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Some comments on the origin and evolution of

Article in Canadian Journal of · October 1981 Impact Factor: 1.4 · DOI: 10.1139/b81-254

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All in-text references underlined in blue are linked to publications on ResearchGate, Available from: R. A Stockey letting you access and read them immediately. Retrieved on: 09 July 2016 Some comments on the origin and evolution of conifers1

RUTHA. STOCKEY Department of Botany, University of Alberta, Edmonton, Alta., Canada T6G 2E9 Received December 16, 1980 STOCKEY,R. A. 1981. Some comments on the origin and evolution of conifers. Can. J. Bot. 59: 1932-1940. During the last several years there has been an increased emphasis on the study of evolution including various aspects of their reproductive biology. The occurrence of similar stelar features as well as trends in the evolution of reproductive structures still point to cordaitalean affinities for the Coniferales. The evolutionary history of such families as the , , and Taxodiaceae is beginning to be elucidated as well as that of certain extinct families including the Cheirolepidaceae and the Voltziaceae. Systematic investigations of fossil cone vasculature and resin canal distribution, leaf cuticles, seed integuments, and embryo structure not only have increased our knowledge of conifer evolution but also have led to changes in our views on the systematics of extant conifer groups.

Introduction Beck (1970, 1971, 1975) and others (Scheckler 1978; In the last few years there has been an increased Scheckler and Banks 1971) have noted that characters emphasis on the study of conifer evolution. Since the common in conifer xylem are present in the Late pioneering work of Rudolf Florin from the 1920's to the among the progymnosperms. This relation- early 1960's (Lundblad and Malmstrom 1966) much has ship, however, has been questioned by Rothwell(1975) been learned about the evolution and reproductive biol- on the basis of primary vasculature. The group, how- ogy of these organisms. The presence of similar mor- ever, that most paleobotanists regard as the oldest in the phological and anatomical characters, in combination coniferophyte line is the Cordaitales. These are with comparative studies of the reproductive structures, mostly and in age. still indicates possible cordaitalean affinities for the Cordaites, now known to have been a more diverse conifers. Our knowledge of primitive conifer groups, group than once thought (Whiteside 1974), may have however, has been expanded in recent years as a result of reached 30 m in height and bore large strap-shaped investigations by a great number of workers. leaves up to 1 m long. They bore their reproductive The purpose of this paper is to review some thoughts structures in loose stobili called inflorescences. The with respect to conifer origins and consider how these inflorescences (Cordaianthus) are monosporangiate, For personal use only. have changed since the time of Florin, and to discuss bearing either ovules or pollen sacs. The inflorescence some ideas dealing with the early evolution of certain consists of an axis with two or four rows of bracts fossil and modem conifer families. The main emphasis (Rothwell 1977; Daghlian and Taylor 1979). In the axil will be comparative morphology of the reproductive of each bract is a short shoot or dwarf shoot with structures. helically arranged scales. Pollen cones have from four to The plants we know as coniferophytes (Coniferophy- six pollen sacs borne at the tip of each scale. Recently, a tina) are currently divided into three orders: Voltziales, new cordaitean pollen organ has been described from Taxales, and Coniferales. Of these three orders, the Kentucky; Gothania lesliam Daghlian and Taylor Voltziales, sometimes called the transition conifers, are (1979) contains pollen referable to the dispersed spore thought to be ancestral to other conifer groups. Their genus Felixipollenites, while the pollen cones of Cor- geologic range is Pennsylvanian to . The daianthus contain grains of the Florinites type (Millay Taxales, represented by five living genera, have a fossil and Taylor 1974). The ovulate cones or inflorescences record extending back to the L~werJurassic and (also Cordaianthus) exhibit radially symmetrical short continuing to the recent. The third order, the Conifer- shoots in the axils of bracts. Ovules attached to the short Can. J. Bot. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 11/15/14 ales, has fossil representatives by the period. shoot are stalked, orthotropous, and roughly heart The Coniferales are divided into six or seven families: shaped. Araucariaceae, , , Taxo- diaceae, Pinaceae, , and Palissyaceae. Voltziales The Cupressaceae and Taxodiaceae are sometimes put During the time that cordaites flourished (Carboni- into one large family (Eckenwalder 1976). ferous-Permian) the voltzialean conifers are also present paper was presented in a symposium entitled ~~d-in the fossil record. In current classification schemes the mark Events in the Evolution of Plants, co-sponsored by the Voltziales contains three families: the Lebachiaceae, Canadian Botanical Association and the Canadian Association Voltziaceae, and . The imbricate, of Palynologists at Carleton Unive'rsity on June 21, 1979. needlelike foliage of some of these conifers (Lebachia, 0008-40261811101932-09$01.00/0 01981 National Research Council of CanadalConseil national de recherches du Canada STOCKEY 1933

Walchia) looked similar to that of living Araucaria ceae. The structure of the integuments too, with an heterophylla (Mirb.) Franco, the Norfolk Island pine. In extensive system of tightly compacted sclereids as general, members of the Lebachiaceae had more com- described by Schweitzer (1963) is similar to some of the pact cones than the cordaites. Lebachia has one erect living and fossil araucarians (Stockey 1975, 1978). ovule that is borne terminally on each radially symmet- In addition to these genera there are a large number of rical short shoot in the axil of a bifurcate bract (Fig. 1). other conifers in the Voltziaceae that all show bilaterally Another genus in this family, Ernestiodendron, has three symmetrical, reduced short shoots, or flattened lobed to seven ovules per short shoot; and the scales or sterile scales in the axils of bracts. Aethophyllum from the elements of the short shoot are few to none in different Triassic of France has recently been placed in the species of the genus (Fig. 3). The ovules are either erect Voltziales by Grauvogel-Stamm and Grauvogel (1975). or inverted. There is, in addition, a noted difference in Young plants, pollen and seed cones, and foliage are symmetry of the short shoot which is flattened or known. There are five sterile lobes and five inverted bilaterally symmetrical (Florin 1951). Both Lebachia ovules in the axil of a bract (Fig. 7). are and Ernestiodendron are Upper to Lower known to have epigeal and two . Permian in age. Both juvenile and mature foliage are known for the A recent discovery from the Permian of Texas (Miller genus that is now considered by Grauvogel-Stamm and Brown 1973) has expanded our knowledge about the (1978) to belong to its own family. The ovulate cones diversity of reproductive structures within the Lebach- are most closely compared with Cryptomeria D. Don iaceae. The ovulate cone of Moyliostrobus texanum and the fossil Swedenborgia Nathorst. Miller and Brown combines several features of Le- Another interesting Triassic genus Cycadocarpidium, bachia and some of those of Ernestiodendron (Fig. 2). also redescribed by Grauvogel-Stamm (1978), has One seed per scale and numerous sterile scales per short cones up to 30 mm in length with cone-scale complexes shoot are like those found in Lebachia. The bilaterally inserted nearly at right angles to the axis. The ovulifer- symmetrical short shoot is similar to the cones of ous scale is trilobed (each lobe coming to a fine point) Ernestiodendron. fused to and borne in the axil of a long (11 mm) In addition to these types of reproductive structures lanceolate bract (Fig. 8). There are usually two to three there are a large number of late Paleozoic vegetative inverted seeds per scale that are roughly rectangular in remains that are unlike those of Lebachia or Ernestio- shape with lateral wings and resemble seeds of Sciado- dendron. One of these is Carpentieria frondosa pitys or Taiwania of the Taxodiaceae. (Goepp.) Florin (Fig. 4) from the Lower Permian, the Florin documented several intermediate stages be- For personal use only. lateral shoot system of which resembles "the walchias" tween the short shoot or dwarf shoot of cordaites and the (Florin 1951). Leaves of this are bifurcate and may ovuliferous scale of conifers. Changes that have taken indicate that the entire conifer leaf has arisen from the place involve: the general reduction of the inflorescence forked type by reduction. axis, a flattening to the short shoot, a fusion of the sterile Members of the family Voltziaceae have been used by parts of the dwarf shoot, fusion of the ovule axis to the Florin to show intermediate stages between the Le- scale, and eventual elimination of the ovule axis, total bachiaceae and modern conifers. Pseudovoltzia (Per- reduction in the number of fertile parts, and the mian age), recently reinvestigated by Schweitzer reduction in number of ovules from many to few. There (1963), has a bilaterally symmetrical short shoot in the has also been a change in ovule position from ortho- axil of a bract with five sterile lobes that are fused to the tropous to anatropous in some conifer groups. It is bract at their bases (Fig. 9). There are three stalked important to note that Cordaianthus and early forms ovules, the stalks fused to the short shoot. The number such as Lebachia and Ernestiodendron occur in rocks of of ovules and degree of fusion of the lobed scales to the the same age. Pseudovoltzia and Ullmannia also occur bract have led Schweitzer (1963) to suggest Pseudo- during the same period. These genera do, however, Can. J. Bot. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 11/15/14 voltzia as an ancestor of the Taxodiaceae. indicate that general trends such as these listed above Another Permian genus, Ullmannia, recently rede- have taken place in the coniferophyte line through scribed by Schweitzer (1963), has one recurvedovule on geologic time. Most workers still maintain the belief the upper surface of a large flattened scale in the axil of a that the conifer cone-scale or ovuliferous scale is homo- bract. It is not known whether the ovule was fused to the logous to a short shoot or dwarf shoot of Cordaianthus. scale or attached by a stalk. Ullmannia shows that as The third family in the Voltziales is the recently early as the Permian conifer cones were very modified recognized Cheirolepidaceae that is best known from the (Florin 1951). The one-seeded condition of the cone- Late Triassic-Cretaceous of Europe and Argentina scale complex (bract and ovuliferous scale or bract and (Archangelsky 1966, 1968; Alvin and Pais 1978; Rey- short shoot) is characteristic of cones in the Araucaria- manowna and Watson 1976) and recently from the CAN. 1. BOT. VOL. 59, 1981 For personal use only. Can. J. Bot. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 11/15/14

FIGS. 1-9. Reconstructions of fossil conifers. Fig. 1. Lebachia piniformis, cone-scale complex. Fig. 2. Moyliostrobus texanum, cone-scale complex. Fig. 3. Emestiodendron~liciforme,cone-scale complex. Fig. 4. ~hr~entieriafrondosa. Fig. 5. Hirmerella muensteri, ovulate cone. Fig. 6. Hirmerella muensteri (=Cheirolepis muensteri) after shedding of ovuliferous scales. Fig. 7. Aethophyllum stipulare, cone-scale complex. Fig. 8. Cycadocarpidium pilosum, cone-scale complex. Fig. 9. Pseudovoltzia liebeana, cone-scale complex. Ovules stippled in Figs. 1-3; b, bract; s, short shoot or dwarf shoot. All figures redrawn from: Figs. 1, 3, 4, Florin 1951; Fig. 2, Miller and Brown 1973; Figs. 5, 6, Jung 1968; Figs. 7, 8, Grauvogel-Starnrn 1978; Fig. 9, Schweitzer 1963. STOCKEY 1935

U.S.A. (Daghlian and Person 1977). 'The best known Examination of cones of Pararaucaria and those of genus is Hirmerella, recently reexamined by Jung genera in the Cheirolepidaceae would seem to indicate (1967, 1968). A number of cones from the Late Triassic that the number of ;eeds per scale is probably an to Early of Europe were found attached to and insignificant character for taxonomic purposes for coni- associated with foliage similar to that of some of the fers living during the Mesozoic. Takhtajan (1953) Voltziaceae. Ovulate cones in this family shed their and others have suggested that the Taxodiaceae and lobed ovuliferous scales while bracts remained attached Pinaceae have a common origin. The intermediate to the cone axis. One cone genus Cheirolepidium position of Pararaucaria may lend some support to this Takhtajan (=Cheirolepis Schimper) was found to be a conclusion. Pararaucaria should probably be placed in later developmental stage of the cones of Hirmerella its own family of the Coniferales. Further work on (Figs. 5, 6). The whole plant Hirmerella has now been Jurassic age conifers will provide the 'opportunity of reconstructed by Jung (1968) as a large arborescent placing Pararaucaria in the proper perspective with conifer. Pollen cones had two pollen sacs per micro- respect to the other conifer families. sporophyll. Pollen grains belong to the dispersed spore genus Classopollis Pflug. The deciduous scales have Coniferales 6-10 distal lobes and each bears two seeds (Fig. 5). Fossil members belonging to the Pinaceae have These features and comparative wood anatomy have recently been reviewed by Miller (1976, 1977). The prompted Jung to suggest taxodiaceous affinities. Pinaceae is the largest modem family and apparently the The Lower Cretaceous genus Tomaxellia from most recently evolved. The first bona fide pinaceous Argentina also bore deciduous scales (Archangelsky fossil cones are those of the genus Pinus and have been 1966, 1968). Both ovulate and pollen cones are known described by Alvin (1960) from the Lower Cretaceous of with in situ Classopollis pollen. Belgium. Prior to this time no fossils are known with Classostrobus Alvin, Spicer and Watson (1978) is a enough internal structure to assign them with certainty to newly described Classopollis-containing cone from the the Pinaceae. Isle of Wight, the cuticle of which closely compares There has recently been a report of an interesting with Pseudofrenelopsis parceramosa (Fontaine) Wat- conifer from the Upper Triassic of North Carolina. son (1977) thus linking groups of foliage taxa (Frenel- Compsostrobus neotericus Delevoryas and Hope (1973) opsis, Pseudofrenelopsis) with the Classopollis- had two seeds per scale and unlobed ovuliferous scales producing Cheirolepidaceae. that may have been partially fused to the bracts. Pollen Another fossil cone thought by some to belong to the cones have also been found bearing two pollen sacs and For personal use only. Cheirolepidaceae is the genus Pararaucaria from the bisaccate pollen (Alisporites). Even though first exami- Jurassic of Argentina (Fig. 12). Cones of Pararaucaria nation of these compression fossils showed pinelike patagonica, however, do not show lobed cone-scale features, Miller (1976) feels that Compsostrobus is too complexes like Hirmerella or Tomaxellia but a thick incompletely known internally to place it for certain in ovuliferous scale that is partially fused to the smaller the Pinaceae. woody bract. There is one and sometimes two winged Pseudoaraucaria is a well-known extinct genus that ovules per scale and the seeds, not the scales, were has been reported in Cretaceous deposits of Europe by probably shed at maturity (Stockey 1977). In cone Alvin (1957a, 19576) and recently by Miller and tangential sections there is a massive abaxially concave Robison (1975) from the United States. Pseudoarau- scale trace that departs from the axis stele; below it is the caria has two seeds per cone-scale complex. There is a large circular bract trace. These two are accompanied by prominent ridge of tissue (interseminal ridge) that two groups of sclereids that are triangular in outline. separates the two ovules and usually overarches them This type of vascularization is most similar to conifers of causing them to appear embedded in ovuliferous scale the Pinaceae; however, these do not usually have tissue like those of araucarians.

Can. J. Bot. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 11/15/14 massive bract traces (Miller 1976). Seeds with mature The second well-known fossil pinaceous genus is embryos have been found (Fig. 17) and there are from Pityostrobus. About 26 species have been described six to eight cotyledons per embryo. Cones of Pararau- from Europe and North America (Miller 1976). These caria combine a number of features characteristic of cones, although they are certainly pinaceous, share four to five families of conifers. One seed per scale is an characteristics of many of the living genera in the non- araucarian feature. Cone vascularization, seed wings, Pinus group of the family (e.g., Abies, Cedrus, Picea, numbers, and secondary xylem pitting are etc.). Recently a cone belonging to this group has been pinaceous. The woody bract and strong bract trace, found in the Lower Cretaceous McMurray Formation of cotyledon numbers, pith structure, and lack of resin Alberta (Stockey 1981). The cone is 13 cm long and canals in the xylem are taxodiaceous features. Seed externally resembles extant Picea. There are two integuments are like those of the Taxodiaceae and winged seeds per scale separated by a very small pad of Cupressaceae. tissue with one resin canal running the length of the pad. 1936 CAN. 1. BOT. VOL. 59, 1981

Vascularization of the cone-scale complex is unlike caria brownii, a new species from the Jurassic of En- Pinus but similar to other pinaceous genera. Pith gland (Stockey 1980b) and A. sphaerocarpa Carmthers structure is similar to Pseudolarix. The McMurray cone from the Jurassic of Somerset (Stockey 1980~).Arau- has one large resin canal that leaves the axis stele and caria sphaerocarpa was originally described (Carmthers extends out into the ovuliferous scale for 1 cm before it 1866) as a cone cast, but upon reexamination was found divides, and a large amount of internal sclerenchyma as to be well-preserved anatomically. The small pits or in cones of Pityostrobus hallii Miller (1974). scars on the bracts and scales indicate the positions of The Araucariaceae is a conifer family that can vascular bundles in the cone-scale complex. Seed probably be traced back to the Late Triassic. The family integuments are thick and composed of elongate, inter- has a southern hemisphere distribution today but had locking sclereids. Internal nucellar tissue, megagameto- fossil representatives in the northern hemisphere during phyte, and mature embryos are known. There is also a the Mesozoic. The genus Araucaria was present by the complex system of vascularization of the ovule chalaza. Jurassic. The genus is divided into four sections: Studies of these and other fossil araucarians indicate Columbea, Eutacta, Intermedia, and Bunya (Wilde and that not only is the genus Araucaria present by the Eames 1952). Many workers have suggested that the Jurassic but the major sections of the genus as well. section Bunya be abandoned since it contains only one Ancestors of the Araucariaceae will have to be sought in living species, A. bidwillii Hooker from Australia (Fig. much older sediments. Fossil evidence would seem to 10). Fossil evidence, however, would indicate the need indicate that we should retain the section Bunya even to retain the section. though it contains only one living species because there Araucaria mirabilis (Fig. 14) from the Cerro Cua- are many more fossil representatives in the past that drado Petrified Forest of Patagonia (Jurassic, Argentina) were much more widespread geographically. The sec- is most similar to A. bidwillii (Stockey 1975, 1978). tion Bunya may well be the most primitive within the Externally the bracts are large, woody, and winged genus. while the ovuliferous scales are small and partially fused to the underlying bracts (Figs. 10, 13, 14). There is one, Pollen cones inverted, sunken seed per scale (Figs. 13, 16). Seed One of the biggest unsolved problems in conifer integuments of mature cones reveal a sclerotesta com- evolution is the origin of pollen cones from a Cordai- posed of very densely packed elongate, branched anthus-type ancestor. An analogous evolutionary sclereids (Fig. 16). Seeds show remains of nucellus, scheme to that of ovulate cones does not appear to occur megagametophyte, and mature embryos with two coty- in the fossil record. Unlike the ovulate cones, pollen For personal use only. ledons (Figs. 11, 16). Smaller immature cones with cones of conifers are not regarded as compound, but ovules have also been found with immature seed simple strobili composed of helically arranged sporo- integuments, possible free nuclear megagametophyte, phylls and situated in the axil of a bract. and extended nucellar tissue (Stockey 1978). The It has been suggested (Wilde 1944) that each pollen prominent woody winged bracts, complex vasculature cone is equivalent to a short shoot of Cordaianthus of the seed chalaza, structure of the seed integuments, subtended by a bract (and thus equivalent to one two cotyledons per embryo, and wide separation of bract cone-scale complex of an ovulate cone). Recently, and scale place this cone in the section Bunya. however, Grauvogel-Stamm (1969, 1978) has suggest- Also associated with these cones are a number of ed that the cones of such cone genera as Darneya are small structures that look carrotlike or figlike. Upon actually compound structures in which the bract and close examination they appear similar to the seedlings of scale are fused. Sporangia of Darneya peltata Schaar- A. bidwillii (Fig. 15) that have swollen hypocotyls with schmidt et Maubeuge emend. Grauvogel-Stamm (1978) large amounts of stored starch and are borne on small branches on the adaxial surface of the (Stockey and Taylor 1978). cone-scale. Other cones, such as Willsiostrobus (the Can. J. Bot. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 11/15/14 Similar types of cone features are present in Arau- cone ofAethophyllum) do not show a supposed "ligne de

FIGS. 10-17. Living and fossil conifers. Fig. 10. Mature ovulate cone of Araucaria bidwillii showing large bracts and overlying ovuliferous scales. Arrow indicates ovuliferous scale. X0.45. Fig. 11. Transverse section of megagametophyte of Araucaria mirabilis with embryo. P13853 FMNH NO. 4. x42. Fig. 12. External surface of Pararaucaria patagonica. Orton 3 1219. x 2. Arrow indicates bract. Fig. 13. Isolated cone-scale complex of A. bidwillii showing one sunken ovule. X 0.45. Fig. 14. External surface of Araucaria mirabilis. Orton 3 1221C. X 2. Arrow indicates ovuliferous scale. of A. bidwillii showing swollen hypocotyl. X0.40. Fig. 16. Longitudinal section of mature seeds with embryos of A. mirabilis. P13939 No. 1. x 14. Fig. 17. Longitudinal section of cone of P. patagonica showing seeds with embryos. Orton 31217 No. 1. X3. a, axis; b, bract; e, embryo; h, hypocotyl; i, integument; m,megagametophyte; n, nucellus; o, ovule; os, ovuliferous scale. STOCKEY For personal use only. Can. J. Bot. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 11/15/14 CAN. J. BOT. VOL. 59, 1981

suture" and may, therefore, be simple structures. Fur- Triassic and thus overlap the earliest appearance of the ther fossil evidence, especially from permineralized modem conifer families in the fossil record. All of the material, may reveal the exact nature of this line of families of modem conifers, with the exception of the fusion. Cephalotaxaceae and perhaps the Pinaceae, appear to It has been suggested by Grau.voge1-Stamm (1978) have a possible Upper Triassic to Lower Jurassic appear- that the wide range of pollen cone types now being found ance (Miller 1977, p. 270). This has prompted Miller in Triassic deposits shows similarities to certain fems, (1977) to suggest that it is doubtful that modem families cordaites, and progymnosperms. Most fossils like evolved from the Voltziaceae that are mostly Late Willsiostrobus (=Masculostrobus) show abaxially Triassic to Jurassic in age, and that precursors should be directed pollen sacs, (Grauvogel-Stamm 1972; Grau- sought in Paleozoic to Early Triassic sediments. Some vogel-Stamm and Grauvogel 1973), while others like of the early records of the families are based on foliage Sertostrobus larus (Grauvogel-Stamm 1969) and Dar- alone, however, and are still disputed by some workers. neya peltata have adaxially directed pollen sacs on short The appearance of modem genera in the fossil record branches. It is interesting to note that in Grauvogel- indicates that the Araucariaceae, Taxodiaceae and Tax- Stamm's work (1978, Plate 24, Fig. 7) several pollen aceae contain probably the oldest genera known. By the cones of Aethophyllum were found on a large axis, each Jurassic not only is the genus Araucaria in existence, but on a short stalk in the axil of a bractlike structure. The the major sections of the genus as well (Stockey 1980b). ovulate cones of the plant are terminal on branches. Fossil evidence from cones such as A. mirabilis and A. sphaerocarpa would indicate that the extant section Concluding remarks Bunya should be retained even though it has only one Current ideas about the origin and evolution of living representative. This group was more widespread conifers are based mainly on the pioneering work of in the past and may be the most primitive type of Rudolf Florin. With the discovery of additional speci- araucarian. mens, some of his ideas have been challenged in recent The conifers in general were more numerous and years (Schweitzer 1963; Harris 1976; Grauvogel- more widespread in the past. New families have been Stamm 1978). There is evidence that progymnosperm erected for many of the newly discovered fossils. The anatomy is closely comparable to that of conifers (Beck Cheirolepidaceae which have seed cones with deciduous 1970, 197 1). The relationship, however, has recently scales and large persistent bracts are unlike any other been questioned on the basis of primary vasculature known conifers. With the discovery of pollen cones (Rothwell 1975). Comparative morphology of repro- (Tomarellia, Classostrobus) containing Classopollis For personal use only. ductive structures of the Cordaitales and their primary pollen and their associated foliage types (Frenelopsis, vasculature both show a close relationship between this Pseudofrenelopsis), the family is now better under- group and the conifers (Rothwell 1977). Recent studies stood. The Cheirolepidaceae appears to have been of the Cordaitales have also shown more diversity and widespread during the Mesozoic and its genera may specialization within the group than was known pre- have occupied a number of diverse habitats (Vakhra- viously (Whiteside 1974; Daghlian and Taylor 1979). meev 1970; Batten 1974; Alvin et al. 1978). Florin's ideas on the evolution of the conifer cone The cone of Pararaucaria patagonica shows that (1951) are the basis upon which further studies have another conifer group was present along with true been made. The evolution of the cone-scale complex araucarians during the Jurassic. These cones show from an axillary short shoot and subtending bract is similarities to those of four or five conifer families, documented by much fossil evidence. Steps in the especially the Taxodiaceae and Pinaceae, perhaps indi- evolution of an ovulate conifer cone from a cordaitean cating the two may be linked phylogenetically. strobilus include: a reduction in internode length, a The origin of the pollen cone in conifers is still a flattening of the short shoot, fusion of sterile parts of the difficult problem to resolve. Most fossils in the Triassic Can. J. Bot. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 11/15/14 short shoot, fusion of the ovule axis to the scale and like Compsostrobus, Masculostrobus spp., and Willsi- eventual elimination of this axis, total reduction in the ostrobus have pollen sacs on the abaxial surface of number of fertile parts, reduction in numbers of ovules, sporophylls, and therefore are nearly modem in appear- and in some cases a change in ovule position. Many ance by this time. Others like Darneya and Serto- genera described by Florin are being reinvestigated. As strobus, have adaxially positioned sporangia that are more evidence is found, genera such as Aethophyllum, clustered and may be attached to very small dichotomiz- Cycadocarpidium, Pseudovoltzia, and Ullmannia are ing axes. Some may, in fact be equivalent to one found to have ovules that are not stalked but fused to the cone-scale complex of an ovulate cone (Wilde 1944) scales like those of modem conifers (Grauvogel-Stamm while others may not (Grauvogel-Stamm 1978). 1978). Miller (1977) has pointed out that many of the At the present time further work is needed on plants intermediate voltzialean conifers are present in the within the Cordaitales and Progyrnnospermopsida so that their diversity and specialization are better understood. GRAUVOGEL-STAMM,L. 1969. Nouveaux types d'organes Only then can we get a clear picture of possible conifer reproducteurs mdles de Conifbres du Grbs a Voltzia (Trias ancestors. Not only have studies of fossil conifers added inferieur) des Vosges. Bull. Serv. Carte Geol. Alsace to our understanding of the extinct forms but they have Lorraine, 22: 93- 120. also had a direct influence on our classification of extant 1972. Revision de cBnes mdles du " infCrieurU taxa. With the discovery of additional fossil conifers in du Worcestershire (Angleterre) attribuCes a Masculostrobus willsi Townrow: Cornparaison avec des espbces voisines du late Paleozoic to early Mesozoic sediments we are Bundtsandstein supCrieur des Vosges (France). Palaeon- coming toward a closer understanding of their origin and togr. Abt. B Palaeophytol. 140: 1-26. subsequent radiation. Additional well-preserved Trias- 1978. La flore du Grbs i Voltzia (Bundtsandstein sic conifers will greatly expand our knowledge of the SupCrieur) des Vosges du Nord (France): Morphologie, diversity of coniferophytes, a group that probably was at anatomie, interpretations phylogCnetique et palCogCogra- its peak in diversity during the Mesozoic. phie. Sci. Geol. Univ. Louis Pasteur de Strasbourg, Inst. Geol. Mem. No. 50. pp. 1-225. ALVIN,K. L. 1957a. On the two cones Pseudoaraucaria GRAUVOGEL-STAMM,L., and L. GRAUVOGEL.1973. Masculo- heeri (Coemans) nov .comb., and Pityostrobus villerotensis strobus acurninatus nom.nov., un nouvel organe reproduc- nov.sp. from the Wealdon of Belgium. Mem. Inst. R. Soc. teur mdle de Gymnosperme du Grbs i Voltzia (Trias Nat. Belgium, 135: 1-27. infkrieur) des Vosges (France). Geobios, 6: 101-1 14. 19576. On Pseudoaraucaria Fliche emend., a genus 1975. Aethophyllurn Brongniart 1828, Conifbre (non of fossil pinaceous cones. Ann. Bot. (London), 21: 33-5 1. Equisetale) du Grbs i Voltzia (Bundtsandstein SupCrieur) 1960. Further conifers of the Pinaceae from the des Vosges (France) note preliminaire. Geobios, 8: Wealdon Formation of Belgium. Mem. Inst. R. Soc. Nat. 143-146. Belgium, 146: 1-39. HARRIS,T. M. 1976. The mesozoic gymnosperms. Rev. ALVIN,K. L., and J. J. C. PAIS. 1978. A Frenelopsis with Palaeobot. Palynol. 21: 119-134. opposite decussate leaves from the Lower Cretaceous of JUNG,W. 1967. Eine neue Reconstruktion des Fruchtzapfens Portugal. 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