Gymnosperm systematics and phylogeny: A reply to commentaries by C. B. Beck,C. N. Miller,and G. W. Rothwell

This paper is a reply to commentaries by Beck (1985), Miller (1985), and Rothwell (1985) on the author’s paper on basic features of gymnosperm systematics and phylogeny (Meyen, 1984). The author reasserts that his proposal to recognize three classes of gymnosperms—Ginkgoopsida, Cycadopsida, and Pinopsida—is in better agreement with the currently available paleobotanical data. The affinities of the orders Arberiales, Pentoxylales, gigantopterids, Calamopityales, and Ephedrales with the Ginkgoopsida are but tentative. The most important remaining question?etermining the understanding of relations between Ginkgoopsida and Pinopsida—concerns primary vs. secondary platyspermy in each class, and this question can be answered only by obtaining fuller information on (1) cupular or non-cupular seeds in the oldest Ginkgoopsida, and (2) the vascularization of nucellus in the oldest Pinopsida. Theoretical premises of the author’s taxonomic and phylogenetic decisions are explained.     

Gymnosperm Phylogeny — A commentary on the views of S. V. Meyen

In his important contribution to the literature on gymnosperm phylogeny, “Basic Features of Gymnosperm Systematics and Phylogeny as Evidenced by the Fossil Record,” Meyen (1984) uses the classical comparative method of the morphologist and the “congregational” method, i.e., grouping by common characters, of the taxonomist. The latter may have led him to categorize some taxa on the basis of superficially similar, non-homologous characters because he used no apparently objective method to distinguish homoplasy. For this and other reasons, Meyen’s hypothesis of evolutionary relationship among gymnosperms cannot, at present, be accepted as any nearer the truth than several competing proposals. The major innovation of Meyen’s proposed phylogeny is the recognition of the clade, Ginkgoopsida, coordinate with Cycadopsida and Pinopsida. Ginkgoopsida encompasses Calamopityaceae, Callistophytales, Glossopteridales, Peltaspermales, Caytoniales, and Ginkgoales, among others. These taxa are considered to be related because, in Meyen’s view, they share the common character of primary platyspermy — i.e., the presumed platyspermic seed-type of the basal group, Calamopityaceae, is considered to have evolved directly from the pteridophytic condition of an ancestral form. This basis for Ginkgoopsida is weakened by the facts that no seeds have been discovered in organic connection with any calamopityacean and, except for the poorly-preserved seed-like structure,Spermolithus, all seeds that occur earlier in the geologic record than fossils of the Calamopityaceae are radiospermic. It is possible, therefore, that even if the platyspermic seed,Lyrasperma, found in association with the calamopityacean,Stenomyelon, were borne by that plant, it is secondarily platyspermic, having evolved from a radiospermic ancestor. The foundation upon which Ginkgoopsida was erected seems, therefore, to be rather tenuous. Other characters used by Meyen, both reproductive and vegetative are discussed. Some which he considers significant, are interpreted to be unimportant in denoting phylogeny, while others are interpreted to support alternative hypotheses. Meyen proposes that the Ginkgoopsida evolved from archaeopterid progymnosperms. This viewpoint seems to be based largely on his erroneous belief thatArchaeopteris was probably a seed plant that bore compound leaves. There is no definitive evidence that supports the view thatArchaeopteris bore seeds. On the other hand, there is strong evidence to support the contention thatArchaeopteris produced simple leaves (Carluccio et al., 1966; Beck, 1971), not compound leaves. Meyen’s phylogenetic proposal is based on data that can be and, in part, have been differently interpreted by others. Consequently, it deserves the careful and critical evaluation of all students of gymnosperm phylogeny.     

Recent advances on phylogenomics of gymnosperms and a new classification

Living gymnosperms comprise four major groups: cycads, Ginkgo, conifers, and gnetophytes. Relationships among/within these lineages have not been fully resolved. Next generation sequencing has made available a large number of sequences, including both plastomes and single-copy nuclear genes, for reconstruction of solid phylogenetic trees. Recent advances in gymnosperm phylogenomic studies have updated our knowledge of gymnosperm systematics. Here, we review major advances of gymnosperm phylogeny over the past 10 years and propose an updated classification of extant gymnosperms. This new classification includes three classes (Cycadopsida, Ginkgoopsida, and Pinopsida), five subclasses (Cycadidae, Ginkgoidae, Cupressidae, Pinidae, and Gnetidae), eight orders (Cycadales, Ginkgoales, Araucariales, Cupressales, Pinales, Ephedrales, Gnetales, and Welwitschiales), 13 families, and 86 genera. We also described six new tribes including Acmopyleae Y. Yang, Austrocedreae Y. Yang, Chamaecyparideae Y. Yang, Microcachrydeae Y. Yang, Papuacedreae Y. Yang, and Prumnopityeae Y. Yang, and made 27 new combinations in the genus Sabina.     

Seed ferns from the late Paleozoic and Mesozoic: Any angiosperm ancestors lurking there?

Five orders of late Paleozoic-Mesozoic seed ferns have, at one time or another, figured in discussions on the origin of angiosperms, even before the application of phylogenetic systematics. These are the Glossopteridales, Peltaspermales, Corystospermales, Caytoniales, and Petriellales. Although vegetative features have been used to suggest homologies, most discussion has focused on ovulate structures, which are generally interpreted as megasporophylls bearing seeds, with the seeds partially to almost completely enclosed by the megasporophyll (or cupule). Here we discuss current information about the reproductive parts of these plants. Since most specimens are impression-compression remains, homologizing the ovulate organs, deriving angiospermous homologues, and defining synapomorphies remain somewhat speculative. Although new specimens have increased the known diversity in these groups, a reconstruction of an entire plant is available only for the corystosperms, and thus hypotheses about phylogenetic position are of limited value. We conclude that, in the case of these seed plants, phylogenetic analysis techniques have surpassed the hard data needed to formulate meaningful phylogenetic hypotheses. Speculation on angiosperm origins and transitional stages in these fossils provides for interesting discussion, but currently it is still speculation, as the role of these groups in the origin of angiospermy continues to be cloaked in Darwin's mystery.     

On the Current Classification System of Paleozoic Seeds

This paper summarizes the history of classifications of Paleozoic seeds and revaluates the previous classification systems of Paleozoic detached seeds. The current status of studies on Paleozoic. gymnosperms: has been deteched seeds and whole fossil gymnosperms indicates that Seward’s classification system for Paleozoic seeds inadequate since all the seeds of Cardiocarpales in his system are not cordaitean female reproductive organs as Seward’s suggested. It is shown from investigations of whole fossil plants that the members of Cardiocarpales were derived from at least three different major groups of Paleozoic gymnosperms. Moreover, Meyen’s suggestion that the gymnosperms be classified based on symmetry of seeds has been little supported since all the fossil gymnosperms have not shown structurally preserved seeds and organic attachment. In order to relate detached seeds to whole fossil gymnosperms, the present author suggests that five families: Lagenostomaceae, Pachytestaceae, Callospermariaceae, Cryptospermaceae and Cardiocarpaceae be established for Paleozoic seeds and the Order Trigonocarpales be renamed as Pachytestales since the genus Trigonocarpus does not now include structurally preserved seeds. Thus, the five families may be considered either as subdivisions of the three orders of detached seeds: Lagenostomales, Pachytestales and Cardiocarpales, or as female reproductive organs of whole fossil gymnosperms of the five Permo-Carboniferous major groups: Lyginopteridales, Medullosales, Callistophytales Gigantopteridales and Cordaitales. A Key to Paleozoic seeds is provided as follows: A. Seeds with a cupule; integument thin, simple, deeply lobed and less differentiated;nucellus united to integument up to the base of pollen chamber; pollen chamber complex ................................. Lagenostomales, Lagenostomaceae A. Seeds without a cupule; integument thick, complex, unlobed and differentiated into several layers; nucellus free within integument except at the base; pollon chamber simple ................................................................................................ B B. Seeds radially symmetrical in shape; integumentary bundles present; nucellus bundles typical ................................................... Pachytestales, Pachytestaceae B. Seeds bilaterally symmetrical in shape; integumentary bundles present or absent; nucellus bundles often untypical .................................... C (Cardiocarpales) C. Bundles absent in integument; main bundle C-shaped in transverse section with a sclerenchyma bundle ............................................ Cryptospermaceae C. Bundles present in integument; main bundle not C-shaped in transverse section without a sclerenchyma bundle ......................................................... D D. Seeds very small with secretory cavities in integument; nucellus bundles limited in nucellus platform .......................................... Callospermariaceae D. Seeds large without secretory cavities in integument; nucellus bundles limited in nucellus platform or not ....................................... Cardiocarpaceae     

Axial nature of the cupule‐bearing organ in Caytoniales

Abstract Caytoniales are an important group of seed plants, and the nature of their female reproductive organ may influence interpretations of the seed plant phylogeny and the origin of angiosperms. Although not convincingly demonstrated by clear evidence, cupules on previously described specimens were interpreted as being distichously arranged, implying that the cupule‐bearing organ in Caytoniales was a pinnate megasporophyll. Here a female reproductive organ of Paracaytonia hongtaoi gen. et sp. nov. (Caytoniales) is reported from Liaoning, China. The well preserved specimen clearly shows a spiral arrangement of cupules along the reproductive axis, suggesting that the cupule‐bearing organ in Caytoniales is not a megasporophyll but a branch. This new information on the axial nature of the cupule‐bearing organ in Caytoniales has significant implications on the placement of Caytoniales in the seed plant phylogeny and interpretation of the relationship between Caytoniales and angiosperms.     

Application of the Serological Method for Evaluation of Relations between Gymnospermous and Dicotyledonous Plants

An attempt has been undertaken to evaluate interrelations of gymnospermous and dicotyledonous plants on the basis of immunochemical studies of seed proteins. For this purpose, 12 antisera were raised to proteins of taxa representing four gymnosperm classes: Ginkgoopsida, Cycadopsida, Coniferopsida, and Gnetopsida. Seed proteins of eight dicotyledonous subclasses (after Takhtadzhyan, 1987) were used. The representatives of all dicotyledonous subclasses gave immunochemical reactions with those of all gymnospermous classes. The data obtained suggest the presence of sufficiently close immunochemical relations between gymnosperms and dicotyledons. Samples were found among the representatives of subclasses Dilleniidae, Hamamelididae, and Rosidae, which gave satisfactory reactions with eight to ten antisera to proteins of dicotyledonous seeds. Analysis of the data we obtained suggests that gymnospermous and dicotyledonous plants took their origin from a common pragymnospermous ancestor and later evolved independently or that dicotyledons separated from gymnosperms at an early stage of their evolution before divergence of the latter into several phyletic lineages.     

A critical review of S. V. Meyen’s “Basic features of gymnosperm systematics and phylogeny as evidenced by the fossil record”

Meyen’s “Basic features of gymnosperm systematics and phylogeny as evidenced by the fossil record” departs from the usual Botanical Review article that provides the botanical community with a synthesis of the state of knowledge and understanding of an individual segment of botany, i.e., an interpretation of progress in a specialty for the nonspecialist. Instead, this article appears intended to challenge paleobotanists to reconsider traditional views of the interrelationships of the various gymnospermous groups and the concepts on which they were based. A classification scheme is presented which divides gymnosperms into the Ginkgoopsida, Cycadopsida and Pinopsida. These classes are based on Meyen’s analysis of the structural variation in gymnosperms and his interpretation of homologies of various organs. Too often, however, key plants are reconstructed from parts known only in association and relationships are tied to assumptions of homology that have yet to be documented. The result has value in providing a succinct summary of gymnospermous structure and variation in the different groups. It is also commendable in its attempt to explain and use concepts and terminology designed especially for gymnosperms. This critique shows that in many cases there are alternative interpretations that also fit the evidence.     

Distinguishing angiophytes from the earliest angiosperms: A Lower Cretaceous (Valanginian-Hauterivian) fruit-like reproductive structure

A remarkably diverse Lower Cretaceous (Valanginian-Hauterivian) flora at Apple Bay, Vancouver Island, preserves seed plants at an important time of floristic evolutionary transition, about the same time as the earliest flowering plant megafossils. The fossils are permineralized in carbonate concretions and include tetrahedral seeds within cupule- or carpel-like structures. These enclosing structures, composed of elongate sclerenchyma cells with spiral thickenings that grade externally to a few layers of parenchyma, are vascularized by one collateral vascular bundle and lack trichomes. They apparently broke open to release the tightly enclosed seeds by valves. Seeds are similar to those of the Triassic seed fern Petriellaea, but are about 100 million years younger and differ in size, vascularization, integumentary anatomy, seed attachment, and number of seeds/cupule. These new seeds are described as Doylea tetrahedrasperma gen. et sp. nov., tentatively assigned to Corystospermales. Inverted cupules are reminiscent of an outer angiosperm integument rather than a carpel. Like fruits, cupules opened to release seeds at maturity, thereby foretelling several aspects of angiospermy. They show that nearly total ovule enclosure, a level of organization approaching angiospermy, was achieved by advanced seed ferns during the Mesozoic.     

A new Late Cretaceous ginkgoalean reproductive structure Nehvizdyella gen. nov. from the Czech Republic and its whole-plant reconstruction

During the Mesozoic Era, gingkoaleans comprised a diverse and widespread group. Here we describe ginkgoalean fossils in their facies context from the Late Cretaceous (Cenomanian) Peruc-Korycany Formation of the Czech Republic and present a reconstruction of tree architecture and ecology. Newly described in this study is the ovuliferous reproductive structure, Nehvizdyella bipartita gen. et sp. nov. (Ginkgoales). This ovuliferous organ consists of a bifurcating axis, terminated by large cupule-like structures, probably homologous to the collar of the recent Ginkgo. Each cupule encloses an orthotropous ovule. In specimens with the early developmental stages preserved, the entire ovule and young seed, with the exception of the micropylar area, is embedded in the cupule. Mature seeds consist of sclerotesta and sarcotesta. Monosulcate pollen grains of Cycadopites-type are found adhering to the seeds. Although similar to Ginkgo in terms of its large size and reduced number of seeds, N. bipartita differs from the extant genus in having ovules completely enclosed in a cupule-like structure. The co-occurrence of N. bipartita with ginkgoalean leaves of Eretmophyllum obtusum (Velenovsky) Kva?ek, J., ginkgoalean short shoots of Pecinovicladus kvacekii Falcon-Lang, and ginkgoalean trunk wood of Ginkgoxylon gruettii Pons and Vozenin-Serra in monodominant taphocoenoses at four geographically distant localities suggests that these remains all belong to one plant. This is supported by the close morphological and anatomical similarity between the different organs. Facies analysis of plant assemblages indicates that our Cretaceous tree occupied a water-stressed coastal salt marsh environment. It therefore represents the first unequivocal halophyte among the Ginkgoales.     

Seed plant phylogeny and the origin of angiosperms: An experimental cladistic approach

We present a numerical cladistic (parsimony) analysis of seed plants plus progymnosperms, using characters from all parts of the plant body, outgroup comparison, and a method of character coding that avoids biases for or against alternative morphological theories. The robustness of the results was tested by construction of alternative trees and analysis of subsets of the data. These experiments show that although some clades are strongly supported, they can often be related to each other in very different but nearly equally parsimonious ways, apparently because of extensive homoplasy. Our results support Rothwell’s idea that coniferopsids are derived fromCallistophyton- like platyspermic seed ferns with saccate pollen, but the hypothesis that they evolved fromArchaeopteris- like progymnosperms and the seed arose twice is nearly as parsimonious. Meyen’s division of seed plants into radiospermic and primarily and secondarily platyspermic lines is highly unparsimonious, but his suggestion that ginkgos are related to peltasperms deserves attention. Angiosperms belong among the platyspermic groups, as the sister group of Bennettitales,Pentoxylon, and Gnetales, and this “anthophyte” clade is best related toCaytonia and glossopterids, although relationships with other combinations of Mesozoic seed fern taxa are nearly as parsimonious. These results imply that the angiosperm carpel can be interpreted as a modified pinnate sporophyll bearing anatropous cupules (=bitegmic ovules), while gnetalian strobili are best interpreted as aggregations of highly reduced bennettitalian flowers, as anticipated by Arber and Parkin and Crane. Our most parsimonious trees imply that the angiosperm line (though not necessarily all its modern features) extended back to the Triassic, but a later derivation of angiosperms from some species ofCaytonia or Bennettitales, which would be nearly as parsimonious, should also be considered. These results raise the possibility that many features considered key adaptations in the origin and rise of angiosperms (insectpollinated flowers, rapid reproduction, drought tolerance) were actually inherited from their gymnospermous precursors. The explosive diversification of angiosperms may instead have been a consequence of carpel closure, resulting in increased speciation rates due to potential for stigmatic isolating mechanisms and/or new means of dispersal. DNA sequencing of extant plants and better information on anatomy, chemistry, sporophyll morphology, and embryology of Bennettitales and Caytoniales and the morphological diversity of Mesozoic anthophytes could provide critical tests of relationships.     

Contributions to the knowledge of the Caytoniales

Some additional features of the caytonialean capsule are described and the conventional interpretation of the “mouth” is challenged. The Caytonanthus pollen grains examined in the light and scanning electron microscope show a bilobed equatorial saccus sculptured with endosexinous ridges. The caytonialean seeds and androclads (Caytonanthus tyrmensis sp. nov.) from the uppermost Jurassic—lowermost Cretaceous Tyrma locality (Far East of the U.S.S.R.) are closely comparable with the corresponding organs of their Middle Jurassic predecessors showing striking evolutionary conservatism. However, the evolutionary potentials of the Caytoniales must not be understood. The caytonialean monandra and monogyna are considered as the nearest approach to angiosperm stamens and pistils.     

Leaf evolution in Southern Hemisphere conifers tracks the angiosperm ecological radiation

The angiosperm radiation has been linked to sharp declines in gymnosperm diversity and the virtual elimination of conifers from the tropics. The conifer family Podocarpaceae stands as an exception with highest species diversity in wet equatorial forests. It has been hypothesized that efficient light harvesting by the highly flattened leaves of several podocarp genera facilitates persistence with canopy-forming angiosperms, and the angiosperm ecological radiation may have preferentially favoured the diversification of these lineages. To test these ideas, we develop a molecular phylogeny for Podocarpaceae using Bayesian-relaxed clock methods incorporating fossil time constraints. We find several independent origins of flattened foliage types, and that these lineages have diversified predominantly through the Cenozoic and therefore among canopy-forming angiosperms. The onset of sustained foliage flattening podocarp diversification is coincident with a declining diversification rate of scale/needle-leaved lineages and also with ecological and climatic transformations linked to angiosperm foliar evolution. We demonstrate that climatic range evolution is contingent on the underlying state for leaf morphology. Taken together, our findings imply that as angiosperms came to dominate most terrestrial ecosystems, competitive interactions at the foliar level have profoundly shaped podocarp geography and as a consequence, rates of lineage diversification.     

Was the ANITA rooting of the angiosperm phylogeny affected by long-branch attraction? Amborella, Nymphaeales, Illiciales, Trimeniaceae, and Austrobaileya

Five groups of basal angiosperms, Amborella, Nymphaeales, Illiciales, Trimeniaceae, and Austrobaileya (ANITA), were identified in several recent studies as representing a series of the earliest-diverging lineages of the angiosperm phylogeny. All of these studies except one employed a multigene analysis approach and used gymnosperms as the outgroup to determine the ingroup topology. The high level of divergence between gymnosperms and angiosperms, however, has long been implicated in the difficulty of reconstructing relationships at the base of angiosperm phylogeny using DNA sequences, for fear of long-branch attraction (LBA). In this study, we replaced the gymnosperm sequences from the five-gene matrix (mitochondrial atp1 and matR, plastid atpB and rbcL, and nuclear 18S rDNA) used in our earlier study with four categories of divergent sequences--random sequences with equal base frequencies or equally AT- and GC-rich contents, homopolymers and heteropolymers, misaligned gymnosperm sequences, and aligned lycopod and bryophyte sequences--to evaluate whether the gymnosperms were an appropriate outgroup to angiosperms in our earlier study that identified the ANITA rooting. All 24 analyses performed rooted the angiosperm phylogeny at either Acorus or Alisma (or Alisma-Triglochin-Potamogeton in one case due to use of a slightly different alignment) and placed the monocots as a basal grade, producing genuine LBA results. These analyses demonstrate that the identification of ANITA as the basalmost extant angiosperms was based on historical signals preserved in the gymnosperm sequences and that the gymnosperms were an appropriate outgroup with which to root the angiosperm phylogeny in the multigene sequence analysis. This strategy of evaluating the appropriateness of an outgroup using artificial sequences and a series of outgroups with increments of divergence levels can be applied to investigations of phylogenetic patterns at the bases of other major clades, such as land plants, animals, and eukaryotes.     

An overview of fossil Ginkgoales

Neither direct fossil evidence nor consensus exists on the origin of the Ginkgoales and their phylogenetic relationships with other seed plants. The bases for assigning most Palaeozoic leaf fossils to Ginkgoales are shaky. There are eight morphogenera considered more or less well defined and useful for classifying Mesozoic leaf and shoot compressions/impressions, and only two or three morphotaxa of anatomically preserved wood fossils have generally been used. About nine genera of ovulate organs, however, have been reported in the Mesozoic. Whole plant reconstructions suggested for a number of well-preserved ginkgoalean plants are enumerated. Their associated (or connected) organs, and their occurrences and distributions are cited in detail. There are three or four major evolutionary lineages so far recognized among Mesozoic Ginkgoales: the Ginkgo-Grenana-Nehvizdyella lineage, the Karkenia lineage, the Yimaia-Toretzia/Umaltolepis lineage and perhaps the Schmeissneria lineage. Ginkgoales may be classified into five to six families, with a number of accessory morphotaxa and unclassified taxa. The general evolutionary trend among ginkgoaleans is reduction of both vegetative and reproductive organs. The reduction trend is seen clearly in the genus Ginkgo and roughly recapitulated in the developmental sequences of the living species. A similar reduction sequence runs in parallel in other lineages of Ginkgoales. Ginkgoales flourished during Jurassic and Early Cretaceous, but a significant radiation of the group had occurred already in Late Triassic when Ginkgoales were present in high taxonomic diversity and showed considerable morphological innovation. Geographically, Ginkgoales are mainly distributed in Laurasia and probably originated there. The earliest records are from Laurasia as is the relict living fossil. Ginkgoales may have lived in various climates and diverse habitats, although most flourished in mesic and temperate climates, and the Late Cretaceous and Cenozoic ginkgos were largely confined to riparian environments.Advances in micro- and ultrastructure studies and chemical investigations on the cuticle and megaspore membrane of ginkgoalean fossils are also summarized. Further studies in these fields may provide useful information on the ecology and palaeoclimatology of Ginkgoales as well as their taxonomy.     

Evolution of Reproductive Organs in Land Plants

LEAFY gene is the positive regulator of the MADS-box genes in flower primordia. The number of MADS-box genes presumably increased by gene duplications before the divergence of ferns and seed plants. Most MADS-box genes in ferns are expressed similarly in both vegetative and reproductive organs, while in gymnosperms, some MADS-box genes are specifically expressed in reproductive organs. This suggests that (1) the increase in the number of MADS-box genes and (2) the subsequent recruitment of some MADS-box genes as homeotic selector genes were important for the evolution of complex reproductive organs. The phylogenetic tree including both angiosperm and gymnosperm MADS-box genes indicates the loss of the A-function genes in the gymnosperm lineage, which is presumably related to the absence of perianths in extant gymnosperms. Comparison of expression patterns of orthologous MADS-box genes in angiosperms, Gnetales, and conifers supports the sister relationship of Gnetales and conifers over that of Gnetales and angiosperms predicted by phylogenetic trees based on amino acid and nucleotide sequences. Received 30 July 1999/ Accepted in revised form 9 September 1999     

New perspectives on the Mesozoic seed fern order Corystospermales based on attached organs from the Triassic of Antarctica

A new Triassic corystosperm is described from the Shackleton Glacier region of Antarctica. The compression fossils include cupulate organs (Umkomasia uniramia) and leaves (Dicroidium odontopteroides) attached to short shoot-bearing branches. The cupulate organs occur in groups near the apices of the short shoots, and each consists of a single axis with a pair of bracts and a subapical whorl of five to eight ovoid cupules. This unique architecture indicates that the cupules are individual megasporophylls rather than leaflets of a compound megasporophyll. A branch bearing an attached D. odontopteroides leaf provides the first unequivocal evidence that Umkomasia cupulate organs and Dicroidium leaves were produced by the same plants. Although this had previously been assumed based on organ associations, the new specimens are important in demonstrating that a single species of corystosperm produced the unique cupulate organs described here and the geographically and stratigraphically widespread and common D. odontopteroides leaf. Therefore, biostratigraphic, paleoecological, and phylogenetic studies that treat Dicroidium leaf morphospecies as proxies for biological species of entire plants should be reconsidered. Phylogenetic analysis suggests that the corystosperm cupule is an unlikely homologue for the angiosperm carpel or outer integument.     

Is the anthophyte hypothesis alive and well? New evidence from the reproductive structures of Bennettitales

Bennettitales is an extinct group of seed plants with reproductive structures that are similar in some respects to both Gnetales and angiosperms, but systematic relationships among the three clades remain controversial. This study summarizes characters of bennettitalean plants and presents new evidence for the structure of cones and seeds that help clarify relationships of Bennettitales to flowering plants, Gnetales, and other potential angiosperm sister groups. Bennettitales have simple mono- or bisporangiate cones. Seeds are borne terminally on sporophylls. They have a unique structure that includes a nucellus with a solid apex, no pollen chamber, and a single integument, and they are clearly not enclosed by a cupule or other specialized structures. Such features differ substantially from Gnetales, flowering plants, and the seed fern Caytonia, providing no compelling evidence for the origin of the angiospermous carpel. Cladistic tests were performed to assess the strength of the "anthophyte hypothesis" and possible relationships of Bennettitales, Gnetales, and Caytonia to flowering plants. Our results do not support the anthophyte hypothesis for the origin of angiosperms by a transformation of fertile organs that were already aggregated into a cone or flower-like structure. However, the anthophyte topology of the seed plant tree continues to be supported by morphological analyses of living and extinct taxa.     

Middle Albian gymnosperms from the Río Martín Valley (Teruel,Spain)

The fossil-rich site within the Albian Escucha Formation in the Oliete Sub-basin, located in the Northeast of Spain, has provided a great abundance of impressions, including leave remains and seed cones of Coniferales (Sphenolepis kurriana, Sphenolepis sternbergiana, Elatides curvifolia, Brachyphyllum sp. and Geinitzia sp. cf. G. rigida), leaves of Caytoniales (Sagenopteris elliptica), Ginkgoales (Ginkgoites pluripartita, and Sphenobaiera sp. cf. S. longifolia), Bennettitales (Ptilophyllum sp. cf. P. pecten and aff. Zamites sp.), Cycadales (Nilssonia tenuinervis and Ctenozamites with entire and denticulate pinnae margins), Czekanowskiales, and reproductive structures of Gnetales. The gymnosperm remains are fairly abundant in the upper member, built up of sediments deposited in fluvial and swamp environments without marine influence. The different gymnosperm associations in this outcrop indicate a wide variety of environments in a subtropical climate, and a mixture of North American and European taxa in the Iberian plate during the Middle Albian.