trilete mark. G.S.C. 43341; fig.3 X 1320, fig.4 × 2300. 5. SEM of portion of spore, showing region outside eurvaturae with minute granules representing either ornamentation or tapetal residue. ~" 6300.
32
sporangia which are sometimes little more than a swelling of the branch axis. Lower Devonian cooksonias with sporangia that are more distinct from the axis and which suggest a mode of dehiscence similar to that of Renalia sporangia include C. caledonica Edwards (1970} and C. crassiparietalis Jurina (1964). C. caledonica (Fig.2G) is described as having a thick distal rim, similar to those observed on some compressed Zosterophyllum sporangia, but actual dehiscence along this region could n o t be demonstrated. Some sporangia of C. crassiparietalis (Fig.2M) also possess a rim and are described by Jurina (1964) as dehiscing transversely. However, C. crassiparietalis is based on fragmentary material and sporangial dehiscence is not clearly evident. Further, the overall habit of C. crassiparietalis is not known. If it should possess dehiscent sporangia and pseudo-monopodial branching, it would be very similar to Renalia, differing mainly in the larger size of its sporangia and in spore morphology. Renalia hueberi differs from Cooksonia in being more completely preserved and in having both pseudomonopodial branching and dehiscent sporangia. At the same time, it clearly represents a culmination of certain evolutionary trends seen in cooksonias from the Late Silurian to late Early Devonian times. The oldest cooksonias are mostly dichotomously branched, b u t very early in time developed a more pseudomonopodial habit (?Cooksonia sp. Obhrel). Also, older cooksonias have sporangia which are n o t very distinct from their subtending axes (C. cf. hemisphaerica Obhrel), while younger
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Fig.2. Representative specimens of each known occurrence of Cooksonia (except those described by Ischenko, 1969), plus specimens of Zosterovhyllum artesianum and Renalia hueberi, redrawn from figured specimens as indicated below. All scale lines = 5 mm A--F. Late Silurian cooksonias. A. Cooksonia cf. C. hemispaerica, Bohemia, Obhrel (1962), pl. 1, fig.2. B. ?Cooksonia sp., Bohemia, Obhrel (1962), pl. 2, fig.2. C. Cooksonia sp., New York State, Banks (1974), pl. 1, fig.1. D. C. pertonii, England and Wales, Lang (1937), pl. 8, figs.12, 7. E. Cooksonia sp., Bohemia, Obhrei (1962), pl. 1, fig.5. F. C. hemisphaerica, England and Wales, Lang (1937), pl. 9, fig.33, 32. Cr-O. Lower Devonian cooksonias and closely related genera. G. C. caledonica, Scotland, Edwards (1970), pl. 87, fig.2; text-fig.3. H. Cooksonia rusonovii, Ananiev (1959), pl. 10, fig. 4a. I. Cooksonia sp., Wales, Croft and Lang (1942), pl. 11, fig.43. J. C. hemisphaerica, W. Siberia, Ananiev and Stepanov (1969), pl. 2, fig.1. K. C. pertonii, W. Siberia, Ananiev and Stepanov (1969), pl. 2, fig.4. L. C. cf. C. hemisphaerica, Arizona, Canright (1970), pl. 1, fig.5. M. C. crassiparietalis, Kazakhstan, Jurina (1964), pl. XV, fig.2a, 3b. N. Zosterophyllum artesianum, France, Danz6-Corsin (1956), pl. III, figs.5, 3a. O. Renalia hueberi, Gasp~, Quebec.
34 ones have larger, variously shaped sporangia which are quite distinct from their axes (C. caledonica, Cooksonia species of Ananiev et al.). Some sporangia exhibit a thickened distal rim suggesting possible dehiscence as well. Renalia then is pseudomonopodially branched, with reniform sporangia quite obviously distinct from subtending axes and which dehisce along a region of specialized cells. Other differences between Renalia and Cooksonia species exist in addition to the ones mentioned above. Spores described for C. pertonii by Lang {1937) are small, smooth and possess an equatorial crassitude similar to that seen in the dispersed spore genus Ambitisporites (pers. obs.). Renalia spores are larger and more comparable to the dispersed spore genus Retusotriletes or perhaps a finely ornamented Apiculiretusispora. Also, the tracheids described from C. hemisphaerica axes by Lang (1937) have annular thickenings while those of Renalia are spiral to scalariform. The protuberances observed on Renalia axes are not known among any cooksonias. The closest comparison to them would be the projections observed on stems of Rhynia gwynne-vaughanii (Kidston and Lang, 1917) and they differ in lacking vascular tissue. Other rhyniophyte genera to which Renalia shows some similarity are Hick lingia edwardii Kidston and Lang (1923) and Eogaspesiea gracilis Daber (1960). Hicklingia edwardii was described from the Old Red Sandstone of Scotland by Kidston and Lang from one specimen and consists of a t u f t of smooth axes which divide both dichotomously and pseudomonopodially. Rounded sporangia are borne at the tips of both lateral and terminal branches, presenting an overall habit similar to that of Renalia. Differences in axis size, sporangial shape, lack of sporangial dehiscence and tufted habit distinguish the two genera. Eogaspesiea gracilis Daber is also from the Emsian of Gasp6, but originates from a different locality from that of Renalia. It is much smaller than Renalia, with axes 0.3--0.5 mm in diameter. The axes rarely dichotomize and some are terminated by oval sporangia. Eogaspesiea bears a strong resemblance to the genus Sporogonites and it is doubtful if it is a vascular plant. The tracheids illustrated by Daber (1960) in plate 2, fig.6 were obtained from larger axes which he interpreted as forming a basal rhizome, but which were never demonstrated in connection with the smaller erect axes.
Comparison with members o f the Zosterophyllopsida Plants included in the Zosterophyllopsida possess laterally borne sporangia which are either sessile or terminal on a very short, often recurved stalk. Many zosterophyll sporangia dehisce along the distal margin, forming two equal or unequal sized valves, and sporangia of Zosterophyllum, Rebuchia and Sawdonia acanthotheca hava a rim-like border along the line of dehiscence. Zosterophyllum llanoveranum was re-examined by Edwards (1969) and petrifactions of sporangia demonstrate that the rim corresponds to a region of the sporangium wall that is several cell layers thicker than the
35 remainder of the wall (see Edwards 1969, figs.20--26). Another Early Devonian plant which also possesses reniform, distally dehiscing sporangia is the genus Asteroxylon (sporangia described by Lyon, 1964), a possible precursor to the lycopods. Renalia is similar to zosterophylls mainly in possessing sporangia which dehisce along the distal margin and in possessing a thick distal rim. The evidence obtained from cleared sporangia of Renalia suggests however that the rim is produced by the presence of a row (or possibly rows) of thickerwalled cells, aligned at right angles to the line of dehiscence, rather than a region of increased number of cell layers as was demonstrated by sporangia of Zosterophyllum llanoveranum. Only petrifactions of sporangia of Renalia would clarify this interpretation. But it is evident that the sporangia of some zosterophylls and of Renalia (and possibly those of Asteroxylon) all were evolving approximately similar sorts of dehiscence mechanisms. A plant referred to Zosterophyllum, but differing in several aspects from most species of Zosterophyllurn, is of interest in relation to Renalia. Zosterophyllum artesianum, from the Lower Devonian of R~breuve, France, was described by Danz~-Corsin (1956) as possessing very loose spikes of' reniform sporangia. However, the sporangial arrangement is problematical; none of her plates demonstrate that the sporangia were borne in spikes. Rather, they either illustrate associated, unattached sporangia and axes {plate III, fig.6, Danz6-Corsin, 1956) or reniform sporangia borne at the tips of long axes (plate III, fig.2a, ibid.) reminiscent of the way in which the sporangia of Renalia are borne. Zosterophyllum artesianum sporangia also resemble Renalia sporangia in shape and size and some exhibit a rim along the distal margin. Examination of specimens of Z. artesianum is needed to determine the actual morphology of this plant and its affinities, but as has been previously suggested by Banks (1968a), it could as readily be related to Cooksonia. I suggest further that if the sporangia should be proven to dehisce along the distal margin, it might more appropriately be assigned to the genus Renalia.
Suggested affinities o f Renalia Renalia hueberi offers quite detailed information on the morphology of a simple early land plant. It is most similar to the Rhyniophyta in general appearance, especially Cooksonia, from which it probably evolved. On this basis, Renalia hueberi is classified with the Cooksoniaceae of the Rhyniophyta. It should be emphasized however that Renalia also exhibits a specialized mode of sporangial dehiscence similar in many respects to that found in some members of the Zosterophyllopsida. Tbus, Renalia possesses morphological features intermediate between the two groups of early land plants and in this respect strengthens Banks' suggestion (1968a) that an interrelationship exists between rhyniophytes and zosterophylls. Rhyniophytes at the present time are a poorly, known and heterogeneous group of plants while the zosterophylls are more cohesive in terms of
36
morphology. Intermediates such as Renalia hueberi are difficult to fit into the concept of " r h y n i o p h y t e " or "zosterophyll" as presently established and thus point out the need for, first, finding more plants of Late Silurian and Early Devonian age in order better to understand morphological variation and evolutionary trends among the earliest land plants, and second, eventual modification of the present classification of early land plants when sufficient new information is obtained. ACKNOWLEDGEMENTS
The author expresses her appreciation to Dr. F. M. Hueber and to Dr. H. N. Andrews for the opportunity to carry o u t this study. Financial support for this study was provided by National Science Foundation Grant BMS 7202289 awarded to H. N. Andrews and by the University of Connecticut Research Foundation. Thanks are due to Mary Hubbard, staff artist, for the restoration drawing and illustrations. REFERENCES Ananiev, A. R., 1959. Most Important Localities of Devonian Floras in the Saian-Altai Mountain Region. Tomsk University Publication, Tomsk, (in Russian, Engl. transl.). Ananiev, A. R. and Stepanov, S. A., 1969. The first finding of the Psilophyton flora in the Lower Devonian Salairskij Ridge (Western Siberia). Treatises of the Tomsk Order of the Worker's Red Banner, State University, Tomsk, 2 0 3 : 5 - - 2 8 (in Russian). Banks, H. P., 1968a. The stratigraphic occurrence of early land plants and its bearing on their origin. In: D. H. Oswald (Editor), International Symposium on the Devonian System, 2. Alta. Soc. Pet. Geol., Calgary, pp.721--730. Banks, H. P., 1968b. The early history of land plants. In: E. T. Drake (Editor), Evolution and Environment: A Symposium Presented on the Occasion of the 100th Anniversary of the Peabody Museum of Natural History at Yale University. Yale University Press, New Haven, Conn., pp.73--107. Banks, H. P., 1974. Occurrence of Cooksonia, the oldest vascular land plant macrofossil in the upper Silurian of New York State. J. Indian Bot. Soc. Golden Jubilee Vol., 50A: 227--235. Banks, H. P. and Davis, M. R., 1968. Crenaticaulis, a new genus of Devonian plants allied to Zosterophyllum, and its bearing on the classification of early land plants. Am. J. Bot., 56: 436--449. Banks, H. P., Leclercq, S. and Hueber, F. M., 1975. Anatomy and morphology of Psilophyton dawsonii, sp. n. from the late Lower Devonian of Quebec (Gasp~) and Ontario, Canada. Palaeontogr. Am., 8: 77--127. Boucot, A. J., Cumming, L. M. and Jaeger, H., 1967. Contributions to the age of the Gasp~ Sandstone and Gasp~ Limestone. Geol. Surv. Can. Pap. 6 7 - - 2 5 : 2 2 pp. Canright, J. E., 1970. Spores and associated macrofossils from the Devonian of Arizona. Geosci. Man, 1: 83--88. Croft, W. N. and Lang, W. H., 1942. The lower Devonian flora of the Senni Beds of Monmouthshire and Breconshire. Philos. Trans. R. Soc. Lond., 231: 131--163. Daber, R., 1960. Eogaspesiea gracilis n.g., n. sp. Geologie, 4: 418--425. Danz~-Corsin, P., 1956. Contribution ~ l'~tude des flores d~voniennes du Nord de la France. II. Flore dod~vonienne de R~breuve. Ann. Soc. Gdol. Nord, 76: 24--50. Edwards, D., 1969. Further observations on Zosterophyllum llanoveranum from the Lower Devonian of Wales. Am. J. Bot., 56: 201--210.
37 Edwards, D., 1970. Fertile Rhyniophytina from the Lower Devonian of Britain. Palaeontology, 13(3): 451--461. Gensel, P. G., Andrews, H. N. and Forbes, W. H., 1975. A new species of Sawdonia with notes on the origin of microphylls and lateral sporangia. Bot. Gaz., 136(1): 5 0 - 6 2 . Hopping, C. A., 1956. On a specimen o f Psilophyton robustius from the Lower Devonian o f Canada. Proc. R. Soc. Edinb., 66: 10--28. Hueber, F. M., 1968. Psilophyton: the genus and the concept. In: D. H. Oswald (Editor), International Symposium on the Devonian system, 2. Alta. Soc. Pet. Geol., Calgary, pp.815--822. Hueber, F. M., 1971. Sawdonia ornata: A new name for Psilophyton princeps var. ornatum. Taxon, 20: 641--642. Hueber, F. M , 1972. Rebuchia ovata, its vegetative morphology and classification with the Zosterophyllophytina. Rev. Paleobot. Palynol., 14: 113--127. Hueber, F. M. and Banks, H. P., 1967. Psilophyton princeps: the search for organic connection. Taxon, 16: 81--85. Ischenko, T. A., 1969. Cooksonia paleoflora in the Skala beds of Podolia and its stratigraphic significance. Geol. J., 29: 101--109. Jurina, A. L., 1964. New Devonian species of the genus Cooksonia. Paleontol. Zh., Akad. Nauk. S.S.S.R. (Special Reprint No. 1) pp.107--113 (in Russian). Kasper, A. E., Andrews, H. N. and Forbes, W. H., 1974. New fertile species of Psilophyton from the Devonian of Maine. Am. J. Bot., 61(4): 339--359. Kidston, R. and Lang, W., 1917. On Old Red Sandstone plants showing structure, from the Rhynie Chert Bed, Aberdeenshire. I. Rhynia gwynne-vaughnii, Kidston and Lang. Trans. R. Soc. Edinb., 51(3): 761--784. Kidston, R. and Lang, W., 1923. Notes on fossil plants from the Old Red Sandstone of Scotland. I. Hicklingia edwardi, K. and L. Trans. R. Soc. Edinb., 53(2): 405--407. Kraiisel, R. and Weyland, H., 1961. lJber Psilophyton robustius Dawson. Palaeontographica, Abt. B, 108: 11--21. Lang, W. H., 1937. On the plant-remains from the Downtonian o f England and Wales. Philos. Trans. R. Soc. Lond., B, 227: 245--291. Lyon, A. G., 1964. The probably fertile region of Asteroxylon mackiei K. and L. Nature., 203 (4949): 1082--1083. McGerrigle, H. W., 1950. The geology of eastern Gasp~. Dep. Mines, Que., Geol. Rep. 3 5 : 1 6 9 pp. McGregor, D. C., 1973. Lower and Middle Devonian spores from eastern Gasp~, Canada, I. Systematics. Palaeontographica, Abt. B, 142: 1--77. Obhrel, J., 1962. Die flora der Pridoli-schichten (Budnany-Stufe) des mittelb~hmischen Silurs. Geologie, 1: 83--97.
R E N A L I A HUEBERI, A N E W P L A N T F R O M T H E L O W E R D E V O N I A N O F GASPI~
PATRICIA G. GENSEL' Biological Sciences Group, University of Connecticut, Storrs, Conn. (U.S.A.) (Received April 23, 1975; revised version accepted October 7, 1975)
ABSTRACT Gensel, P. G., 1976. Renalia hueberi, a new plant from the Lower Devonian of Gasp~. Rev. Palaeobot. Palynol., 22: 19--37.
A new genus and species, Renalia hueberi, is described from the Battery Point Formation, Gasp~ Sandstone, Quebec. It consists of I mm wide axes, at least 11 cm long, bearing dichotomous lateral branches terminated by round to reniform sporangia. The sporangia dehisce along the distal margin and the line of dehiscence is bordered by thick-walled, rectangular cells. Spores are trilete, curvaturate and smooth to granulose. Renalia hueberi is superficially similar to the genus Cooksonia, but it differs from the presently known cooksonias in having both pseudomonopodial branching and dehiscent sporangia. It is interpreted however as being evolved from Cooksonia-like plants, and exhibits a sporangial position most comparable to that of the rhyniophytes and a mode of dehiscence characteristic of zosterophylls. INTRODUCTION T h e coastline o f Gasp6 Bay, Q u e b e c , c o n t a i n s s o m e o f t h e m o s t e x t e n s i v e l y fossiliferous e x p o s u r e s of D e v o n i a n s e d i m e n t s in N o r t h A m e r i c a . T h e first e x p l o r a t i o n s a n d d e s c r i p t i o n s o f p l a n t fossils f r o m this area were m a d e b y Sir J. W. D a w s o n , w h o p u b l i s h e d a series o f r e p o r t s starting in 1859. V e r y little a d d i t i o n a l w o r k w a s carried o u t in Gasp6 until r e c e n t years. S o m e o f the resulting p u b l i c a t i o n s r e d e s c r i b e or clarify certain o f t h e plants originally described by Dawson; for example, Hueber and Banks separated plants i n c l u d e d in D a w s o n ' s Psilophyton princeps into P. princeps and Sawdonia ornata ( H u e b e r and Banks, 1 9 6 7 ; H u e b e r , 1 9 6 8 , 1 9 7 1 ) . A f e w s p e c i m e n s o f D a w s o n ' s P. robustius h a v e also b e e n r e - e x a m i n e d ; o n e is n o w c a l l e d Trimerophyton robustius H o p p i n g ( 1 9 5 6 ) a n d o t h e r less readily i d e n t i f i a b l e ones are r e f e r r e d to Loganophyton b y Kr~iusel a n d W e y l a n d (1961). N e w c o l l e c t i o n s o f plants s t r o n g l y r e s e m b l i n g P. robustius are u n d e r s t u d y a n d are m o r e c o m p a r a b l e t o t h e genus Pertica. N e w p l a n t g e n e r a r e p o r t e d f r o m Gasp6 include Eogaspesiea gracilis ( D a b e r , 1 9 6 0 ) , Crenaticaulis verruculosus (Banks a n d Davis, 1 9 6 8 ) a n d a n e w 'Present address: Botany Department, University of North Carolina, Chapel Hill, N.C. 27514 (U.S.A.)
20 species of Psilophyton (Banks et al., 1975). Undoubtedly many more plants remain to be discovered as extensive weathering and erosion along the coast of Gasp~ Bay expose new lenses of fossil-bearing sediments. This account adds another plant to those known from the Gasp~ flora. It was collected from the Battery Point Formation of the Gasp~ Sandstone on the north shore of Gasp~ Bay and will be described as a new genus and species, ~enalia hueberi Gensel. It is distinctive in possessing certain features of both of the major groups of early land plants, the rhyniophytes and the zosterophylls, and an evaluation of its relationships to these groups will be made. REGIONAL GEOLOGY The outcrop from which the specimens were obtained is part of the Battery Point Formation of the Gasp~ Sandstone Group and is located on the beach below and a few hundred yards west of the gun emplacements at Peninsula Gasp6 {Fort Peninsule) on the north shore of Gasp~ Bay. The locality was discovered and initial collections were made by Dr. F. M. Hueber. Additional collections were made by Gensel. McGregor (1973) summarizes the geological and stratigraphic studies dealing with the Battery Point Formation and the reader is referred to that paper for details. Briefly, the Battery Point Formation is considered, along with the underlying York River Formation, to comprise the Gasp6 Sandstone Group and outcrops on both the north and south shore of Gasp6 Bay (McGerrigle, 1950}. The York River Formation is dated as early Emsian (late Early Devonian) on the basis of diagnostic invertebrate fossils (Boucot et al., 1967). The age of the Battery Point Formation is less precisely known as few invertebrate fossils have been found, but on the basis of spore assemblages, McGregor {1973) notes that the Emsian--Eifelian boundary lies approximately midway through it. The locality at Fort Peninsule is part of the lower Battery Point Formation (D. C. McGregor, pers. comm., 1975} and thus it is Emsian or late Early Devonian in age. MATERIALS AND TECHNIQUES The compressions and impressions of Renalia hueberi are preserved in a medium gray shale. The carbonized axes flake off easily leaving only faint impressions, so degaging was of limited value and resulted mainly in an idea of overall morphology and size of the plant. Specimens up to 15 cm in length were macerated in HF and large plant fragments were then removed, washed and mounted on slides. Some of the carbonized fragments obtained from macerations were cleared in Schulze's solution, washed and m o u n t e d on slides. Treatment of cleared axes with dilute base resulted in loss of plant material most of the time, but a few pieces of vascular tissue, exhibiting tracheids, were obtained in this manner. Sporangia were cleared, treated with dilute base and the same procedure repeated until the spores became visible
21
or freed from the sporangium. Spores and plant fragments were examined with a Leitz microscope; some spores were mounted on double-sided Scotch tape, coated with gold-palladium and examined with a Cambridge Stereoscan Mark II scanning electron microscope. DESCRIPTION
Fig.1 is a reconstruction of Renalia hueberi based on whole degaged specimens as well as macerated fragments. The plant consists of main axes which divide more or less equally and on which are borne lateral dichotomous branches terminated by rounded to reniform sporangia. The overall habit of the plant is based on specimens illustrated in Plate I, Plate II, 2 and Plate III, 1, while the location of the lateral branches is a reflection of the variations observed a m o n g hundreds of fragmentary specimens removed from the macerations, including those illustrated in Plates II and Ill. The axes are 0.5--1.5 m m in diameter and lie parallel or nearly so on the rock surface in considerable abundance (Plate I). The longest axis found is 11 c m in length
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Fig.1. R e c o n s t r u c t i o n o f a p o r t i o n o f Renalia hueberi. Scale line equals 5 m m .
23
(Plate II, 1) and it is broken at both ends. The basal- and distal-most parts of the plant have n o t been found but examination of several large specimens suggests t h a t the plant may have attained a height of at least 20 cm. The largest upright axes, designated as main axes, are 1--1.5 mm wide. They divide essentially dichotomously at about 4 cm intervals or more (Plate II, 1). Smaller and distinctly laterally positioned dichotomous branches occur at 4-mm to 1-cm intervals along the main axes (Plate II, 2; Plate III, 1, 4). The lateral branch axes range from 0.5 to 0.7 mm wide and from 0.3 to 1.0 cm tall. Most lateral branches divide dichotomously once or twice (Plate II, 7; Plate III, 1--9) and bear 1--4 sporangia. Definitely sterile dichotomous lateral branches were n o t found as branch axes either terminate in sporangia or are broken at the tips (Plate II, 7}. Undivided sterile branches about 1--3 mm long occur on some main axes (Plate II, 6}. Several undivided axis fragments, as well as a few main axes bearing lateral branches, exhibit protuberances of varying size and morphology (Plate II, 3, 4). They range from short, rounded bumps (Plate II, 3, 4) to longer tapered branches (Plate II, 5). Shorter ones exhibit a pad of disorganized tissue at the tip (Plate II, 4). After clearing, all exhibit a darkened central vascular strand which extends nearly to the tip (Plate II, 4, 5). It is suggested that the protuberances represent either aborted or abscised branches (the shorter ones with a pad of tissue) or branches which had n o t completed development before being preserved (the longer ones}. Isolated axes were cleared in an a t t e m p t to examine cellular detail. Cell outlines are faintly visible and suggest that the cells of the axes are elongate and tapered. In one specimen, two parallel thickened cell outlines suggest a stomate, but definitive guard cells were not found. A darkened vascular strand is visible in all cleared axes, lateral branches and protuberances. In regions where the lateral branches depart from main axes, the vascular strand divides below the point of departure of the lateral branch; one part of the strand travels to the branch and the other continues up the main axis (Plate II, 4). The vascular strand reaches almost to the tip of short sterile branches (Plate II, 5} and to the base of sporangia (Plate IV, 3). Axes cleared and then treated with dilute base yielded fragments of tracheids with spiral to scalariform thickenings (Plate IV, 5}. Sporangia are borne terminally on the divisions of lateral branches and are rounded to reniform in shape. They range from 0.75--3.5 mm wide and from 0.75 to 2.5 mm high. The smallest sporangia are more rounded in outline while progressively larger ones are more reniform (Plate IV, 1; Plate III), but all of the sporangia are either equidimensional or broader than tall. The sporangium-bearing axis often flares and extends a short distance into the base of the sporangium (Plate IV, 2). Several specimens were observed in which two sporangia appear to be fused together as if the d i c h o t o m y of the sporangium-bearing axes was never completed but two sporangia developed anyway (Plate III, 5). Many of the sporangia were dehisced at the time of preservation and the line of dehiscence is quite evident. The sporangia open along the distal
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25
margins into two equal halves (Plate IV, 2, 3). A row of thick-walled, rectangular cells line the margin of both halves (Plate IV, 2--4) while the remainder of the sporangium wall cells are thin-walled and polygonal in outline. Many sporangia still contained spores; a conservative estimate is that several thousand spores ~re produced in a single sporangium (Plate V, 2). The spores removed from sporangia are well-preserved but often obscured by what is interpreted as tapetal material. They are subcircular to circular in equatorial outline and range from 46 to 70/~m in diameter. The triradiate mark is often indistinct but it is simple, and extends about 1/2--3/4 the spore radius. The ends of the trilete rays continue and form a slightly upraised arcuate ridge or curvaturae (Plate V, 1--3) suggesting that the exine may be a little rigid in that region. The curvaturae are located proximal to the equatorial margin and invaginate at the ends of the trilete rays. Occasionally spores are compressed obliquely, so the curvaturae dip below the equatorial margin (Plate V, 1, 3, 5). The exine is 0.3 pm thick, smooth and may have a few sparsely scattered granules. It is unclear whether the granules represent actual sculptural elements or tapetal residue (Plate V, 1, 3, 4). DIAGNOSTIC DATA
Renalia gen. nov. Diagnosis: Plants erect. Main axes divide more or less equally and bear smaller dichotomous lateral branches terminated by round to reniform sporangia. Sporangia dehisce along distal margin. Spores homosporous, trilete. Renalia hueberi sp. nov. Diagnosis: Characters as in generic diagnosis. Main axes 1 - 1 . 5 mm wide and at least 11 cm tall. Lateral branches 1--2 times dichotomous, 0.5--0.8 mm wide and up to 1 cm tall. Protuberances or short sterile branches occur on main axes. Sporangia terminate lateral branches, 0.75--3.5 mm wide and 0.75--2.5 mm tall. Dehiscence occurs along distal margin, line of dehiscence P L A T E II
Renalia hueberi 1. Axis w i t h t w o b i f u r c a t i o n s , G.S.C. 4 3 1 8 0 ; × 1.3. 2. Axis w i t h s p o r a n g i u m - b e a r i n g lateral b r a n c h ; possible s e c o n d lateral b r a n c h o c c u r s above the first. G.S.C. 4 3 1 8 2 1 ; × 5. 3. Axis w i t h p r o t u b e r a n c e s . G.S.C. 4 3 1 8 3 ; x 4.3. 4. Cleared axis s h o w i n g vascular s t r a n d w i t h traces e x t e n d i n g i n t o p r o t u b e r a n c e s . G.S.C. 4 3 1 8 4 ; × 34. 5. S h o r t lateral b r a n c h or possible t e r m i n a t i o n o f axis; vascular s t r a n d e x t e n d s a l m o s t t o tip. G.S.C. 4 3 1 8 5 ; × 12. 6. A sterile lateral b r a n c h , G.S.C. 4 3 1 8 6 ; × 7. 7. Axis w i t h t w o lateral b r a n c h e s , r i g h t o n e w i t h t w o d i c h o t o m i e s . G.S.C. 4 3 1 8 7 ; × 7.
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27
bordered by row of thick-walled cells. Spores trilete, circular, curvaturate, smooth-minutely granulose, 46--70 pm in diameter• Tracheids with spiralscalariform thickenings. Horizon: Battery Point Formation, Gasp~ Sandstone Group, Emsian (late Early Devonian). Locality: Beach outcrop below gun emplacement at Peninsula Gasp~ (Fort Peninsule) on north shore of Gasp~ Bay, Quebec, Canada. Derivatio nominis: The generic name Renalia is aerived from the latin " t e n " meaning kidney, and the suffix "-alis", meaning iike, in reference to the kidney-hke or remform sporangia. The specific epithet is after Dr. Francis Hueber. Type specimens: Type and illustrated specimens will be deposited in the Geological Survey of Canada collections, Ottawa, Canada. Holotype: G.S.C. 43178, Plate III, 1. Paratypes: G.S.C. 43179, Plate IV, 2; G.S.C. 43180 Plate II, 1. •
.
.
DISCUSSION
Presently, Early Devonian plants are separated into two distinct morphological types: those with terminally borne sporangia are referred to as the Rhynia-type or as rhyniophytes and those with laterally borne sporangia are called the Zosterophyllum-type or zosterophylls. Classification of these plants was established by Banks (1968b) and modified by Banks and Davis (1968), Hueber (1972) and Kasper et ah {1974) and the reader is referred to these publications for further details. Renalia hueberi exhibits a branching pattern and sporangial position most comparable to the rhyniophytes and in terms of sporangial morphology initially resembles the rhyniophyte genus Cooksonia. Close examination however shows that Renalia sporangia dehisce in a manner similar to sporangia of Zosterophyllum (as described by Edwards, 1969), Rebuchia (in Hueber, 1972), and Sawdonia acanthotheca (Gensel et al., 1975), both zosterophylls. This combination of certain morphological features of both rhyniophytes and zosterophylls is observed elsewhere only in a few poorly P L A T E III R e n a l i a hueberi. Axes w i t h fertile lateral b r a n c h e s . 1. G.S.C. 4 3 1 7 8 ; X 5.5. 2. T w o fertile lateral b r a n c h e s o c c u r r i n g close t o g e t h e r , G.S.C. 4 3 1 8 8 ; X 5. 3. G.S.C. 4 3 1 8 9 ; x 6. 4. T w o lateral b r a n c h e s l o c a t e d n e a r l y o p p o s i t e t o o n e a n o t h e r , G.S.C. 4 3 1 9 0 ; X 6. Renalia hueberi. I s o l a t e d lateral b r a n c h e s , s h o w i n g v a r i a t i o n in n u m b e r o f divisions of laterals a n d n u m b e r o f s p o r a n g i a p e r lateral. 5. G.S.C. 4 3 1 9 1 ; x 5.5. 6. G.S.C. 4 3 1 9 2 ; x 7. 7. G.S.C. 4 3 1 9 3 ; x 5. 8. G.S.C. 4 3 1 9 4 ; x 6. 9. G.S.C. 4 3 1 9 5 ; x 6.
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29 understood plants which will be mentioned later. Classification of Renalia and these fragmentary plants is problematical within the existing scheme, and they show that intermediate morphological types exist and suggest that more could possibly be found. The following discussion will first compare Renalia with those r h y n i o p h y t e and zosterophyll genera which exhibit similar features and then postulate its affinities.
Comparison with members o f the Rhyniophyta Renalia hueberi is most similar to the genus Cooksonia and, as will be demonstrated next, appears to have evolved from a Cooksonia-type ancestor. The genus Cooksonia was established by Lang (1937) for plants with dichotomously branched, smooth axes terminated by short, wide sporangia. The axes have elongate, pointed epidermal cells and tracheids with annular thickenings. Lang described t w o species, C. hemisphaerica and C. pertonii, from a number of specimens, none of which is larger than 1.5 cm. Presently there are five generally accepted species of Cooksonia and several plants called Cooksonia sp. or cf. Cooksonia sp. These are mostly based on fragmentary impressions or compressions which range in age from Late Silurian to late Early Devonian (Emsian). The distinctive and unifying feature, and often the only clear-cut aspect of these plants is the essentially rounded, elongate-ovoid, or reniform sporangia and their position at the tips of slender axes. A representative outline drawing of each of the presently known cooksonias (with the exception of those described by Ischenko, 1969), grouped according to their established or estimated geological age, is included in Fig.2. The drawings were made by tracing a figure from a plate of the original publication of each species. Several observations can be made from the chart and certain trends are evident. Late Silurian cooksonias are the oldest known vascular land plants and have been described from Wales, Bohemia, New York State, and Podolia. Cooksonia cf. C. hemisphaerica, described by Obhrel (1962) from the Pridolian of Bohemia, is based on impressions up to 6.5 cm in size and consists of a simple, dichotomizing axis with terminal rounded sporangia (Fig.2A). The sporangia appear to be little more than a swelling of the axis tip. Most of the other Late Silurian cooksonias exhibit the same morphology (Fig.2C--F). However, a specimen described by Obhrel (1962) PLATE IV Renalia hueberi 1. Isolated Renalia sporangia, showing range in shape and size. G.S.C. 43196; × 3.6, 2. Single sporangium, showing distal dehiscence and modified cells along dehiscence line. G.S.C. 43179; × 25. 3. Half of a fertile lateral branch, with two dehisced sporangia. Vascular strand visible to base of sporangia. G.S.C. 43197; × 30. 4. Portion of sporangium wall, showing thick-walled cells along distal edge. G.S.C. 43198; × 120. 5. Cleared axis showing tracheids. G.S.C. 43199; × 200.
31 as ?Cooksonia sp. (Fig.2B) differs in possessing Cooksonia-like sporangia terminating apparently lateral branches. This is therefore the earliest occurrence of a vascular plant which is not strictly dichotomously branched, a feature usually not mentioned in discussions of the architecture of early land plants, probably because of the scanty evidence on which it is based. ?Cooksonia sp. approaches the type of branching pattern seen in Renalia hueberi, but Closer comparison of the two plants is not possible at the present time. Other cooksonias demonstrating dichotomous branching are C. caledonica Edwards (Fig.2G), Cooksonia sp. Banks (Fig.2C), and to some extent the Cooksonia species described by Lang (Fig.2D, F). Some cooksonias are too fragmentary in preservation to determine their branching pattern, such as C. rusanovii Ananiev (Fig.2H), Cooksonia sp. Canright (Fig.2L) and Cooksonia sp. Croft and Lang (Fig.2I). Plants described by Ananiev and Stepanov (1969) from the Lower Devonian of Western Siberia (Siegenian or Emsian) have Cooksonia-like sporangia and are assigned to C. hemisphaerica and C. pertonii. However, they differ from Lang's species in being pseudomonopodially branched or apparently so. The specimens referred to C. hemisphaerica by Ananiev and Stepanov (1969) and illustrated in their plate 1, fig.l, 2 and plate 2, fig.la, could be either one pseudomonopodially branched pl .ant or several more or less dichotomous ones lying close together but at different levels in the matrix (Fig.2J). The plants called C. pertonii and illustrated in plate 2, fig.3--5 of Ananiev and Stepanov (1969) clearly exhibit a main axis and short lateral branches terminated by Cooksonia-type sporangia (Fig.2K). All of these plants are appropriately included in the genus Cooksonia on the basis of their sporangial morphology, even though their branching is not dichotomous. The difference between dichotomous and pseudomonopodial branching is not great and is usually utilized as a character separating species, not genera. For example, some species of Psilophyton are predominantly dichotomous (P. dapsile) while others are pseudomonopodial (P. forbesii, P. microspinosum). However, a more complete understanding of both branching pattern and sporangial morphology is needed to assess the species assignments of the Siberian plants better. It might be noted additionally that the plants referred to C. pertonii by Ananiev and Stepanov (1969) are quite similar in general appearance to Renalia, but as presently known, lack dehiscent sporangia. All of the cooksonias mentioned so far have apparently indehiscent PLATE V Renalia h u e b e r i
1. Light mierograph of two spores, eurvaturae evident. G.S.C. 43200; x 706. 2. Mass of spores within sporangium. G.S.C. 43340; x 200. 3, 4. Scanning electron micrograph of spores, showing narrow, raised eurvaturae, essentially smooth exine, trilete mark. G.S.C. 43341; fig.3 X 1320, fig.4 × 2300. 5. SEM of portion of spore, showing region outside eurvaturae with minute granules representing either ornamentation or tapetal residue. ~" 6300.
32
sporangia which are sometimes little more than a swelling of the branch axis. Lower Devonian cooksonias with sporangia that are more distinct from the axis and which suggest a mode of dehiscence similar to that of Renalia sporangia include C. caledonica Edwards (1970} and C. crassiparietalis Jurina (1964). C. caledonica (Fig.2G) is described as having a thick distal rim, similar to those observed on some compressed Zosterophyllum sporangia, but actual dehiscence along this region could n o t be demonstrated. Some sporangia of C. crassiparietalis (Fig.2M) also possess a rim and are described by Jurina (1964) as dehiscing transversely. However, C. crassiparietalis is based on fragmentary material and sporangial dehiscence is not clearly evident. Further, the overall habit of C. crassiparietalis is not known. If it should possess dehiscent sporangia and pseudo-monopodial branching, it would be very similar to Renalia, differing mainly in the larger size of its sporangia and in spore morphology. Renalia hueberi differs from Cooksonia in being more completely preserved and in having both pseudomonopodial branching and dehiscent sporangia. At the same time, it clearly represents a culmination of certain evolutionary trends seen in cooksonias from the Late Silurian to late Early Devonian times. The oldest cooksonias are mostly dichotomously branched, b u t very early in time developed a more pseudomonopodial habit (?Cooksonia sp. Obhrel). Also, older cooksonias have sporangia which are n o t very distinct from their subtending axes (C. cf. hemisphaerica Obhrel), while younger
/ /
j
/
B
\-
A
33
Fig.2. Representative specimens of each known occurrence of Cooksonia (except those described by Ischenko, 1969), plus specimens of Zosterovhyllum artesianum and Renalia hueberi, redrawn from figured specimens as indicated below. All scale lines = 5 mm A--F. Late Silurian cooksonias. A. Cooksonia cf. C. hemispaerica, Bohemia, Obhrel (1962), pl. 1, fig.2. B. ?Cooksonia sp., Bohemia, Obhrel (1962), pl. 2, fig.2. C. Cooksonia sp., New York State, Banks (1974), pl. 1, fig.1. D. C. pertonii, England and Wales, Lang (1937), pl. 8, figs.12, 7. E. Cooksonia sp., Bohemia, Obhrei (1962), pl. 1, fig.5. F. C. hemisphaerica, England and Wales, Lang (1937), pl. 9, fig.33, 32. Cr-O. Lower Devonian cooksonias and closely related genera. G. C. caledonica, Scotland, Edwards (1970), pl. 87, fig.2; text-fig.3. H. Cooksonia rusonovii, Ananiev (1959), pl. 10, fig. 4a. I. Cooksonia sp., Wales, Croft and Lang (1942), pl. 11, fig.43. J. C. hemisphaerica, W. Siberia, Ananiev and Stepanov (1969), pl. 2, fig.1. K. C. pertonii, W. Siberia, Ananiev and Stepanov (1969), pl. 2, fig.4. L. C. cf. C. hemisphaerica, Arizona, Canright (1970), pl. 1, fig.5. M. C. crassiparietalis, Kazakhstan, Jurina (1964), pl. XV, fig.2a, 3b. N. Zosterophyllum artesianum, France, Danz6-Corsin (1956), pl. III, figs.5, 3a. O. Renalia hueberi, Gasp~, Quebec.
34 ones have larger, variously shaped sporangia which are quite distinct from their axes (C. caledonica, Cooksonia species of Ananiev et al.). Some sporangia exhibit a thickened distal rim suggesting possible dehiscence as well. Renalia then is pseudomonopodially branched, with reniform sporangia quite obviously distinct from subtending axes and which dehisce along a region of specialized cells. Other differences between Renalia and Cooksonia species exist in addition to the ones mentioned above. Spores described for C. pertonii by Lang {1937) are small, smooth and possess an equatorial crassitude similar to that seen in the dispersed spore genus Ambitisporites (pers. obs.). Renalia spores are larger and more comparable to the dispersed spore genus Retusotriletes or perhaps a finely ornamented Apiculiretusispora. Also, the tracheids described from C. hemisphaerica axes by Lang (1937) have annular thickenings while those of Renalia are spiral to scalariform. The protuberances observed on Renalia axes are not known among any cooksonias. The closest comparison to them would be the projections observed on stems of Rhynia gwynne-vaughanii (Kidston and Lang, 1917) and they differ in lacking vascular tissue. Other rhyniophyte genera to which Renalia shows some similarity are Hick lingia edwardii Kidston and Lang (1923) and Eogaspesiea gracilis Daber (1960). Hicklingia edwardii was described from the Old Red Sandstone of Scotland by Kidston and Lang from one specimen and consists of a t u f t of smooth axes which divide both dichotomously and pseudomonopodially. Rounded sporangia are borne at the tips of both lateral and terminal branches, presenting an overall habit similar to that of Renalia. Differences in axis size, sporangial shape, lack of sporangial dehiscence and tufted habit distinguish the two genera. Eogaspesiea gracilis Daber is also from the Emsian of Gasp6, but originates from a different locality from that of Renalia. It is much smaller than Renalia, with axes 0.3--0.5 mm in diameter. The axes rarely dichotomize and some are terminated by oval sporangia. Eogaspesiea bears a strong resemblance to the genus Sporogonites and it is doubtful if it is a vascular plant. The tracheids illustrated by Daber (1960) in plate 2, fig.6 were obtained from larger axes which he interpreted as forming a basal rhizome, but which were never demonstrated in connection with the smaller erect axes.
Comparison with members o f the Zosterophyllopsida Plants included in the Zosterophyllopsida possess laterally borne sporangia which are either sessile or terminal on a very short, often recurved stalk. Many zosterophyll sporangia dehisce along the distal margin, forming two equal or unequal sized valves, and sporangia of Zosterophyllum, Rebuchia and Sawdonia acanthotheca hava a rim-like border along the line of dehiscence. Zosterophyllum llanoveranum was re-examined by Edwards (1969) and petrifactions of sporangia demonstrate that the rim corresponds to a region of the sporangium wall that is several cell layers thicker than the
35 remainder of the wall (see Edwards 1969, figs.20--26). Another Early Devonian plant which also possesses reniform, distally dehiscing sporangia is the genus Asteroxylon (sporangia described by Lyon, 1964), a possible precursor to the lycopods. Renalia is similar to zosterophylls mainly in possessing sporangia which dehisce along the distal margin and in possessing a thick distal rim. The evidence obtained from cleared sporangia of Renalia suggests however that the rim is produced by the presence of a row (or possibly rows) of thickerwalled cells, aligned at right angles to the line of dehiscence, rather than a region of increased number of cell layers as was demonstrated by sporangia of Zosterophyllum llanoveranum. Only petrifactions of sporangia of Renalia would clarify this interpretation. But it is evident that the sporangia of some zosterophylls and of Renalia (and possibly those of Asteroxylon) all were evolving approximately similar sorts of dehiscence mechanisms. A plant referred to Zosterophyllum, but differing in several aspects from most species of Zosterophyllurn, is of interest in relation to Renalia. Zosterophyllum artesianum, from the Lower Devonian of R~breuve, France, was described by Danz~-Corsin (1956) as possessing very loose spikes of' reniform sporangia. However, the sporangial arrangement is problematical; none of her plates demonstrate that the sporangia were borne in spikes. Rather, they either illustrate associated, unattached sporangia and axes {plate III, fig.6, Danz6-Corsin, 1956) or reniform sporangia borne at the tips of long axes (plate III, fig.2a, ibid.) reminiscent of the way in which the sporangia of Renalia are borne. Zosterophyllum artesianum sporangia also resemble Renalia sporangia in shape and size and some exhibit a rim along the distal margin. Examination of specimens of Z. artesianum is needed to determine the actual morphology of this plant and its affinities, but as has been previously suggested by Banks (1968a), it could as readily be related to Cooksonia. I suggest further that if the sporangia should be proven to dehisce along the distal margin, it might more appropriately be assigned to the genus Renalia.
Suggested affinities o f Renalia Renalia hueberi offers quite detailed information on the morphology of a simple early land plant. It is most similar to the Rhyniophyta in general appearance, especially Cooksonia, from which it probably evolved. On this basis, Renalia hueberi is classified with the Cooksoniaceae of the Rhyniophyta. It should be emphasized however that Renalia also exhibits a specialized mode of sporangial dehiscence similar in many respects to that found in some members of the Zosterophyllopsida. Tbus, Renalia possesses morphological features intermediate between the two groups of early land plants and in this respect strengthens Banks' suggestion (1968a) that an interrelationship exists between rhyniophytes and zosterophylls. Rhyniophytes at the present time are a poorly, known and heterogeneous group of plants while the zosterophylls are more cohesive in terms of
36
morphology. Intermediates such as Renalia hueberi are difficult to fit into the concept of " r h y n i o p h y t e " or "zosterophyll" as presently established and thus point out the need for, first, finding more plants of Late Silurian and Early Devonian age in order better to understand morphological variation and evolutionary trends among the earliest land plants, and second, eventual modification of the present classification of early land plants when sufficient new information is obtained. ACKNOWLEDGEMENTS
The author expresses her appreciation to Dr. F. M. Hueber and to Dr. H. N. Andrews for the opportunity to carry o u t this study. Financial support for this study was provided by National Science Foundation Grant BMS 7202289 awarded to H. N. Andrews and by the University of Connecticut Research Foundation. Thanks are due to Mary Hubbard, staff artist, for the restoration drawing and illustrations. REFERENCES Ananiev, A. R., 1959. Most Important Localities of Devonian Floras in the Saian-Altai Mountain Region. Tomsk University Publication, Tomsk, (in Russian, Engl. transl.). Ananiev, A. R. and Stepanov, S. A., 1969. The first finding of the Psilophyton flora in the Lower Devonian Salairskij Ridge (Western Siberia). Treatises of the Tomsk Order of the Worker's Red Banner, State University, Tomsk, 2 0 3 : 5 - - 2 8 (in Russian). Banks, H. P., 1968a. The stratigraphic occurrence of early land plants and its bearing on their origin. In: D. H. Oswald (Editor), International Symposium on the Devonian System, 2. Alta. Soc. Pet. Geol., Calgary, pp.721--730. Banks, H. P., 1968b. The early history of land plants. In: E. T. Drake (Editor), Evolution and Environment: A Symposium Presented on the Occasion of the 100th Anniversary of the Peabody Museum of Natural History at Yale University. Yale University Press, New Haven, Conn., pp.73--107. Banks, H. P., 1974. Occurrence of Cooksonia, the oldest vascular land plant macrofossil in the upper Silurian of New York State. J. Indian Bot. Soc. Golden Jubilee Vol., 50A: 227--235. Banks, H. P. and Davis, M. R., 1968. Crenaticaulis, a new genus of Devonian plants allied to Zosterophyllum, and its bearing on the classification of early land plants. Am. J. Bot., 56: 436--449. Banks, H. P., Leclercq, S. and Hueber, F. M., 1975. Anatomy and morphology of Psilophyton dawsonii, sp. n. from the late Lower Devonian of Quebec (Gasp~) and Ontario, Canada. Palaeontogr. Am., 8: 77--127. Boucot, A. J., Cumming, L. M. and Jaeger, H., 1967. Contributions to the age of the Gasp~ Sandstone and Gasp~ Limestone. Geol. Surv. Can. Pap. 6 7 - - 2 5 : 2 2 pp. Canright, J. E., 1970. Spores and associated macrofossils from the Devonian of Arizona. Geosci. Man, 1: 83--88. Croft, W. N. and Lang, W. H., 1942. The lower Devonian flora of the Senni Beds of Monmouthshire and Breconshire. Philos. Trans. R. Soc. Lond., 231: 131--163. Daber, R., 1960. Eogaspesiea gracilis n.g., n. sp. Geologie, 4: 418--425. Danz~-Corsin, P., 1956. Contribution ~ l'~tude des flores d~voniennes du Nord de la France. II. Flore dod~vonienne de R~breuve. Ann. Soc. Gdol. Nord, 76: 24--50. Edwards, D., 1969. Further observations on Zosterophyllum llanoveranum from the Lower Devonian of Wales. Am. J. Bot., 56: 201--210.
37 Edwards, D., 1970. Fertile Rhyniophytina from the Lower Devonian of Britain. Palaeontology, 13(3): 451--461. Gensel, P. G., Andrews, H. N. and Forbes, W. H., 1975. A new species of Sawdonia with notes on the origin of microphylls and lateral sporangia. Bot. Gaz., 136(1): 5 0 - 6 2 . Hopping, C. A., 1956. On a specimen o f Psilophyton robustius from the Lower Devonian o f Canada. Proc. R. Soc. Edinb., 66: 10--28. Hueber, F. M., 1968. Psilophyton: the genus and the concept. In: D. H. Oswald (Editor), International Symposium on the Devonian system, 2. Alta. Soc. Pet. Geol., Calgary, pp.815--822. Hueber, F. M., 1971. Sawdonia ornata: A new name for Psilophyton princeps var. ornatum. Taxon, 20: 641--642. Hueber, F. M , 1972. Rebuchia ovata, its vegetative morphology and classification with the Zosterophyllophytina. Rev. Paleobot. Palynol., 14: 113--127. Hueber, F. M. and Banks, H. P., 1967. Psilophyton princeps: the search for organic connection. Taxon, 16: 81--85. Ischenko, T. A., 1969. Cooksonia paleoflora in the Skala beds of Podolia and its stratigraphic significance. Geol. J., 29: 101--109. Jurina, A. L., 1964. New Devonian species of the genus Cooksonia. Paleontol. Zh., Akad. Nauk. S.S.S.R. (Special Reprint No. 1) pp.107--113 (in Russian). Kasper, A. E., Andrews, H. N. and Forbes, W. H., 1974. New fertile species of Psilophyton from the Devonian of Maine. Am. J. Bot., 61(4): 339--359. Kidston, R. and Lang, W., 1917. On Old Red Sandstone plants showing structure, from the Rhynie Chert Bed, Aberdeenshire. I. Rhynia gwynne-vaughnii, Kidston and Lang. Trans. R. Soc. Edinb., 51(3): 761--784. Kidston, R. and Lang, W., 1923. Notes on fossil plants from the Old Red Sandstone of Scotland. I. Hicklingia edwardi, K. and L. Trans. R. Soc. Edinb., 53(2): 405--407. Kraiisel, R. and Weyland, H., 1961. lJber Psilophyton robustius Dawson. Palaeontographica, Abt. B, 108: 11--21. Lang, W. H., 1937. On the plant-remains from the Downtonian o f England and Wales. Philos. Trans. R. Soc. Lond., B, 227: 245--291. Lyon, A. G., 1964. The probably fertile region of Asteroxylon mackiei K. and L. Nature., 203 (4949): 1082--1083. McGerrigle, H. W., 1950. The geology of eastern Gasp~. Dep. Mines, Que., Geol. Rep. 3 5 : 1 6 9 pp. McGregor, D. C., 1973. Lower and Middle Devonian spores from eastern Gasp~, Canada, I. Systematics. Palaeontographica, Abt. B, 142: 1--77. Obhrel, J., 1962. Die flora der Pridoli-schichten (Budnany-Stufe) des mittelb~hmischen Silurs. Geologie, 1: 83--97.