A review of in situ late Silurian and Devonian spores

Review of Palaeobotany and Palynology, 29 (1980): 253--270

253

© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

A REVIEW OF I N S I T U LATE S I L U R I A N AND DEVONIAN SPORES

K.C. ALLEN

Department of Botany, The University, Bristol BS8 1 UG (Great Britain) (Accepted for publication February 14, 1979)

ABSTRACT Allen, K.C., 1980. A review of in situ Late Silurian and Devonian spores. Rev. Paleobot. Palynol., 29: 253--270. Spores found in sporangia have now been recorded in the literature from sixty Late Silurian and Devonian macroplant species. A review study of these spores, together with an investigation of comparative dispersed spore genera and species, show interesting patterns of construction and sculpture within certain classes.

INTRODUCTION

Much information has been published by palynologists on dispersed spores from rocks of Late Silurian and Devonian age, using them purely as zonal fossils for dating and correllation. In order to identify these dispersed spores, details o f size, shape, sculpture and structure are used to separate them from other specimens, in a binomial classification of form genera and species. Spores found in situ however, have often been described b y palaeobotanists who are more interested in the macroplant construction, and they have often received little detailed attention. However, in the last few years, many more in situ spores have been recorded and described, and this review brings together all published information known to the author on these spores. Many of the earlier records are poorly illustrated and briefly described, and it is hoped at a later date to redescribe these in detailed palynological terms, sectioning the spores where possible. At present, in most cases only the information available in the published literature is used, though comparisons with known dispersed spore genera and species are frequently those of the present writer rather than the original author. Where the affinities of the parent plants are known they are grouped together and mostly tabulated in order to show constructional or sculptural details which may be important and characteristic within that class or grouping.

254 NON-VASCULAR PLANTS Not enough information is available on the in situ spores of non-vascular Late Silurian and Devonian plants to make any generalisations. From the Upper Devonian, Kidston and Lang (1924) recorded spores from Foerstia (Sporocarpon) furcata which are azonate, laevigate, curvaturate, approximately 200 ~m, and can be included within the form genus Retusotriletes. Dispersed Retusotriletes spores of this size are known from the Middle and Upper Devonian. Spores of Lower Devonian and Upper Silurian age from Parka decipiens and Parka sp. (see Lang, 1937, p.258) appear to have a cutinised wall; are azonate and laevigate but show no evidence of a trilete mark. The spores of Parka sp. being smaller (20--30 pm) than those of P. decipiens. Lang (1937) also records azonate laevigate spores (20--45 pm) embedded in the fine tubes of Nematothallus. These may, however, be the dispersed spores of the other macroplants present in these beds. He also records spore-like bodies up to 250 pm in diameter, but in rocks of Downtonian age these are unlikely to be spores. Halle (1916) reported in situ spores from the problematical Sporogonites exuberans from Lower Devonian beds at RSragen, Norway, which appear to be azonate, 20--25 pm and according to Halle (p.27) have a "fine dotted sculpture". Croft and Lang (1942) also report Sporogonites exuberans with in situ spores. These are laevigate, possibly foveolate, azonate and 17.5--25 pm in diameter. A number of simple, spherical atrilete, possibly non-cutinised spores are reported by Kidson and Lang (1921) from possible fungi in the Rhynie Chert. RHYNIOPSIDA

Several Rhyniopsida have been recorded in the literature, with in situ spores. Table I lists these, together with the present writer's interpretation of construction and sculpture from the description and photographs of the original authors. Certain problems arise when trying to make generalisations about the in situ spores of the Rhyniopsida. Many are ill-preserved; and some are possibly immature and may vary in size (Bhutta, 1973b) and sculpture. However, the major problem is the comparison of the three-dimensional petrified spores of Rhynia and Horneophyton with compressed spores, especially when discussing characters such as curvaturae or crassitudes, as for example in the laevigate dispersed spore genera Retusotriletes and Ambitisporites or the apiculate Apiculiretusispora and Aneurospora. Within the Rhyniopsida, all the species found with in situ spores are homosporous, with a spore range within the class of 22.5--77 pro. All the spores are azonate or with a thin crassitude, laevigate or with small cones, grana or spines, and in some instances the azonate spores show evidence of curvaturae. In the Cooksoniaceae apart from C. crassiparietilis and one specimen of Cooksonia in Edwards (1978), all the spores are very small (22.5--37.5 um). These are either laevigate or with minute grana or cones, and azonate or with

255

TABLE

I

In situ spores from

the Rhyniopsida

Parent plant

Author

Spore construction and sculpture

Comparative dispersed spore(s)

Size (~tm)

Age

Cooksonia pertonii

Lang (1937)

laevigate0 s o m e appear azonate and some crassitate

Leiotriletes sp. Arnbitisporites sp.

25--31

L a t e Sil.

C. crassiparietilis

Yttrina (1964)

azonate, partly curvaturate, small grana

APiculiretusispora cf. plicata

50--60

E a r l y Dee.

C. hemisphaeriea

Edwards (1978)

azonate, laevigate

indeterminate

22.5--37.5

L a t e Sil.

Renalia hueberi

Gensel (1976)

azonate, curvatur a t e , l a e v i g a t e or p o s s i b l y w i t h a fine ornament

Retusotriletes sp. o r Apiculiretispora sp.

46--70

E a r l y Dev.

Rhynia gwynnevaughanii

Kidston and Lang (1917, 1919)

azonate, finely apiculate

Granulatisporites sP. Cyclogranisporites sp.

--~ 6 5

E a r l y Dev.

R. gwynnevaughanii

Bhutta (1969)

azonate, finely apiculate, some curvaturate

Granulatisporites cf. 35--50 muninensis Apiculiretusispora sp.

E a r l y Dee.

R. major

Kidston and Lang (1919)

azonate, laevigate

indeterminate

~---6 5

E a r l y Dee.

R. major

Bhutta (1973a)

l a e v i g a t e , o n e specimen with twolayered exine, possibly crassitate

?Ambitisporites sp. (pets. o b s . )

52--78

E a r l y Dee.

Horneophyton lignieri

Kldston and Lang (1919)

azonate, simply apiculate, curvaturate

Apiculiretusispora sp. ~ 5 0

E a r l y Dev.

tt. lignieri

Bhutta (1973b)

curvaturate, simply a p i c u l a t e, s o m e possibly crassitate (pers. o b s . )

Apiculiretusispora sp. 4 2 - - 7 1 ?Emphanisporites decoratus ?Aneurospora sp.

E a r l y Dee.

H. lignieri

Eggert (1974)

azonate, curvaturate, apiculate, some possibly crassitate

Apiculiretusispora sp. 3 9 - - 4 9 ?Aneurospora sp.

E a r l y Dev.

Hostinella globosa

Lang (1925)

azonate, laevigate

cf. Calamospora atava ~ 6 0

Middle Dee.

Salopella allenii

Edwards and Richardson (1974)

azonate, laevigate, curvaturate

indeterminate but possibly Retusotrites

E a r l y Dev.

23--37

256 a slight crassitude. In the Rhyniales, the spores are generally slightly larger, show more definite haptotypic features, and when apiculate, the ornament though small is larger than in Coolesonia. Bhutta (1973a) reported spores from Rhynia major which he assigned to the genus Geminospora. However, they appear to be crassitate and assignable to Ambitisporites. He records these spores as being subreticulate, but this appears to be a preservation character (pers. obs.). Bhutta (1973b) also records specimens assignable to Emphanisporites decoratus Allen in some sporangia of Horneophyton, though these were much less frequent than specimens without proximal radial "ribbing". In looking at Bhutta's specimens, I was not convinced that these are definite haptotypic features, but the result of preservational cracking and possibly some folding. Other spores of H. lignieri appear to have a crassitude rather than curvaturae, and are tentatively assigned to Aneurospora. ZOSTEROPHYLLOPSIDA Seven genera are assigned to this class: namely Zosterophyllum, Rebuchia, Sawdonia, Gosslingia, Nothia, Hicklingia and Crenaticaulis. Of these only the first three are represented by more than one species. Table II shows those species from the five genera from which spores have so far been isolated from the sporangia. The spores are often poorly preserved and the descriptions too short to be certain of their dispersed spore generic assignment. However, there are certain observations which can be made. All the in situ spores appear to be azonate, the exine being of approximately equal thickness throughout. This is an important character, because even in immature spores, the spore construc tion appears not to change with maturity. All the plants are homosporous, with a maximum spore size of 76 ~m. Too few well-documented in situ spores are described to make meaningful comparisons with the Rhyniales, but a possible difference is the lack of any proven crassitude in the Zosterophyllopsida.

ASTER OXYLON MA CKEI Asteroxylon mackei shows characters of both the Zosterophyllopsida and the Lycopsida. Bhutta (1969) records azonate, cingulate spores, with an exine 2--3 ~m thick and a cingulum 5 p m t h i c k , with a size range of 46.2--58.8 pm. He assigns the spores to Aneurospora (?) goensis, but they appear (pers. obs.) to lack sculpture, and have curvaturae rather than a cingulum and are probably assignable to Retusotriletes. LYCOPSIDA Few records of Devonian Lycopsida with in situ spores have been documented, particularly amongst the early herbaceous forms. Spores have not

257 TABLE II In situ spores from the Zosterophyllopsida Parent plant

Author

Spore construction and sculpture

Comparative dispersed spore(s)

Size (~m)

Age

Zosterophyllum llanoveranum

Croft and Lang (1942)

azonate, laevigate

?Leiotriletes sp.

45--65

E a r l y Dev.

Z. llanoveranum

Edwards (1969a)

azonatc, laevigate (exine two layers)

indeterminate

45--59

E a r l y Dev.

Z. m y r e t o nianum

Lang and Cookson (1930)

appears to be azonate, laevigate

indeterminate

25--35

E a r l y Dev.

Lang and

indeterminate

indeterminate

~ 75

Eaxly Dev.

Z. australianum

Cookson, (1930)

Z. cf. fertile

Edwards (1969b)

azonate, exine two-layered at l e a s t in s o m e , c u r v a t u r a t e , laevigate

R e t u s o t r i l e t e s sp.

59--70

E a r l y Dev.

Rebuchia ovata

Hueber (1972)

azonate, laevigate, possibly curvaturate

? R e t u s o t r i l e t e s sp.

68--75

E a r l y Dev.

Goslingia breconensis

Edwards (1970)

azonate, apiculate (small spines and cones)

indeterminate

36--50

E a r l y Dev.

Nothia aphylla

Kidston and Lang (1920)

n o t p o s s i b l e t o see structural or sculptural details

indeterminate

~ 64

E a r l y Dev.

N. a p h y l l a

Bhutta (1969)

azonate, curvaturate, granulate

Apiculiretusispora

58.8--73.5

E a r l y Dev.

N. aphyUa

EI-Saadwy (1966)

azonate, laevigate (no description)

indeterminate

65

E a r l y Dev.

S a w d o n ia ornata

Hueber (1971)

azonate, laevigate

cf. Calamospora 54--64 atava w h i c h is like i n n e r b o d y o f A. brandtii (see McGregor, 1973, p.27)

E a r l y Dev.

Sawdonia acanthotheca

G e n s e l e t al. (1975)

azonate, laevigate, a few curvatttrate, scabrate and a few finely granulate

Calamospora cf. atava R e t u s o t r i l e t e s cf. rotundus ?A p ic ul ire tusispo ra

Middle Dev.

40---76

y e t been identified f r o m Protolepidodendron, Drepanophycus and Colpodexylon, and those from Baragwanathia are indeterminate. Table III shows those Lycopsida so far recorded with in situ spores. Leclercqia complexa needs to be sectioned in order to compare the construction with ot her in situ spores which m a y be assigned to the genus Aneurospora.

258 TABLE III In situ spores from the Lycopsida Parent plant

Author

Spore construction and s c u l p t u r e

Comparative dispersed spore(s)

Size (pm)

Age

Lycopodites oosensis

Krausel and Weyland (1937)

laevigate, b u t it is n o t possible to tell w h e t h e r t h e y are a z o n a t e or w i t h an equatorial feature

indeterminate ( O b r h e l , 1 9 6 1 , says similar to s p o r e s o f Barrendeina dusliana)

90--120

Early Dev.

Baragwanathia longifolia

Lang a n d Cookson (1935)

indeterminate

indeterminate

45-55

? L a t e Sil.

Leclercqia co m p l e x a

Streel ( 1972 )

apiculate, crassitate

A n e u r o s p o r a ef. he terod o n ta

53--92

Middle Dev.

Kristofovichia africani

Nikitin (1934)

megaspores: a z o n a t e , gulate, large spines w i t h b i f u r c a t e tips. microspores: twolayered m o n o l e t e (see M c G r e g o r 1969, p.94)

Nikitinsporites

--500

Archaeoperisaccus

42--45

Late Dev.

Cyclostigma kiltorcense

Chaloner (1968)

megaspores: a z o n a t e , gulate, apiculate; m i c r o spores: n o t k n o w n

Lagenicula

760--1520

L a t e Dev. or earliest Carb.

Barsostrobus famennensis

FaironDemaret (1977)

m e g a s p o r e s : specim e n s d a r k and c a r b o n i s e d ; no i n d i c a t i o n of cons t r u c t i o n ; small v e r r u c a e o n distal surface; smaller spores u n k n o w n

m e g a s p o r e , possibly Trileites

24(}--330

L a t e Dev.

The megaspores in Kristofovichia and Cyclostigma show the apical prominences frequently observed in Carboniferous lycopsid megaspores. Apical prominences appear commonly in late Middle and Late Devonian dispersed megaspores (see Chaloner, 1959; Allen, 1972). It is too early to speculate that most dispersed megaspores in the Devonian with an apical prominence as defined by Allen (1972), are from Lycopsida, but to date no in situ megaspores from other classes show this development. At present the megaspores observed in Barsostrobus famennensis are too poorly preserved to offer comment on their construction. If thick-walled megaspores are preserved in proximo-distal aspect, it is often difficult to see an apical prominence. Chaloner (1959) suggested that the dispersed megaspore Biharisporites ellesmerensis was possibly from a lycopsid, but as shown later in this paper, they are more likely to be from progymnosperms.

259

INCERTAE SEDIS, WITH POSSIBLE LYCOPSID AFFINITIES

Table IV, shows those plants at present classified as Incertae Sedis, but having some characters in common with Lycopsida. TABLE IV

In situ spores of plants here placed in Incertae sedis, which have certain affinities with the

Lycopsida Parent plant

Author

Spore construction and sculpture

Comparative dispersed spore(s)

Protobarinophyton obrutschevii

Nadler (1966)

azonate, laevigate

C a l a m o s p o r a cf. atava

45--63

Early Dev.

P. t i m a n i c u m

Petrosyan (1968)

azonate, laevigate

C a l a m o s p o r a cf. pannucea

70---90

Early Dev.

Krithodeophyton croftii

Edwards (1968)

azonate, curvaturate, finely apiculate

Apiculiretusispora cf. b r a n d t i i

55--68

Early Dev.

Barinophyton citrulliforme

Arnold (1939)

megaspores: azonate laevigate

Calamospora sp.

300--400

Late Dev.

microspores: similar to B. r i c h a r d s o n i i (see Pettitt, 1970)

C a l a m o s p o r a sp

megaspores: azonate laevigate infrapunctate microspores: azonate, laevigate

C a l a m o s p o r a sp.

220---250

Late Dev.

C a l a m o s p o r a cf. pannucea

48--62 97--240

B. r i c h a r d s o n i i

Pettitt (1965)

Barinophyton-Protobarino p h y t o n ty pe plant

Petti tt (1970) Hueber material)

azonate, laevigate,

Calamospora p a n n u e e a and C. sp. of McGregor (1973, p.14, 15)

Enigmophyton superbum

Vigran (1964)

megaspores: laevigate, in frapunctate microspores: laevigate, some cttrvaturate

Enigmophytospora simplex

zonate, apiculate

D e n s o s p o r i t e s sp. S a m a r i s p o r i t e s sp.

Barrandetna dusliana

Obrhel (1961)

Size (~m)

240--290

Age

Early Dev.

Middle Dev.

C a l a m o s p o r a cf. 65--75 pannucea Retusotriletes ro tu nd us

73--100

Middle Dev.

Pettitt (1970) noted that the microspores of Barinophyton citrulliforme, were closely comparable with those from B. richardsonii. He also reported on the in situ spores from a Barinophyton--Protobarinophyton type plant at present being studied by Hueber, in which the large size range for the spores (97--240 um) may hold for each sporangium. These spores span the range for McGregor's {1973) specimens of Calamospora pannucea and C. sp. Vigran

260 (1964) found in situ spores in sporangia associated with, but not attached to, Enigmophyton superbum. Both the mega- and microspores are very similar to those recorded for Barinophyton, and if these are the heterospores of Enigmophyton, it may indicate a close botanical relationship between the two genera. Obrhel (1961) records the in situ spores of Barrandeina dusliana. These he reports as cingulate, likens them to the in situ spores of Lycopodites oosensis Kr~iusel et Weyland 1937, and places them in the dispersed spore genus Lycospora. From his photographs they appear more readily assignable to Densosporites and Samarisporites, with some similarity to certain in situ spores of Oocampsa catheta (Andrews et al., 1975). The in situ spore of B. dusliana illustrated in Obrhel (1961, plate 8, fig.6), looks remarkably like the important zonal spore Samarisporites triangulatus Allen. TRIMEROPHYTOPSIDA There is a tendency particularly within Lower Devonian spores, for the outer sculptured layer to slough off, leaving the unornamented inner part of the exine (see McGregor, 1973; Allen, 1976). This often appears to be the removal of the outer sculptured part of an undivided, but possibly differentially structured exine, rather than the removal of an exoexine leaving the intexine. Consequently, certain specimens of Apiculiretusispora for example, can, when this outer layer is removed, be placed either within the dispersed spore genus Retusotriletes or another azonate laevigate genus, depending on whether the original curvaturae are expressed on the inner part of the exine. When the sculptured layer of Apiculiretusispora brandtii Streel is removed for example, the inner part lacks curvaturae, and would be placed within Calamospora atava (McGregor, 1973, p.13). It is important to remember this when looking at the in situ spores of the trimerophytes where there is evidence of a sloughing off of the outer sculptured layer. There appears to be some similarity amongst the in situ spores of the trimerophytes (Table V). All are azonate and most are curvaturate, and lack the characteristic crassitate thickening of Ambitisporites and Aneurospora. Some specimens are referable to the genera Retusotriletes and Calamospora, but these could represent the inner part of an ornamented exine which has sloughed off. This sculptured layer may be tapetal as suggested by Banks et al. (1975) or exinal as suggested by McGregor (1973) and others. If the sculptured layer was retained, then the spores would be included within the genus Apiculiretusispora. Other in situ trimerophyte spores referable to the genus Apiculiretusispora are also reported but as yet unpublished, by Granhoff et al. (1976 p.126), from several species of Psilophyton and two species of Trimerophyton. They report that spores of Psilophyton resemble A. brantii when the outer layer of the exine is sloughed off, whilst Pertica varia and a new species of Trimerophyton resemble A. arenorugosa and A. plicata.

261 TABLE V In situ spores from the Trimerophytopsida Parent plant

Author

Spore construction and structure

Comparative dispersed spore(s)

Size (Din).

Age

Trimerophyton robustius

Hopping (1956)

azonate, curvaturate, laevigate or with small cones

Apiculiretusispora sp. Retusotriletes sp.

40--63

E a r l y Dev.

Dawsonites arcuatus

Croft and Lang (1942)

azonate, laevigate

Calamospora cf. pannucea

50--85

E a r l y Dev.

cf. D. arcuatus

Hueber (1964)

azonate, curvaturate laevigate (originally apiculate)

Apiculiretusispora sp. (see M c G r e g o r 1973, p.21)

--

E a r l y Dev.

Psilophyton princeps

Lang (1931)

azonate, laevigate

Calarnospora cf. atava Calamospora cf. pannucea

60--100

E a r l y Dev.

P. p r i n c e p s

Hueber (1968)

azonate, curvaturate (when outerlayer preserved), laevigate (originally apiculate)

Calarnospora ef. stays Apiculiretusispora cf. brandtii

75---80

E a r l y Dev. or early Middle Dev.

P. d a w s o n i i

B a n k s e t al, (1975)

azonate, curvaturate, laevigate (originally apiculate)

Retusotriletes cf. r o t u n d u s possibly some Apiculiretusispora sp.

40--75

E a r l y Dev.

Pertica varia

Granhoff et al. (1976)

azonate, curvaturate, apiculate

Apiculiretusispora cf. arenorugosa A. plicata

56--90

E a r l y Dev.

CLADOXYLOPSIDA

Too few representatives of this class have been recorded with in situ spores to make any generalisations regarding spore construction. Bonamo and Banks (1966) recorded the in situ spores of Calamophyton bicephalum from the Middle Devonian, and compared them with the dispersed spore Dibolisporites cf. gibberosus var. major (= D. echinaceus sensu McGregor, 1973). Dibolisporites echinaceus is a c o m m o n and widespread Middle Devonian spore. The only other possible record of in situ cladoxylalean spores is from Pseudosporochnus krejcii (Leclercq, 1940). These are very small, indeterminate, and if the measurements are correct (6--9 ~m) are unlikely to be the spores of this plant.

262 SPHENOPSIDA Only two probable sphenopsids have been recorded with in situ spores. From Hyenia elegans of the Middle Devonian, Leclercq (1940, p.10) reports small round objects only 7--10 ~m in diameter with a small apiculate ornament, resulting from maceration of the sporangia. Unfortunately neither the photographs nor the description give any information on the spore structure or sculpture, and at present they must be recorded as indeterminate. From the Upper Devonian of Belgium, Leclercq (1957) records in situ spores from Eviostachya hoegii. These range in size from 21 to 42 pm and would appear to be azonate, with a variable ornament of cones and spines, the spines are often bifurcate. Leclercq compares them with the dispersed spore genus Acanthotriletes and in particular with A. famennensis Naumova. However, the photographs are not very informative and these interesting spores, particularly the sculptural elements, need further study before making a more definite dispersed spore comparison. PROGYMNOSPERMOPSIDA

Rhabdosporites is a widely distributed dominantly Middle Devonian dispersed spore genus (see Richardson, 1974, p.6). It has a cavity between the exoexine and intexine, and is characterised by having an " o r n a m e n t " of small flat-topped rods. Sometimes, it is n o t clear whether these are a sculptural feature, or due to exinal erosion of an infragranulate structure. Aneurospora does not appear to have a separation of the exine into an exoexine and intexine, and is characterised by having a crassitude or at least some proximoequatorial feature (unlike the dominantly equatorial cingulum). The proximal surface is characteristically more flattened than the distal, and can be separated from Ambitisporites on the presence of an ornament. Geminospora has a two-layered exine, with the intexine often adpressed to the exoexine and therefore difficult to see except in thin section. The distal surface is thicker than the proximal, though this character is not always obvious, and it is laevigate or with an ornament usually of cones, grana or short spines. However, in certain species or specimens of Geminospora, as for example in G. svalbardiae, some spores although having an intexine and exoexine, have a more flattened proximal surface, and often slight development of a crassitude, and could be placed in Aneurospora, whilst others appear intermediate between the two. Some specimens of G. svalbardiae are very similar to Aneurospora greggsii (McGregor) Streel and might well come from related plants. Other specimens of Geminospora in which the intexine is well separated from the exoexine, closely resemble certain species of Rhabdosporites. In material from Fair Isle (pers. obs.) spores which are clearly from the same or related parents, can at one end be placed in Geminospora, and at the other can grade through into R habdosporites. From New York State, Streel (1972) finds spores which he found difficult to place in just one of the genera Rhabdosporites, Aneurospora or Geminospora. It seems likely that some of the species

263 or specimens referable to these three dispersed spore genera are produced by the same or related plants. The genus Biharisporites contains a number of dispersed megaspore species, and is c o m m o n in the late Middle and Late Devonian. They are characterised b y having a variable ornament o f cones, tubercles and biform elements, their bases often anastomosing into an irregular cristo-reticulum. A thin intexinal layer, often referred to as a mesosporium, separates from the exoexine, to a varying extent. Contagisporites also contains a number of megaspore species, with the same type and variation in ornament as Biharisporites. Contagisporites however is characterised b y having either curvatural ridges or folds, and is clearly cavate (camerate) with a more rigid intexine. Biharisporites and Contagisporites often occur in the same samples, and in the author's Greenland material, specimens with identical ornament, which appear to be from the same or related parent plants, range from typical Biharisporites through to specimens with variable development of curvaturae and thickness of intexine, through to typical Contagisporites. Records o f progymnosperms with in situ spores have been listed in Table VI. Within the Aneurophytales the in situ spores of Tetraxylopteris schmidtii and Rellimia thomsonii are well described, and b o t h included within the dispersed spore species Rhabdosporites langii. Lang (1926) recorded a spore attached to the side of a sporangium o f ReIlimia (Milleria) thomsonii, but this may be from another plant. Obhrel (1961) recorded spores from Protopteridium hostinense which are clearly comparable with Rhabdosporites langii. Lang (1925) recorded in situ spores from Protopteridium (Hostimella) pinnatum, which were poorly preserved and cannot be identified with certainty. Leclercq and Bonamo (1971) have n o w included both Protopteridium hostinense and Protopteridium (Hostimella) pinnatum within Rellimia thomsonii stating that they are all different stages of preservation of the same plant. An interesting point here is that Cathaiopteridium (Protopteridium) minutum is considered b y Obrhel {1966) and Leclercq and Bonamo (1971) to be very different from the genus Rellimia. However, I have seen the in situ spores recorded b y Halle (1936), and despite his description which suggests they are simple and laevigate, the spores can be placed in the dispersed spore genus Rhabdosporites. Bonamo (1975) does not include Cathaiopteridium within the progymnosperms, b u t the in situ spores suggest a comparison with the Aneurophytales. Aneurospora goensis, the in situ spore o f Aneurophyton germanicum, is more comparable with the spores o f the Archaeopteridale~ rather than other Aneurophytales, and bears a close resemblance to some specimens of Geminispora svalbardiae, the in situ spore of Svalbardia polymorpha, and to the microspores of the Archaeopteris species. Sections of Aneurospora goensis are needed in order to interpret the exact exinal stratification and equatorial features. Within the Archaeopteridales, the megaspores described from various species of Archaeopteris are all rather similar, and fall within the Biharisporites--Contagisporites complex. The microspores also appear to have a

264

TABLE VI In situ spores from the Progymnospermopsida Parent plant

Author

Spore construction and sculpture

Comparative dispersed spore(s)

Size (pro)

Age

Tetraxylopteris s c h m i d t i i

Bonarno and Banks (1967)

cavate, apiculatc with flat-topped elements

Rhabdosporites langii

73 - 1 7 6

L a t e Dev.

Ancurophyton germanicum

Streel (1964)

crassitate, apiculate

A n e u r o s p o r a goensis

39--60

Middle Dev.

Rellimia thornpsonii

Leclercq and Bonamo (1971 )

cavate, apiculate with flat-topped elements

Rhabdosporites langii

77--130

Middle Dev.

R. l h o m p sonii (Protopteridium hostinense)

Obrhel (1961)

cavate, apiculate w i t h a fine granulation

Rhabdosporites langii

: 100

Middle Dev.

R. thotnps~)nii (Hostirn ella pinnata)

Lang (1925)

indeterminate

indeterminate

:

Cathaiop tericliurn tProtopteridiumj minutum

Halle ( 1 9 3 6 )

cavate, apiculate with flat-topped elements

Archaeopteris latifolia

Arnold (1939) (see also Pettitt, 1965)

megaspores cavate, Biharisporites sp. variable o r n a m e n t microspores: exine Gerninospora sp. two-layers, aPieulate

Beck (1960)

?microspores: granulate

cf. G e m i n o s p o r a sp.

44--68

L a t e Dev.

Pettitt (1965)

megaspores: cavate, variable o r n a m e n t microspores: exine

Biharisporites sp.

110---370

L a t e Dev.

G e m i n o s p o r a sp.

45---75

Biharisporiles sp. Contagisporites sp.

170--469

G e m i n o s p o r a sP.

33-68

Biharisporites sP. Contagisporites sp.

).50--420

L a t e Dev.

1 7 0 - 413

L a t e Dev.

A . cf.

A. cf.

Middle

Dev.

macilen ta

jachsoni

100

R h a b d o s p o r i t e s sp.

Middle Dev.

300

L a t e Dev.

35--50

two-layers, apiculate A. halliana

Phillips et al. (1972)

megaspores: cavate, variable ornament, some evidence of culvaturae microspores: compared with

L a t e Dev.

A. latifolia A. rnacilenta

Phillips et al. (1972)

megaspores: cavate, variable ornament, some evidence of eurvaturae mierospores: s i m i l a r to

G e m i n o s p o r a sp.

A. halliana Archaeopteris sp.

Phillips et al. ( 1 9 7 2 )

megaspores: eavatc Contagisporites sp. vaxiable o r n a m e n t , curvaturate Geminospo rasp. microspores: exine t w o - l a y e r s , e v i d e n c e A n e u r o s p o r a sP. of a c r a s s i t u d e in s o m e

33--68

265

TABLE VI (continued) Parent plant

Author

Spore c o n s t r u c t i o n and sculpture

Comparative dispersed spore(s)

Size (/~m)

Age

A. fissilis

Andrews et al. (1965)

?microspores: granulate, n o o t h e r details given

indeterminate

60

Late Dev.

Svalbardia polymorpha

Hoeg (1942) Vigr an (1964)

exine two-layers, finely granulate, evidence of a crassitude in a few specimens

Geminospora svalbardiae

47--120

Middle Dev.

some m a y be

Aneurospora cf. greggsii

similar construction. Pettitt (1966, pl.3, fig.l) illustrates a section of A. cf.

jacksoni which shows the exine to be o f two layers. Phillips et al. (1972) also record a double layer in certain microspore specimens. They all have a similar ornament of small cones and granules, and there is evidence in some specimens (see Phillips et al., 1972, pl.45, fig.49) of a crassitude. Geminispora svalbardiae also has a two-layered exine (Allen, 1965) and as mentioned earlier shows the same variation from typical Geminospora type spores to those with some development of a crassitude, which could be included within the genus Aneurospora. The similarity between the microspores of Archaeopteris and the spores of Svalbardia polymorpha and Aneurophyton germanicum raise the possibility that the latter two species might be heterosporous; only the microspores having so far been recorded. INCERTAE SEDIS, WITH POSSIBLE PROGYMNOSPERM

AFFINITIES

Table VII shows those species with in situ spores which have some characters in c o m m o n with progymnosperms. The in situ spores of both Rhacophyton ceterangium and Oocampsa catheta differ markedly from those recorded for the progymnosperms, which have a close similarity. When more is known a b o u t the construction of in situ spores, this might be a useful pointer in separating these from the progymnosperms. The author does not agree with McGregor (1973, p.58) in including the genus Samarisporites within Grandispora. In his emended diagnosis of Grandispora he refers to the spores as being camerate (cavate). I would prefer to retain Samarisporites as a spore of similar ornament, but with a strong equatorial feature (zonate). It is essential for the spores of Oocampsa catheta to be sectioned before the exact construction is known, but it appears to be more like Samarisporites than Grandispora in construction. The present author (Allen, 1965) included Perotrilites eximius within t h a t genus on the basis o f its having a three-layered exine in which the outer layer was thinner than the layer immediately to the inside, even though the outer layer was moderately thick in relation to some species of Perotrilites. Those specimens of Oocampsa which compare with P. eximius need to be sectioned for comparison.

266 TABLE VII

In situ spores of plants here placed in Incertae Sedis, which have certain affinities with the Progymnospermopsida Parent plant

Author

Spore construction and s c u l p t u r e

Comparative dispersed spore(s)

Size Ozm)

Age

Rhacophyton ceterangium

A n d r e w s and Phillips (1968)

perinate, outer l a y e r sparsely apiculate

Perotrilites cf. P. c o n a t u s or P. p e r i n a t u s

401-70

L a t e Dev.

Oocampsa catheta

A n d r e w s et al. (1975)

zonate, possibly cavate~ o u t e r surface w i t h c o n e s a n d spines, o f t e n biform

cf. Perotrilites exirnius

96-120

Middle Dev.

Chaleuria cirrossa

A n d r e w s et al. (1974)

large s p o r e s : c u r v a tttrate, a z o n a t e , mostly apieulate small pores: azonate, curvatur a t e or c r a s s i t a t e or s o m e w i t h o u t either~ a p i c u l a t e

cf. S a m a r i s p o r i t e s praetervisus

A p i c u l i r e t i s i s p o r a sp. 6 0 - - 1 5 6 Cyelogranisporites cf. f l e x u o s u s A n e u r o s p o r a cf. 30---48 goensis cf. P r o c o r o n a s p o r a sp.

Eaxly or Middle Oev.

Some of the smaller spores of Chaleuria cirrosa can be included within the genus Aneurospora (Streelispora). Andrews et al. (1974) compare the ornam en t o f these with A. goensis the in situ spore of Aneurophyton germanicum. CONCLUDING REMARKS This review has recorded the spores f ound in situ in Late Silurian and Devonian plants. The comparisons with dispersed spores are oft en tentative, and are those o f the present author; but t hey are in most instances based on the descriptions and illustrations of the original authors. Many of these, particularly in the earlier records are poor, and the spores need restudying. Nearly all o f th em need sectioning to determine the exact construction. Certain similarities can be seen within some of the classes, especially in the T r i m e r o p h y t o p s i d a and Progymnospermopsida. The spores of the Khyniopsida and Zosterophyllopsida are rather similar. A large n u m b e r of interesting, c o m m o n and easily recognisable Devonian dispersed spore genera have yet to be found in situ. There are no records of the mu r o r n ate genera Dictyotriletes, Convolutispora or the prom i nent l y ribbed species o f Emphanisporites. No strongly patinate spores, as for example Archaeozonotriletes and Cymbosporites have been reported. There are no records of the abundant and d o m i n a n t l y Devonian genera Hystricosporites and Ancyrospora with their grapnel-tipped spines; though we do know that Nikitinsporites is from a lycopsid. Even if poorly preserved, these and m a n y o th er genera should be easily recognisable. It may be that many of the plants producing these spores were living in upland regions and only the easily transported spores are preserved. However, it is hoped that eventually

267

many of these dispersed spore types, will be linked with their parent plants, which will enable us to get a much better picture from dispersed spore assemblages of the macroplant flora; which in turn will give more information on plant evolution and distribution. REFERENCES

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