Nymphaeaceae

Review of Palaeobotany and Palynology, 33 (1981): 57--67 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

57

The Northwest European Pollen Flora, 25

NYMPHAEACEAE

MARILYN R. JONES and G.C.S. CLARKE

British Museum (Natural History), Cromwell Road, London SW7 5BD (Great Britain) LITERATURE Agababian (1973), Beug (1961), Erdtman (1943, 1952, 1969), Erdtman et al. (1961, 1963), Faegri and Iversen (1975), Kuprianova (1948), Meyer (1964), Moore and Webb (1978), Roland (1969), Walker (1974). INTRODUCTION AND TERMINOLOGY

The Nymphaeaceae is generally accepted to be one of the most primitive families of the angiosperms and this view is supported by pollen morphology. Pollen grains of this family in Northwest Europe are bilaterally symmetrical and have a single aperture. These are characters which are often associated with the pollen of gymnosperms or m o n o c o t y l e d o n s and are restricted to the most primitive dicotyledonous plants (Erdtman, 1952). Walker (1976a) has reported that the grains of many members of the Nymphaeaceae have no columellae b u t show instead a granular layer within the thickness of the exine. This feature, Walker argues, is another indication of the primitive phylogenetic position held by the family. Taken as a whole, the Nymphaeaceae is a eurypalynous family (Erdtman, 1969; Walker, 1976b) b u t the restricted range of species present in Northwest Europe (four species in t w o genera) limits the range of variation present in the pollen. Despite the small number of species, there is considerable inconsistency in the literature in the way the morphology of the pollen grains of this area is described. Most of the disagreements concern the apertures and a short explanation is necessary to justify the system followed in this paper. There are t w o matters which concern us here. The first is strictly a question of terminology. Because the apertures in Nymphaeaceae pollen are in the distal face of the grains (Plate IV, 3) and do n o t run from pole to pole, they should, according to Erdtman's (1952) system be referred to as sulci if elongate or ulci if rounded. Erdtman (1952) naturally used this system and he has been followed b y Walker (1976a, b). However, in order to determine whether an aperture is a sulcus rather than a colpus, it is necessary to know h o w the grain was positioned in its tetrad; it cannot be decided b y examination of the mature grain once it has lost contact with its sister grains. Thus, for a practical system which is intended for the identification of free pollen grains, the distinction between sulcus and colpus is irrelevant despite its great morphogenetic significance. Because of this, many works with predominantly practical 0034-6667/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company

58 a i m s s u c h as t h o s e o f Faegri a n d Iversen ( 1 9 7 5 ) or M o o r e a n d W e b b ( 1 9 7 8 ) l i m i t t h e m s e l v e s t o t h e c o l p u s / p o r u s t e r m i n o l o g y a n d we will f o l l o w t h e i r p r a c t i c e here. T h e o t h e r p r o b l e m is m o r e a m a t t e r o f i n t e r p r e t a t i o n a n d c o n c e r n s the d e s c r i p t i o n o f t h e a p e r t u r e s o f N y r n p h a e a pollen. In N o r t h w e s t E u r o p e t h e species o f this genus h a v e an a p e r t u r e w h i c h c o u l d be i n t e r p r e t e d as a single, n a r r o w c o l p u s t h a t encircles t h e grain a n d is sited t o o n e side o f t h e e q u a t o r . E r d t m a n ( 1 9 5 2 ) a n d Walker ( 1 9 7 6 b ) t a k e this view a n d t h u s r e f e r to t h e a p e r t u r e s o f N y m p h a e a as z o n i s u l c u l a t e . C h a n d a e t al. ( 1 9 7 9 ) also s t a t e t h a t the a p e r t u r e s are ring-like a n d r u n parallel to the e q u a t o r . We p r e f e r , h o w e v e r , t o f o l l o w B e u g ( 1 9 6 1 ) , Faegri a n d Iversen ( 1 9 7 5 ) a n d M o o r e a n d W e b b ( 1 9 7 8 ) in t a k i n g t h e o t h e r view, n a m e l y t h a t the a p e r t u r e is a v e r y large p o r e c e n t r e d on o n e p o l e a n d c o v e r e d a l m o s t c o m p l e t e l y b y an o p e r c u l u m . If this v i e w is t a k e n , it f o l l o w s t h a t t h e s e grains s h o u l d be r e f e r r e d to as m o n o p o r a t e . I t s e e m s t o us t h a t t h e l a t t e r v i e w is p r e f e r a b l e , firstly b e c a u s e t h e o r n a m e n t a t i o n o n t h e o p e r c u l u m is n o t t h e s a m e as t h a t on t h e rest o f t h e sexine, a n d s e c o n d l y b e c a u s e m o n o p o r a t e grains w i t h an o p e r c u l u m s e e m t o h a v e a closer m o r p h o l o g i c a l r e l a t i o n s h i p w i t h o t h e r p o l l e n t y p e s in t h e f a m i l y such as t h e m o n o c o l p a t e , o p e r c u l a t e grains o f N u p h a r or, i n d e e d , o f s o m e n o n - E u r o p e a n species o f N y m p h a e a . This r e l a t i o n s h i p is discussed in detail b y Walker ( 1 9 7 4 ) . G o d w i n ( 1 9 7 5 ) r e c o r d s t h a t p o l l e n grains o f N u p h a r a n d o f N y r n p h a e a have f r e q u e n t l y b e e n f o u n d in d e p o s i t s o f Q u a t e r n a r y age. T h e p o l l e n o f Brasenia p u r p u r e a , a species o f the closely r e l a t e d C a b o m b a c e a e w h i c h has o f t e n b e e n i n c l u d e d in the N y m p h a e a c e a e , has b e e n d e a l t w i t h in a s e p a r a t e a c c o u n t . SPECIMENS EXAMINED All the specimens listed here are housed in the herbarium of the British Museum (Natural History). Nuphar lutea (L.) Sibthorp and Smith -- Denmark : Dahl D6 ; England: Bangerter and Groves 275, Sims 1, Ward 50; Germany: Harz 5407 ; Sweden: Johansson s.n., Ringselle 803. N. lutea × N. p u m i l a - England: Young 538; Norway: Trethewy s.n.; Sweden: Svenonius 804; U.S.S.R.: Raenitz s.n. N. pumila (Timm) De Can dolle -- Denmark: Dahl D47; France: Vendrely s.n.; Norway: Holmboe s.n.; Scotland: Taylor s.n.; Sweden: Olsson et al. s.n. Nymphaea alba L. -- England: Bailey 36, Butler and Hall 503, Gerrans s.n., Paton s.n.; France: Gave 560, Murray s.n., Shuttleworth s.n.; Ireland: Wilmott 2332, Wilmott 2384; Scotland: Hanbury s.n., Wilmott 470713E; Sweden: Ek s.n., Johansson s.n., Smith s.n., Wahlstedt s.n.; U.S.S.R. (Estonia): Gruner s.n. N. candicla C. Presl -- Germany: Lechmann 4704; Sweden: Ahlberg s.n., Johansson s.n., Lohammar s.n., ()hrstedt s.n. KEY TO THE POLLEN TYPES 1.a. O r n a m e n t a t i o n b. O r n a m e n t a t i o n

lutea t y p e echinate (elements conical)...Nuphar b a c u l a t e , g e m m a t e or v e r r u c a t e ( e l e m e n t s n o t conical) • . . N y r n p h a e a alba t y p e

59 DESCRIPTIONS OF THE POLLEN TYPES

Nuphar lutea type (Plates I, II) Pollen class: 1-Colpate (sulcate). Heteropolar. Aperture: Colpus, long, fairly broad, usually deeply sunken; ends broadly obtuse, margin o f t e r centrally constricted, unthickened; large operculum present (may be lost during acetolysis), membrane restricted to a narrow strip round the operculum. Exine: Rather thin, slightly thinner in the area of the colpus than elsewhere. Stratification obscure in LM, nexine and sexine (excluding ornamentation) of a b o u t equal thickness in SEM sections. Columellae absent. Echinae in cross-section with acute or narrowly obtuse apices, uninterruptedly conical or with one or two constrictions, extending down through the sexine into the nexine sometimes producing verrucae on the inner face of the nexine. Inner face of the nexine otherwise smooth. Ornamentation : Echinate. Echinae long, stout, n o t arranged in patterns. Sexine surface between echinae psilate or finely scabrate in LM, SEM shows a complex weft of sporopollenin elements. Operculum and surrounding area bearing slightly smaller echinae than rest of grain. Outlines: Equatorial view 1 (colpus in side view) -- elliptic, the face with the colpus rather flattened; equatorial view 2 (colpus in end view) -reniform, colpus forming a deep invagination. Polar view (colpus in face view) -- elliptic, often narrowly so. Measurements: Glycerine jelly - - e q u a t o r i a l view (colpus seen from the side) : P 30--45 um, E 38--53 um, P/E ratio 0.77--0.90; polar view (colpus in face view): long axis (45)50--57(64) um, short axis (30)34--42(49) um; exine thickness 0.5--2.0 t~m; colpus 30--41 X 4--25 t~m; echinae 2--12 t~m tall, 1--3 pm wide at the base. Silicone oil -- equatorial view: P 27--41 t~m, E 34--47 gm, P/E ratio 0.75--0.90; polar view: long axis 40--58 pm, short axis 27--44 ~m.

Species: Nuphar lutea, N. lutea X pumila, N. pumila Comments As with Nymphaea, Moore and Webb (1978) include Nuphar species in their key to inaperturate pollen because the aperture might be overlooked. Almost all the grains of Nuphar examined during the preparation of this account, whether m o u n t e d in silicone oil or glycerine jelly, had collapsed so that the colpus was deeply invaginated. This means that the details of the aperture and its operculum are often difficult to see, b u t nevertheless, the existence of the aperture is not normally hard to verify. Another feature shared with Nymphaea is the difference in ornamentation on the operculum from that on the rest of the sexine. In the case of Nuphar the difference is n o t great but, as Wodehouse (1935) noticed in N. advena, the Northwest European species have echinae which are slightly smaller and more closely spaced on the operculum than elsewhere.

60 Both Erdtman (1943) and Godwin (1975) suggest that the pollen of Nuphar lutea can be distinguished from t h a t of N. pumila by its taller, more closely spaced echinae. We have tried to confirm this but have f o u n d that there is such an overlap of the range of variation between the two species t h a t to distinguish any but the more extreme variants is impracticable. We have, therefore, n o t been able to provide a reliable key to separate the pollen of these two species. Faegri and Iversen (1975) describe the echinae of Nuphar species as more than 5 pm long; it would be more accurate to say that the largest echinae are more than 5 pm long, since a substantial proportion are less than this as the following table shows: Species

Height of echinae (pm)

Nuphar lutea N. pumila N. lutea x pumila

3--12 2--8 2--9

Nymphaea alba type (Plates III, IV) Pollen class: 1-Porate. Heteropolar. Aperture : Porus, very large, occupying a little less than half the surface of the grain, slightly or deeply sunken; almost entirely covered by an operculum; membrane restricted to a narrow, indistinct ring encircling the grain near the equator, scabrate; costae and margo absent. Exine: Rather thin, often varying in thickness t h r o u g h o u t the grain. Stratification n o t apparent in LM; sexine as thick as, or thinner than nexine in SEM sections. Columellae absent. Sexine elements large, of variable shape. Inner face of nexine often covered by irregularly shaped verrucae; with minute puncta (SEM). Ornamentation: Gemmate and verrucate, often interspersed with blunt, cylindrical bacula (bacula sometimes absent), processes variable in shape, size and density. Sexine surface between processes psilate or scabrate. Operculum covered with lower processes than rest of grain, irregularly verrucate or scabrate. Outlines: Equatorial view (pore seen from the side) rounded, t h e p o r e (operculum) surface flattened or sunken in the centre, the remainder of the aperture forming shallow grooves at each side. Polar view (pore in face view) elliptic or circular. Measurements: Glycerine jelly -- equatorial view (pore seen from the side): P 22--31 pm, E 32--49 t~m, P/E ratio 0.59--0.81; polar view (pore in face view); long axis (26)30--47(51) gm, short axis (24)28--42(45) pm; exine thickness 0.5--3.0 p m; pore diameter 19--34 p m; gemmae up to 3.5 tl m tall; bacula up to 10(17) tim tall. Silicone oil -- equatorial view (pore seen from the side): P 21--29 #m, E 29~44 t~m, P/E ratio 0.57--0.79; polar view: long axis 25--48 pm, short axis 23--40 gm. Species: Nymphaea alba, N. candida.

61 Key to the species 1.a. Longest axis (26)30--38(42) pm; sexine processes scattered (see plate III, lb), bacula usually present . . . . . . . . . . . . . . . . . . . Nymphaea alba b. Longest axis (38)41--47(51) pm; sexine processes more dense (see plate III, 6b), bacula usually absent . . . . . . . . . . . . . . . . . . . N. candida Comments Although the pore in Nymphaea species is so large a feature of the pollen grain, it is not always easy to see and for this reason both Beug (1961) and Moore and Webb (1978) include the genus twice in their keys, once in the monoporate class and once in the inaperturate class. The difficulty is brought about by the huge operculum which can obscure the pore almost completely on occasions. It should, however, be possible to see the limits of the aperture with careful observation since the ornamentation on the operculum is different from that on the rest of the sexine. Occasionally, the pollen grains from species of this type remain associated in tetrads. It is possible that this m a y only be the case while the pollen is somewhat immature, but whatever the cause, these tetrads give a convenient means of demonstrating t h a t the pore in Nymphaea species is sited at the distal pole of the grain. This can be seen clearly in Plate IV, 3. The ornamentation of Nymphaea pollen grains is very variable. It is composed of a range of differently shaped processes -- verrucae, gemmae and bacula -- which vary considerably in height, density and relative frequency. This variation occurs n o t only in the grains of different specimens of a species but also in different grains within a specimen. It has been suggested (e.g. by Clapham et al., 1962) that a subspecies of N. alba, N. alba subsp, occidentalis Ostenfeld, can be distinguished by its small size and by its uniformly short exine projections on the pollen grains. We have examined a number of specimens named subsp, occidentalis and could find no correlation of this kind: the specimens labelled subsp, occidentalis fell within the same range of variation as those named subsp, alba. It is also reported in the taxonomic literature that N. alba can be distinguished from N. candida by the size of its pollen grains. Tutin (1964), for example, describes the pollen of N. alba as "c. 20 t~m in diameter, pale yellow, rugose and papillate with rod-shaped papillae" and t h a t of N. candida as "c. 35 t~m in diameter, deep yellow". Since it is not possible to use colour as a character in acetolysed grains, the only distinguishing character here is the size of the grains. Presumably Tutin's measurements were given for untreated grains and we have f o u n d t h a t acetolysed grains are considerably larger. We also f o u n d t h a t the distinction in size is not nearly so clear-cut as Tutin's figures suggest. The average size of N. candida grains is greater than the average size of N. alba grains, but the ranges of the two species overlap. There is usually, however, a difference in ornamentation since the sexine processes in N. candida are normally more densely spaced than those in N. alba, and N. candida rarely carries bacula. Using size and ornamentation in conjunction, one can be reasonably confident in separating the pollen grains of these two species.

62

Plate descriptions PLATE I (×1500; p. 63)

Nuphar lutea (L.) Sibthorp and Smith (figs.l, 3, 4 Harz 5407; fig. 2 Johansson s.n.) 1. Polar view; cross-section. 2. Ornamentation; bases of echinae and scabrate rectum. 3. Equatorial view (colpus in end view); cross-section. 4. Polar view; close up of colpus PLATE II (1, 3 x 1500; 2 x 5000; p. 64)

Nuphar lutea (L.) Sibthorp and Smith (Harz 5407) 1. Scanning electron micrograph ; equatorial end view. Nuphar lutea x pumila (Raenitz s.n.) 2. Scanning electron micrograph; ornamentation between echinae. Nuphar lutea (Harz 5407) 3. Scanning electron micrograph; polar view of colpus with operculum. PLATE III (X1500; p. 65)

Nymphaea alba L. (Paton s.n.) 1. a. Polar view; cross-section, b. Ornamentation on face opposite aperture. 2. Partially detached operculum. Nymphaea candida C. Presl (Ohrstedt s.n.) 3. Equatorial view; cross-section, operculum at top. Nymphaea alba L. (Paton s.n.) 4. Partially detached operculum. 5. Ornamentation on operculum at high focus. Nymphaea candida C. Presl (Ohrstedt s.n.) 6. a. Polar view showing operculum, b. Ornamentation on face opposite aperture. PLATE IV (figs.l--3, 5, 6 x 1500; 4 x 10,000; p. 66)

Nymphaea alba L. (figs.l, 2, 4, 5 Johansson s.n.; fig.3 Butler and Hall 503) 1. Scanning electron micrograph; face opposite aperture. 2. Scanning electron micrograph; equatorial view, operculum at top. 3. Scanning electron micrograph ; tetrad showing polarity of grains. 4. Scanning electron micrograph; fractured exine. 5. Scanning electron micrograph; fractured grain. Nymphaea candida C. Presl (C)hrstedt s.n.) 6. Scanning electron micrograph; polar view showing ornamentation on operculum.

63 PLATE I (Nuphar lutea type)

2

v

64

PLATE II (Nuphar lutea type)

65 PLATE III (Nymphaea alba type)

~qL4

67 REFERENCES Agababian, V.S., 1973. Pollen of Primitive Angiosperms. Izdatel'stvo Akad. Nauk Armyanskoi S.S.SR., Erevan, 169 pp. (in Russian). Beug, H.-J., 1961. Leitfaden der Pollenbestimmung, 1. Lieferung. G. Fischer, Stuttgart, 63 pp. Chanda, S., Ghosh, K. and Nilsson, S., 1979. On the polarity and tetrad arrangements in some mono- and diaperturate angiosperm pollen grains. Grana, 18: 21--31. Clapham, A.R., Tutin, T.G. and Warburg, E.F., 1962. Flora of the British Isles. Cambridge University Press, Cambridge, 2nd ed., 1269 pp. Erdtman, G., 1943. An Introduction to Pollen Analysis. Chronica Botanica Co., Waltham, Mass., 239 pp. Erdtman, G., 1952. Pollen Morphology and Plant Taxonomy. An Introduction to Palynology, I. Angiosperms. Almqvist and Wiksell, Stockholm, 539 pp. Erdtman, G., 1969. Handbook of Palynoiogy. Munksgaard, Copenhagen, 486 pp. Erdtman, G., Berglund, B. and Praglowski, J.R., 1961. An introduction to a Scandinavian pollen flora. Grana Palynol. 2(3): 3--92. Erdtman, G., Praglowski, J.R. and Nilsson, S., 1963. An Introduction to a Scandinavian Pollen Flora, II. Almqvist and Wiksell, Uppsala, 89 pp. Faegri, K. and Iversen, J., 1975. Textbook of Pollen Analysis. Munksgaard, Copenhagen, 3rd ed., 295 pp. Godwin, H., 1975. The History of the British Flora. A Factual Basis for Phytogeography. Cambridge University Press, Cambridge, 2nd ed., 541 pp. Kuprianova, L.A., 1948. Pollen morphology of monocotyledons. Tr. Bot. Inst. Akad. Nauk S.S.S.R., Ser. 1, 7:163--262 (in Russian). Meyer, N.R., 1964. Palynological studies in Nymphaeaceae. Bot. Zh. S.S.S.R. 49: 1421--1429 (in Russian). Moore, P.D. and Webb, J.A., 1978. An Illustrated Guide to Pollen Analysis. Hodder and Stoughton, London, 133 pp. Roland, F., 1969. Etude ultrastructurale des apertures, III. Pollen Spores 11: 475--498. Tutin, T.G., 1964. Nymphaeaceae. In: T.G. Tutin, V.H. Heywood, N.A. Burges, D.M. Moore, D.H. Valentine, S.M. Waiters and D.A. Webb (Editors), Flora Europaea, 1. Cambridge University Press, Cambridge, pp.204--205. Walker, J.W., 1974. Aperture evolution in the pollen of primitive angiosperms. Am. J. Bot., 61: 1112--1137. Walker, J.W., 1976a. Evolutionary significance of the exine in the pollen of primitive angiosperms. In: I.K. Ferguson and J. Muller (Editors), The Evolutionary Significance of the Exine. Academic Press, London, pp.251--308. Walker, J.W., 1976b. Comparative morphology and phylogeny of the Ranalean complex. In: C.B. Beck (Editor), Origin and Early Evolution of Angiosperms. Columbia University Press, New York, N.Y., pp.241--299. Wodehouse, R.P., 1935. Pollen Grains. McGraw-Hill, London, 574 pp.