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Journal ArticleDOI

The appearance of gymnospermous structure

01 Aug 1970-Biological Reviews (Blackwell Publishing Ltd)-Vol. 45, Iss: 3, pp 379-399
TL;DR: The appearance, primarily within this group of plants, of three major aspects of gymnospermous vegetative structure: the secondary wood, the leaf, and the primary vascular system are considered.
Abstract: During Devonian time, as diversification of psilophytes, lycopsids, sphenopsids and ferns was taking place and these groups were evolving into clearly definable taxa, another major group, the progymnosperms (Beck, 1960u, b, 1962a), was also becoming established as a dominant element of the flora. This group first becomes clearly recognizable in Middle Devonian strata. By Upper Devonian time it had acquired many of the important characteristics of gymnosperms. The progymnosperms are of great significance because they seem to be the immediate ancestors of seed plants (Beck, 1960b, 1962a, 1964a, 1966; Meeuse, 1963; Banks, 1968). In this paper I shall consider the appearance, primarily within this group of plants, of three major aspects of gymnospermous vegetative structure: the secondary wood, the leaf, and the primary vascular system.
Citations
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Journal ArticleDOI
TL;DR: The results raise the possibility that many features considered key adaptations in the origin and rise of angiosperms were actually inherited from their gymnospermous precursors, and the morphological diversity of Mesozoic anthophytes could provide critical tests of relationships.
Abstract: 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.

506 citations

Journal ArticleDOI
TL;DR: It is widely believed that fossils are of fundamental importance in reconstructing phylogeny and "fossils provide the soundest basis for evolutionary classification", but it is often noted that conclusions are necessarily tenuous in their absence.
Abstract: It is widely believed that fossils are of fundamental importance in reconstructing phylogeny (e.g. 24, 28). Simpson (52, p. 83), for example, argued "fossils provide tl?,e soundest basis for evolutionary classification." Although phylogenies of many groups have been reconstructed using morphological or chemical characters of extant organisms alone, it is often noted that fossils would have been of great use in clarifying relationships and that conclusions are necessarily tenuous in their absence. Thus, Thorne (58, p. 85) commented 431 0066-4170/90/0101/0431 $02.00 Annual Reviews www.annualreviews.org/aronline

429 citations


Cites background from "The appearance of gymnospermous str..."

  • ...In fact, better understanding of Paleozoic "progymnosperms" and "seed ferns" refutes the concept hat the angiosperm conditions are ancestral (2, 10, 11)....

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Journal ArticleDOI
TL;DR: Comparisons of dated pollen floras of other regions indicate that one major subgroup of angiosperms, tricolpate-producing dicots (i.e., excluding Magnoliidae of Takhtajan) originated in the Aptian of Africa-South America at a time of increasing aridity and migrated poleward into Laurasia and Australasia.
Abstract: Morphological, stratigraphic, and sedimentological analyses of Early Cretaceous pollen and leaf sequences, especially from the Potomac Group of the eastern United States, support the concept of a Cretaceous adaptive radiation of the angiosperms and suggest pathways of their initial ecological and systematic diversification. The oldest acceptable records of angiosperms are rare monosulcate pollen grains with columellar exine structure from probable Barremian strata of England, equatorial Africa, and the Potomac Group, and small, simple, pinnately veined leaves with several orders of reticulate venation from the Neocomian of Siberia and the basal Potomac Group. The relatively low diversity and generalized character of these fossils and the subsequent coherent pattern of morphological diversification are consistent with a monophyletic origin of the angiosperms not long before the Barremian. PatuxentArundel floras (Barremian-early Albian?) of the Potomac Group include some pollen and leaves with monocotyledonous features as well as dicotyledonous forms. Patuxent angiosperm pollen is strictly monosulcate and has exine sculpture indicative of insect pollination. Rare Patuxent-Arundel angiosperm leaves are generally small, have disorganized venation, and are largely restricted to sandy stream margin lithofacies; the largest are comparable to and may include ancestors of woody Magnoliidae adapted to understory conditions. Patapsco floras (middle to late Albian?) contain rapidly diversifying tricolpate pollen and several new complexes of locally abundant angiosperm leaves. Ovate-cordate and peltate leaves in clayey pond lithofacies may includeancestors of aquatic Nymphaeales and Nelumbonales. Pinnatifid and later pinnately compound leaves with increasingly regular venation which are abundant just above rapid changes in sedimentation are interpreted as early successional “weed trees” transitional to but more primitive than the modern subclass Rosidae. Apparently related palmately lobed, palinactinodromous leaves which develop rigidly percurrent tertiary venation and become abundant in uppermost Potomac stream margin deposits (latest Albian-early Cenomanian?) are interpreted as riparian trees ancestral to the order Hamamelidales. Comparisons of dated pollen floras of other regions indicate that one major subgroup of angiosperms, tricolpate-producing dicots (i.e., excluding Magnoliidae of Takhtajan) originated in the Aptian of Africa-South America at a time of increasing aridity and migrated poleward into Laurasia and Australasia. However, the earlier (Barremian) monosulcate phase of the angiosperm record is represented equally in Africa-South America and Laurasia before marked climatic differentiation between the two areas. These trends are considered consistent with the hypothesis that the angiosperms originated as small-leafed shrubs of seasonally arid environments, and underwent secondary expansion of leaf area and radiated into consecutively later successional stages and aquatic habitats after entering mesic regions as riparian “weeds,” as opposed to the concept that they arose as trees of mesic forest environments.

419 citations

Journal ArticleDOI
TL;DR: These five extant groups were embedded in the derived half of a morphologically diverse spectrum of extinct taxa that strongly influenced tree topology and elucidated patterns of acquisition of morphological character-states, demonstrating that pteridosperms and other more derived “stem-group” Gymnosperms are critical for understanding seed-plant relationships.
Abstract: Hilton J. (School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK) and R. M. Bateman (Natural History Museum, Cromwell Road, London, SW7 5BD, UK). Pteridosperms are the backbone of seed-plant phylogeny. J. Torrey Bot. Soc. 133: 119–168. 2006.— Using Doyle (1996) as a starting point, we compiled a morphological cladistic matrix of 54 coded taxa (31 wholly extinct, and 23 at least partly extant) and 102 informative characters in order to explore relationships among gymnosperms in general and pteridosperms in particular. Our core analysis omitted six supplementary fossil taxa and yielded 21 most-parsimonious trees that generated two polytomies in the strict consensus tree, both among pteridosperms; the first affected several hydraspermans, and the second affected the three peltasperm/ corystosperm taxa analyzed. The resulting topology broadly resembled topologies generated during previous morphological cladistic analyses that combined subs...

272 citations


Cites background from "The appearance of gymnospermous str..."

  • ...In addition, they test the controversial Beck hypothesis of a diphyletic origin of seed plants (Beck 1957, 1970, 1971, 1976, 1981), which contrasts most starkly with the Rothwell hypothesis of seedplant monophyly (Rothwell 1982, 1986, Rothwell and Scheckler 1988, Rothwell and Serbet 1994)....

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Journal ArticleDOI
TL;DR: An integrated system of morphological concepts for gymnosperm fructifications is introduced, which does not lean upon any system existing for other higher plants, and Comparative analytical treatment of all available characters of the most thoroughly studied fossil genera provided the foundation for an ordered ranking of congregations.
Abstract: This paper introduces an integrated system of morphological concepts for gymnosperm fructifications, which does not lean upon any system existing for other higher plants. Comparative analytical treatment of all available characters of the most thoroughly studied fossil genera provided the foundation for an ordered ranking of congregations, each unit being assigned to the status of families, orders and classes. The transformation of the generative and vegetative organs has been traced along various phylogenetic branches. A new large phylogenetic branch (class Ginkgoopsida), beginning with the Lower Carboniferous Calamopityales, has been established. The lineage evolved from this order to Callistophytales and further to Peltaspermales. The family Peltaspermaceae encompasses, among others, plant types formerly regarded as ginkgoaleans. The orders Ginkgoales, Leptostrobales (Czekanowskiales) and Caytoniales evolved from the Peltaspermales. The order Arberiales (glossopterids) evidently evolved from the Calamopityales. In the lineage from Calamopityales to Ginkgoales a common seed type is conserved (platyspermic, non-cupular with two vascular bundles in the integument). Radiospermic seeds are conserved in the class Cycadopsida. In the lineage from Lagenostomales to Trigonocarpales the radially symmetrical cupule underwent modification into an integument of the same type of symmetry. The earliest Lagenostomales with the bilaterally symmetrical cupule evolved into the Cordaitanthales, where the cupule, also undergoing modification, was transformed into a bilaterally-symmetrical integument. In Cordaitanthales and their descendents the Pinales the seeds became secondarily platyspermic (in contrast to the primary non-cupular and primary platyspermic seeds in Ginkgoopsida); their vascularization was progressively reduced. These two orders are grouped into the class Pinopsida. It is believed that angiosperm seeds are in effect radiospermic with a radial cupule, their vascularization also being progressively reduced. If this holds true, the angiosperm ancestry should be sought in the class Cycadopsida. The Caytoniales, Arberiales, Peltaspermales, Leptostrobales and other orders of the class Ginkgoopsida should be excluded from the stock of probable angiosperm ancestors. A new gymnosperm phylogeny has been proposed and the evolution of the phylogenetic branches outlined in terms of the phytochoria system of the geological past. The basic evolutionary innovations took place within the Equatorial Belt and adjacent ecotone areas. Three types of processes, often underrated, have a paramount role in gymnosperm phylogeny. They are defined as follows: (1) homoeotic transformations of organs; corresponding to them are heterotopies, in the morphological aspect, and saltations, in the evolutionary sense; (2) dedifferentiation of the organs (the shift of one ontogenetic program onto various organs); (3) transitive polymorphism (conservation in diversity of a certain organ during phylogeny). These processes probably serve to indicate that rearrangement in the functions of the regulatory genes played an important role in the evolution of gymnosperms.

225 citations

References
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Journal ArticleDOI
TL;DR: The existence of such a group of pteridophytic plants, of possible psilophytic origin, obviously not ferns, showing unmistakeable gymnosperm characters, and which preceded any known gymnosperms in time, eliminates the necessity to consider any group of f Ferns, known or unknown, as ancestors of the Gymnosperms.
Abstract: A specimen from the late Devonian Katsberg beds of Delaware County, New York, comprising a pyritized axis determined asCallixylon and leaves determined asArchaeopteris, is described and illustrated. The leaves are probablyA. macilenta Lesquereux and the axisC. zalesskyi Arnold, but because of doubt of the specific identity of the leaves a nomenclature transfer is delayed.

137 citations

Journal ArticleDOI
TL;DR: It is suggested that Actinopodium, Svalbardia and Siderella are related closely to Archaeopteris and that this group of genera shows evolutionary stages in webbing of leaves and planation of branch systems.
Abstract: from which leaf traces arise in a spiral sequence. The anatomy of the "rachis" and of the "'pinnae" is shown to be similar to that of the stem, Callixylon, which bore these "fronds." Branching, epidermal pattern and stomates are described for the spirally arranged leaves (fertile pinnules). Attachment and dehiscence of sporangia as well as their stomates are reported. Archaeopteris is retained in the Class Progymnospermopsida which includes plants with gymnospermous anatomy and pteridophytic reproduction. It is suggested that Actinopodium, Svalbardia and Siderella are related closely to Archaeopteris and that this group of genera shows evolutionary stages in webbing of leaves and planation of branch systems. The opportunities for ontogenetic studies of the arborescent genus Archaeopteris are pointed out.

72 citations