Origin and evolution of lycopods

C. G. K. Ramanujam

Ramanujam CGK 1992. Origin and evolution of lycopods. Palaeobotanist 41 51·57.

The lycopods are known from as early as Sieginean Stage of the Lower Devonian. Lower and Middle Devonian lycopods were all herbaceous. Arborescent taxa appeared by Upper Devonian (e.g., Cyclostigma and Lepidosigillaria). The microphyllous foliage of lycopods seem to have originated from enations as well as telomic trusses. The lycopods auained peak of their evolution during the Upper Carboniferous. Towards the close of the Carboniferous and dawn of the Permian, with gradual dWindling and disappearance of swamps, the lepidodendrids suffered drastic decline numerically and phytogeographically. General aridity of the Triassic resulted in acute dwarfing as evidenced by Pleuromeia. This trend continued funher resulting in the highly telescoped Nathorstiana during the Cretaceous. The earlier lycopods were homosporous; heterospory appeared by Upper Devonian. Heterospory ran rampant in the Lepidodendrales. The ultimate in heterospory and the approach to seed habit could be witnessed in Lepidocarporz. Four discrete types of strobilus organization could be recognized by the Lower Carboniferous, viz., 1. Lepidostrobus type, 2. Mazocarpon type, 3. Achlamydocarpon type, and 4. Lepidocarpon type. Recent studies point towards the origin of lycopods along rwo different pathways, with both Zosterophyllopsida and Rhyniopsida representing the progenirors All available evidence show that Lycopsida constitutes a "Blind Alley" in the evolution of vascular plants. Key-words-Lycopsida, Origin, Geological hisrory, Evolution.

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UNEQUIVOCAL members of Lycopsida could be environment. The Permian Period, which witnessed recognized from as early as Sieginean Stage of the rapid dwindling and disappearance of swamps, Lower Devonian coexisting with the zosterophyllop· heralded their decline. The overall arid Triassic sids and rhyniopsids. They soon underwent rapid Period triggered drastic physical, numerical and multiplication and radiation qualitatively and phytogeographic diminution of the lycopods. The quantitatively all through the Devonian, and by geological history of the Lycopsida closely parallels Carboniferous Period attained developmental that of the Sphenopsida which, however, suffered climax, both vegetatively and reproductively, as exemplified by numerous herbaceous and Essays In Evolutionary Plant Biology arborescent taxa that dominated the swampy Editors, B. S. Venkatacha12, David L Dllcher & Harl K. Maheshwarl Publisher' , Blrbal S.hnl Institute of PaJ.eobolany, Lucknow 52 THE PALAEOBOTANIST much more drastic decline. Thomas (1978), Phillips Lepidodendrales - Upper Devonian to (1979) and DiMichele and Phillips (1985) have Permian provided superb overviews of the morphology, Pleuromeiales - Triassic to Cretaceous reproductive biology and ecological adaptation of Lycopodiales - Upper Carboniferous the Palaeozoic arborescent lycopods. to Recent The extant Lycopsida comprises five genera, Selaginellales - Upper Carboniferous viz., Phylloglossum, Lycopodium (Lycopodiaceae), to Recent Selaginella (Selaginellaceae) and Isoetes and Stylites lsoetales - Triassic to Recent (Isoetaceae). If Stylites is considered as a subgenus of Isoetes (see Kramer & Green, 1991), only four VEGETATIVE CHARACTERS genera constitute the extant lycopods. In the geological past, however, the lycopods enjoyed The Lower and Middle Devonian lycopods were better representation at the genus, family and order all herbaceous (e.g.) Baragwanathia, levels. Drepanophycus, Protolepidodendron, Colpodexylon, etc.). Shrubby or moderately arborescent habit GENERAL CHARACTERS AND appeared by the Upper Devonian as evidenced by CLASSIFICATION Lepidosigillaria and Cyclostigma which often attained a height of 8 m and a girth of 30 em. During The lycopods are a well·knit, homogeneous the Carboniferous the arborescent lycopods had group of lower vascular plants. The essential features their best expression in forest giants such as of lycopods are: plants usually herbaceous but Lepidodendron, LepidophloiOs, Sigillaria and occasionally arborescent with dichotomous or a Bothrodendron. It is generally suggested that the combination of dichotomous and monopodial Upper Devonian taxa, such as, Lepidosigillaria and branching; leaves helically disposed microphylls Cyclostigma constitute the transitional forms and the with a prominent unbranched midvein that does not possible precursors of the Carboniferous leave any leaf gap in the stele of stem; vasculature of arborescent lycopods. Banks (1960) opined that stems protostelic or siphonostelic with protoxylem there was a group of diverse herbaceous Devonian in exarch position; arborescent taxa with limited lycopods with eligulate foliage, lack of leaf cushions secondary xylem; a single sporangium borne in the and homospory which subsequently gave rise to axil or on adaxial surface of sporophyll; sporophylls arborescent forms along one line and newer generally aggregated to form discrete strobili; plants herbaceous forms along the other. Andrews (1961) homosporous or heterosporous. visuali zed a common stock from which all the Drepanophycales, Protolepidodendrales, arborescent taxa developed. The lycopods of the Lycopodiales, Selaginellales, Lepidodendrales, Carboniferous and Permian furnished' greatest Pleuromeiales and lsoetales are usually recognized diversity of form incorporating small, insignificant in various systems of classification proposed since herbaceous taxa referable to Lycopodiaceae and 1960 (Delevoryas, 1962; Sporne, 1966; Bierhorst, Selaginellaceae (e.g., Lycopodites, Selaginellites, 1971; Stewart, 1983; Taylor, 1983; Meyen, 1987). Paurodendron, etc.), moderately arborescent (some Bierhorst (1971) included Asteroxylales also under species of Lepidodendron, Paralycopodites), and lycopods, and Meyen's (1987) lsoetales huge, majestic arborescent Lepid0dendrales often encompasses the Lepidodendrales and attaining a height of 50 m and occupying extensive Pleuromeiales of others. The author, however, tracts of swamps (Lepidodendron, LepidophlOiOS, agrees with Stewart (1983) that Asteroxylon Sigillaria, etc.) in the Euramerica. notwithstanding its similarities with lycopods, The branching of the axes was almost deserves inclusion only under Zosterophyllopsida. exclUSively dichotomous in the earliest forms and a Further, the traditional treatment of lsoetales is combination of dichotomous and monopodia I followed in this contribution. Lycopodiales, nature in the later forms. The foliage of lycopods Selaginellales and lsoetales consist of both extinct should be technically designated as microphylls and extant members; the remaining taxa are irrespective of their size as they possess a single represented by only extinct members. The following unbranched midvein not associated with any leaf are the geological ranges of the various lycopod gap in the central vascular cylinder of the stem. The orders: leaves disposed in a lax or close-knit helix or Drepanophycales Devonian pseudowhorls may be scale-like, linear, deltoid and Protolepidodendrales Devonian to Lower more or less laminar (Fairon-Demaret & Banks, Carboniferous 1978). They may be entire or as in some Devonian RAMANUJAM-ORIGIN AND EVOLUTION OF LYCOPODS 53 taxa forked (Protolepidodendron), trifurcate primeval condition in some lycopods. It now (Colpodexylon) or split up into five lobes appears probable that the microphylls of lycopods (Leclereqia). Further. the leaves may be perennial or could have evolved along two divergent pathways, show abscission leaving prominent leaf cushiuns of one involving enations and the other, telomic varied shapes (e.g .. Lepidodendrales), trusses. Concomitantly, the microphylls- of all the The stelar anatomy of the lycopod stems shows lycopods need not necessarily be considered as well-defined trends of evolution from various types homologous structures. of protostele to mixed protostele and ultimately the With the dWindling and large scale siphonostele. The protosteles of the Devonian disappearance of swampy habitats by the end of the lycopods may be lobed. as in, Drepanopbyclls, Upper Carboniferous and the dawn of the Permian, Colpodexylon and Archaeosigillaria, or with many of the arborescent lycopods such as numerous small marginal, teeth-like ridges, as in, Lepidodendron and Lepidopbloios suffered drastic Protolepidodendron and Leclereqia. The lobed decline but Sigillaria, and smaller lepidodendrids protostele resembles the steles in some of. the such as Paralycopodites survived along with a modern species of Lycopodium; the ridged type is number of herbaceous forms. The Triassic witnessed comparable with the primary xylem of some of the acute diminution in the arborescent habit resulting arborescent lepidodendrids (e .g., LepidophloiOs). in much smaller forms like Pleuromeia which The lepidodendrids show solid protQsteles attained a maximum height of 2 m. Both the aerial (Lepidodendron scleroticum), mixed protosteles and subterranean systems of the lepidodendrids (Lepidodendron uasculare) and siphonosteles such as Sigillaria underwent extreme reduction as (Lepidodendron hickii, Sigillaria approximata). The exemplified by Pleuromeia. Further reduction in the arborescent forms possess cambial activity resulting aerial system could have led to Nathorstiana 00-15 in secondary tissues. The vascular cambium is, em) of the Cretaceous. Earlier it was felt that lsoetes however, unifacial forming only secondary xylem probably represents the end product of this and no secondary phloem (Eggert & Kanemoro, continued trend of reduction starting from Sigillaria 1977 ). (Magdefrau, 1956). Based on his study of The microphylls of lycopods are generally Protostigma ria, Jennings (1975) argued that the considered to have been evolved from enations lobed rhizophore of !soetes might not have evolved (Bower, 1935; Banks, 1968; Gensel, 1975). from the dichotomous stigmarian root system of According to this concept, the microphylls arborescent lycopods. Pigg and Rothwell (1979) originated from non-vascularized spine-like enations recently suggested that lsoetes and Stylites may have seen in some zosterophyllopsid taxa, viz., Sawdonia, had their origin in Lepidodendron plants of smaller Kaulangiophyton, etc. The enations of Asteroxylon, stature possessing basal cormose rhizophore, where in a vascular trace emanating from the axial instead of a regular stigmarian type of branched protostele stops short abruptly at the base of the rooting system. The bisporangiate strobili, and ti~Q enation rather than entering it, represent obviously similarity between the megagametophytic structures the intermediate step in the evolution of of !soetes and Lepidodendraceae furnish additional microphylls. The extension of the vascular trace into support to this line of thinking (Brack-Hanes, 1978). the enation results in a microphyll with a single The Upper Devonian moderately arborescent midvein as exemplified by Drepanopbycus and lycopods like Lepidosigillaria and Cyclostigma with Baragwanathia, two of the earliest lycopods. A basal once- or twice-lobed corm-like rhizophores continued elaboration of the simple microphyll could be the progenitors of the line that resulted in could result in the variously lobed microphylls of Isoetes-like plants. The recent discovery of lsoetiles the protolepidodendralean taxa. from the Triassic (Brown, 1958; Bock, 1962) lends The telomic origin of microphylls originally support to this view. Pleuromeia and Nathorstiana proposed by Zimmermann (1952) did not receive thus appear to have evolved (or devolve<;l!) along a much support for a long time. The recent studies of different pathway than that of !soetes and Stylites. Schweitzer (1980) and Bonamo and Grierson (1981) which highlight the 3-dimensional nature of the REPRODUCTIVE CHARACTERS fertile and sterile microphylls of Protolepidodendron and Leclereqia have provided fairly convincing One of the diagnostic features of Lycopsida is evidence for the origin of some microphylls by the presence of a single, globose, reniform or overtopping and reduction of telomic trusses (see elongated sporangium either in the axil or on the also Stewart, 1983). In accordance with thiS concept, adaxial facet of the sporophyll. Many of the Lower the variously lobed microphylls would represent and Middle Devonian lycopods, viz., 54 THE PAlAEOBOTANIST

Baragwanathia, Drepanophycus, Protolepidoden· (= Flemingites), Bothrodendrostrobus, Sporangio­ dron, Cyclodendron, Leclereqia, etc. do not show any strobus, etc., and closely resembling the extant perceptible difference berween the sporophylls and Selaginella, (i i) Ma zoca rpon ·type shOWing vegetative leaves. The sporophylls in these taxa may intrasporangial modification in the form of a be seen interspersed among the leaves or loosely parenchymatous pad or cushion, (iii) grouped into discrete fertile zones alternating with Achlamydocarpon'rype with megasporangial and the leaves, simulating the situation seen in the sporophyll modification (the megasporangial wall modern Lycopodium selago. In other words, no being multilayered and sclerotiC and the sporophyll organized strobili were known in the Lower and pedicel prominently keeled), and (iv) lepidocarpon­ Middle Devonian lycopods. Well·organized strobili type which is integumentary (Phillips, 1979). The were encountered only from the Upper Devonian latter three rypes are monosporangiate; of these onwards. The absence of organized strobili may then Achlamydocarpon and Lepidocarpon are be considered as a primeval condition in lycopods. monosporic. The Lower and Middle Devonian lycopods were Unlike Lepidostrobus, in Mazocarpon the all homosporous. By the Upper Devonian time megasporangium-sporophyll complexes are shed heterospory appeared as evidenced by the from the cone and disseminated by wind and water. bisporangiate strobili of Cyclostigma (Chaloner, The megasporangium·sporophyll units of 1968). Phillips (1979) has prOVided a masterly Achlamydoca1pon and Lepidocarpon simulate boat­ analysis of the strobil us organization and like structures and functioned as propagules reproductive biology of the arborescent lycopods. (dissiminules) well adapted to dispersal by water. In addition to the Devonian herbaceous The fertili zation and embryo development in these Drepanophycales and Protolepidodendrales, the took place most probably after their separation from modern Lycopodiales are homosporous. the parent plants and. release into the swamp Lepidodendrales, Pleuromeiales, Selaginellales and (Phillips, 1979; DiMichele & Phillips, 1985). The Isoetales are, however, strictly heterosporous. The free sporing bisporangiate Lepidostrobus rype with heterosporous taxa are invariably Iigulate but the many small megaspores per sporangium, homosporous ones, are as a rule, eligulate encountered more frequently than other types norwithstanding the recent discovery of ligulate, during the Lower Carboniferous, may be considered homosporus Leclereqia (Banks, Bonamo & Grierson, as least specialized structurally in its adaptation to 1972). swampy environment. A gradual reduction in the number of The nature of sporangial protection in megaspores per mega sporangium and the arborescent lycopods also furnishes distinct trends concomitant increase in the size of the remaining of evolution. The sporangium in Lepidostrobus, megaspores seems to be most potent trend of where the pedicel of sporophyll is simply T-shaped evolution within the heterospory. The highly in cross section, is least protected and represents the advanced heterospory is the one in which a large primitive condition. The Lepidocarpon sporangium functional megaspore is retained within the ensheathed by well·developed lateral lamina megasporangium as exemplified by Miadesmia, ("integument') is best protected and evolutionarily, Achlamydocarpon, Lepidoca1pon and some species more advanced. Lepidostrobopsis and Lepidocar· of Selaginella (5. monospora, S. su!cata). The popsis of Abbott (1963) are intermediate berween ultimate in the heterospory coupled with the the above rwo extremes. In Achlamydocarpon, a approach to seed habit had itS expression in multilayered sclerotic wall affords protection to the Lepidocarpon lomaxi (strobilus referable to sporangium (Schumaker·Lambry, 1966). Balbach Lepidophloios) which for all intents and purposes (1962) and Ramanujam and Stewart (1969) have functioned as a seed. The studies of Ramanujam and provided detailed information on the developmental Stewart (1969) and Phillips (1979) have clearly stages of the lateral lamina in Lepidocarpon. shown that Lepidocarpon is an integumented Lepidostrobus, Lepidostrobopsis, Lepidocarpopsis and dehiscent megasporangium with a Single functional Lepidocarpon show the follOWing trends of megaspore. evol uti on in the sporangial protection by its By the Early Carboniferous (MisSissippian) four progressive ensheathment, viz. (i) lateral extension distinct types of strobilus architecture, primarily or alation of the pedicel on either side of its vein based upon megasporangium-megasporophyll portion, (i i) grad ua I upturning of the alation to units, could be recognized in the arborescent enfold the sides of the basal half of sporangium, and lycopods, viz. (i) free sporing bisporangiate (iii) further elaboration and upward growth of the Lepidostrobus·rype exemplified by Lepidostrobus alation to form well·developed lateral lamina that RAMANUjAM-ORIGIN AND EVOLUTION OF LYCOPODS 55

A B c o E

Text-figure 1- Diagrammalic cross sections of sporophylls of: A. Lepidoslrobus, B. Lepidoslrobopsis, C. Lepidocarpopsis lanceolalus, D. L. semialala, and E. Lepidocarpon showing progressive enshealhmenl of the sporangia (redrawn from Ramanujam & Stewart, 1969). completely ensheaths the sporangium leaving a plants (Banks, 1967, 1968; Banks & Davis, 1969) narrow slit (Text-figure 1). Lepidocatpon may then have brought ro light convincing evidence for be considered as a highly advanced reproductive treating Zosterophyllopsida as the progenirors of organization of arborescent lycopods that closely lycopods. Banks (1968) proposed that lycopods are mimicked the seed habit, which incidentally was monophyletic and had their origin from also evolVing during the Carboniferous. In zosterophylls, with Asteroxylon. or taxa of similar Lepidocatpon, however, the integument·like lateral nature, as transitional forms. In the possession of laminae were outgrowths of the sporophyll pedicel, massive elliptiC or terete prorosteles with exarch while the integuments of seed plants had their protm,:ylem and globose ro reniform stalked lateral origin from the reduction and concrescence of a sporangia with distal dehiscence in addition ro branching system. dichoromous or pseudomonopodial branching with spirally disposed spine·like enations. the ORIGIN OF LYCOPODS zosterophylls are, no doubt, genetically related ro lycopods Recent thought provoking studies on the Stewart (1983), \"ho included Asteroxylales amiquiry, origin and evolution of early vascular under Zosterophyllopsida, has argued that lycopods

PLEUROMEIALES ISOETALES 1 / (Reduc~i

LYCOPOOIALES I LEPIDODENORALES SELAGINELLALES / r ( A, ~"nt~- H"" o,po<'"' )(H"b" ""' - H" ,,"p"'", ) OREPHANfPHYCALES /

PROTOLEPIDODENDRA LES

IZOSTEROPHYLLOPSIOAL_ ••••••••••••• /

IRHYNIOPSIDAj

Text-figure 2- Phylogenetic concepls of Lycopsida based upon recent sludies. 56 THE PALAEOBOTANIST

had two different sources of ongIn, viz., Banks HP 1967. The stratigraphic occurrence of early land plants Zosterophyllopsida and Rhyniopsida. He considers and its bearing on their origin. In Oswald DH (Editor)­ International Symposium Devonian Systematics 2: 721·730. Zosterophyllopsida as ancestral to Drepanophycales Alberta Soc. Petrol. Geol. Calgary, Canada. which subsequently gave rise to the eligulate, Banks HP 1968 The early history of land plants. In Drake homosporous Lycopodiales. The second source in ET (Editor)-Evolution and environment: 73-107. Yale Uni this concept involves the Rhyniopsida as the versity Press, New Haven. progenitors of Protolepidodendrales which later on Banks HP, Bonamo PM & Grierson JD 1972. Leclereqia complexa evolved into Lepidodendrales and from thence to gen. et sp. nov., a new lycopod from the late Middle Devonian of eastern New York. Rev. Palaeobot. Palyno/. Pleuromeiales and Isoetales, on one hand, and 14 19-40 Selaginellales on the other (Te>"'1-figure 2) Recent Banks HP & Davis MR 1969_ Crenaticaulis, a new genus of interpretation of the variously lobed fertile and Devonian plants allied to Zosterophyllum, and its bearing sterile microphylls in diverse Protolepidodendrales on the classification of early land plants. Am. I Bot. 56 as 3-dimensional telome trusses (Schweitzer, 1980; 436449 Bierhorst OW 1971. i\lIorphoiogy of vascular plants_ Macmillan, Bonamo & Grierson, 1981) lends credence to the New York. concept of rhyniopsid ancestry of protolepidoden Bock W 1962. A study of fossil Isoetes_ I Paleont. 36 53·59. drids. Further, the possibility that Zosterophyllop­ Bonamo PM & Grierson JD 1981. Leaf variation in Leclereqia sida itself could have probably originated from complexa and its possible significance. Bot. Soc_ Am. Misc. Rhyniopsida merits serious consideration, as Ser. 160 42. Bower FO 1935. Primitive land plants. Macmillan, London. indicated by the discovery of Renalia blleberi Brack·Hanes SO 1978. On the megagametophytes of two lepido­ (Gensel, 1976) in the Lower Devonian, furnishing dendracean cones. Bot. Gaz. 139 140·146. tantalizing evidence for the pathway leading to Brown RW 1958. New occurrences of the fossil quillwons called stalked lateral sporangia with distal dehiscence. Isoetiles. I Washington Acad Sci. 48 358-361. [n conclusion, it appears that Drepanophycales Chaloner WG 1968. The cone of Cyclostigma kiltorkense Hough· ton, from the Upper Devonian of lreland. I Linn. Soc_ Bot. and Protolepidodendrales constitute a constellation 61 2536 of Devonian lycopods from which the remaining Dele"oryas TO 1962. Morphology and evolution of fOSSil plants. lycopods evolved along two different lines, viz., Holt, Rinchart & Winston, New York. Lycopodiales from Drepanophycales, and DiMichele WA & Phillips TL 1985. Arborescent lycopod reproduc­ tion and paleoecology in a coal-swamp environment of Late Lepidodendrales, Pleuromeiales, Isoetales and Middle Pennsylvanian age (Harrin coal, Illinois, U.S.A) Selaginellales from protolepidodendralean stock. Rev. Palaeobot. Palyno/' 44 1-26. Triassic Pleuromeia, and Cretaceous Nathorstiana Eggert DA & Kanemoto NY 1977 Stem phloem of a Middle Pen· could represent the products of e),,'1reme reduction nsylvanian Lepidodendron Bot. Gaz. 108 102-111. from Sigillaria-like Upper Carboniferous-Permian Fairon·Demaret M& Banks HP 1978. L.eaves of Archaeosigillaria vanuxemii, a Devonian lycopod from New York. Am. I Bor. arborescent lycopods. As regards Isoetales, however, 65 246249 it now appears fairly convincing that this group Gensel PG 1975. A new species of Sawdonia with notes on the originated from small Lepidodendron-like plants origin of microphylls and lateral sporangia. Am. I Bot. 136 : with basal cormose rhizophore by further 50·62. diminution. Gensel PG 1976. Renalia hueberi, a new plant from the Lower Devonian of Gaspe. 22 :_ 19-37. All available data indicate in no uncertain Rev. Palaeobot. Palyno/' Jennings JR 1975. Protostigmaria, a new plant organ from the manner that the lyCdpods which appeared in the Lower Mississippian of Virginia. Palaeontology 18 19-24. Lower Devonian, radiated and multiplied through Kramer KU & Green PS 1991. The families and genera of vascular the Upper Devonian reaching their peak of evolution plants, 1. Pteridophytes and Gymnosperms. Narosa during the Upper Carboniferous-Permian, but Publishing House, New Delhi. declined drastically since then, have not given rise Magdefrau K 1956. Pa(aobiologie der Pflanzen G. Fischer, Jena. Meyen SV 1987. Fundamentals of palaeobotany. Chapman & Hall, to any other group of Tracheophyta and hence London. constitute a "Blind Alley". PhillipS TL 1979. Reproduction of heterosporous arborescent lycopods in the Mississippian-Pennsylvanian of Euramerica. Rev. Palaeobot. Palyno/' 27 : 239-289. REFERENCES Pigg KB & Rothwell GW 1979. Stem-shoot transition of an Upper Pennsylvanian woody lycopsid. Am_ I Bot. 66 914-924. Abbott ML 1963. Lycopod fructifications from the Upper Freeport Ramanujam CGK & Stewart \'qN 1969- A Lepidocarpon cone tip (No. 7) cool in southeastern Ohio. Palaeontographica 8112 : from the Pennsylvanian of Illinois. Palaeontographica 93·118. 8127 159-167. Andrews HN 1961. Studies in paleobotany. John Wiley, New York. Schumaker-Lambry J 1966. Etude d'un cone de Lepidocarpaceae Balbach MK 1962. Observations on the ontogeny of Lepidocarpon. du houiller beIge Achlamydocarpon belgicum gen. et sp. Am. I Bot. 49 984-989. nov. Acad R. Belg Sci. 17 : 6-27. Banks HP 1960. Notes on Devonian lycopods. Senckenberg leth. Schweitzer HJ 1980. Ueber Taeniophyton devonicus and 41 5988 Cladoxylon scoparium aus dem Mittledevon von Wuppenal. RAMANUJAM-ORIGIN AND EVOLUTION OF LYCOPODS 57

Palaeontographica 8173 : 1·25. biology. McGraw·Hill, New York. Sporne KR 1966. The morphology of pteridophytes. Hutchinson Thomas BA 1978. Carboniferous Lepidodendraceae and Lepido· Universiry Library, London. carpaceae. Bot. Rev. 44 : 321· 364. Stewart WN 1983. Palaeobotany and evolution of plants. Cam· Zimmermann W 1952. Main results of the "Telome Theory". Pala· bridge Universiry Press, Cambridge. eobotanist 1 : 456· 470. Taylor TN 1983. Paleobotany: an introduction to fossil plant