The Pa!aeobotallist, 28·29: 413-422, 1981. TRIPHYLETIC EVOLUTION OF VASCULAR PLANTS KAZUO ASAMA National Science Museum (Natural History Museum), 3-23-1 Hyakunin-cho Shinjuku-ku, Tokyo-l60, Japan. ABSTRACT Permian Shansi flora reveals the relation between the change of plants and the environments which is shown in the principles of Growth Retardation (abbreviated G. R.). The changes of plants in Palaeozoic, Mesozoic and Cenozoic are all explained by the principles of G. R., not by the principles of Growth Acceleration, which means that the environments in geological age must have been changed to the more and more unsuitable environments for the growth of plants. These environmental changes in• dicate the paleoclimatic change of increasing annual range of temperature. To adapt to these climatic changes the plants might have to change successively their form and function through geological age. We call these changes - evolution. Therefore the plants might have to change their form and function grading up from spore-stage (pteridophyte) to angiosperm-stage through gymnosperm-stage. Palaeozoic pteridophytes have three lineages, namely, Lycopsida (have microphyll), Sphenopsida (have articulate stem) and Pteropsida (have macrophyll). The plants of these three lineages in Palaeozoic must have been changed paraIIeIIy their form and function grading up from spore-stage to angiosperm-stage through ages. Therefore it is reason• able to recognize the evolution of three lineages, Microphyta,Arthrophytaand Macrophyta. Key-words - Triphyletic evolution, Pteridophytes, Microphyta, Arthrophyta, Macro• phyta, Japan. 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Recently the author pub• lished three books and discussed about "Origin1974, oftheangiospermsauthor wroteinferreda paperfrom the evolution of plants in detail (Asama INthe evolution of leaf form" and 1975; Asama & Kimura, 1977; Asama: stated that the origin of angiospermous 1979a). 'H3 414 THE PALAEOBOTANIST EVOLUTION OF SHANSI FLORA AND Plants must have attained their full growth PRINCIPLES OF GROWTH RETARDATION in a mild oceanic climate. But as the I studied the Permian plants from Shansi, climate turned continental, their growth China which had been described earlier was retarded, and their size was diminished. by Halle (1927) in detail and observed the Consequently, various changes occurr.ed in following evolutionary series in Shansi their leaf form. Fusion and enlargement flora (Asama, 1959): were particularly significant changes. A. Emplectopteris Series (Text-fig. 1,Principle The principles of G.R., based on the A, Fusion): Emplectopteris triangularis evolution of leaf form of the plants in the - Gigantonoclea lagrelii - Bicoem• Cathaysia flora, are very important because plectopteris hallei - Tricoemplectopteris they indicate that the environmental changes taiyuanensis . are closely related to the leaf form changes. B. Emplectopteridium Series (Text-fig. 1, Therefore the principles ought to be applic• Principle A, Fusion): Emplectopteri• able to any geological ages and regions. dium alatum - Bicoemplectopteridium By correlating the leaf form changes in a longifolium - Gigantopteris nicotianae• given geological age with the principles, folia the environmental change of that period C. Konnoa Series (Text-fig. 1, Principle causing the leaf transformation can be in• B, Enlargement); Konnoa penchihuensis ferred. .And, conversely, by determining - Cathaysiopteris whitei the envIronmental changes of a certain D. Alethopteris Series (Text-fig. 1, Principle region from certain phenomena (such as B, Enlargement and Principle E, Shor• appearance of glaciers, arid climate, etc.), tening-palmation): Alethopteris norinii we can infer resultant changes of leaf - Protoblechnum wongii - Psygmo• form in that region. phyllum multipartitum I have examined the leaf form changes E. Tingia Series (Text-fig. 1, Principle B, in various geological ages and found that Enlargement): Tingia partila - T. car• all changes can be explained by the principles bonica - T. crassinervis of Growth Retardation, without a single F. Trizygia Series (Text-fig. 1, Principle case in fav0ur of Growth Acceleration B, Enlargement): Trizygia oblongifolia (G.A.). This means that the environ• - T. speciosa - T. sinocoreana - T. ment of the geological ages responsible for grandifolia the leaf form changes gradually worsened. G. Lobatannularia Series (Text-fig. 1, To interpret this, the writer assumed that the Principle B, Enlargement): Lobatannu• environmental change of the geological ages laria sinensis - L. lignulata - L. was a climatic change in which the annual heianensis range gradually increased (Asama, 1960, Through these processes of evolution, 1962, 1975, 1979a, 1979b) (see Text-fig. 8). the plants changed their leaf forms. And I have classified these type of processes THREE LINEAGES OF VASCULAR PLANTS into seven groups in terms of Principles of Growth Retardation, abbreviated G.R. Palaeozoic pteridophytes are classified (Text-fig. 1). ifoltoPsi10phytopsi.da, Lycopsida, Sphenop• The changes explained by the principles SIda and Pteropsida by the characteristics ibove occurred when the plants became of leaves or stems such as naked stem mic• smaller (Text-fig. 1), by growth retardation rophyll, articulate stem and macr~phyll showing the terminal abbreviation of on• respectively. Psilophytopsida consists of togeny (the loss of late stage) (Asama, Rhyniaceae, Zosterophyllaceae, Psilophyta• 1962' Takhtajan, 1969) and these principles ceae and Asteroxylaceae. But Sporne may' be called the principles of neoteny (1975) thinks that Asteroxylaceae belongs (Asama 1960, 1979a). The cause of such to Lycopsida and I am also of the same change; among the plants of the Cathaysia opinion. Psilophytopsida, except Astero• flora can be found by examining the xylaceae, is not the ancestral type of all palaeogeography of the region. In the vascular plants but only that of Pteropsida. Cathaysia region the environment changed Therefore there had been the plants of three a mild oceanic climate to a continental types, Lycopsida, Sphenopsida and Pterop• climate by the upheaval of continent. sida in the Early Devonian. ASAMA - TRIPHYLETIC EVOLUTION OF VASCULAR PLANTS 415 Dicotyledon Monocoty.l~dol\ (Palma.) . IIDnocotyle4on (Cramin •• ) t. ~ Si ze reduction IS -)0 .,,, Vertleilla tion ~18~_~ WI9 ---+ 20 21 -) ~l~7 22 PRINCIPlE'i~F, lNOENTATlCt'l~~!~~PRINCIPLE G,tDECURRENCY PiMa d<!currency TEXT-FIO.1 - Principles of Growth Retardation (Principles of G. R.) (adapted from Asama, 1960 1962 1975). A great part of changes found in fossil plants through ages, Palaeozoic, Mesozoic and Cenozoic ~ilI b~ explained by these principles indicating that the environments change successively mild to severer, simple to more complex through geological ages. Therefore the paleoclimatic change shown in Text-fig. 8 was speculated. Plants of the geological age changed plained by principles of Growth Retardation. regularly their leaf forms in response to Therefore we must recognize that such the environmental change in where they characteristics as microphyll, macrophyll live. And their changes are always ex- and artIculate stem are the inherent 416 THE PALAEOBOTANIST H & U Paleozoic Mesozoic Cenozoic .•. ". o E j" 3' Reeeat!~ Coni (ers Recent .Lycopodiales Poleozoio Lepldod~ndroles TEXT-FIG. 2 - Phylogeny of Microphyta (Asama, 1975). Showing the progressive and regressive evolution. characters of each lineage and that these to Microphyta, if they have the leaves characteristics have never been lost in recent derived from microphylls. Reversely even plants showing each lineage. Therefore I though plants have small type of leaves have classified the vascular plants into three th;::yar~ plants belonging to Macrophyta, if lineages, Microphyta (Lycopsida and its they hav~ the leaves derived from macro· descendants), Macrophyta (Pteropsida and phylls. The relation between the leaf size its descendants) and Arthrophyta (Sphenop• and lineage is very important. The plants sida and its descendants). The plants of having large type of leaves are not always these three lineages have been evolved, plants belonging to Macrophyta and those parallelly from the stage of spore to the having sml11 type of leaves are not always stage of angiosperms through that of gymno• plants belonging to Microphyta. Sometimes sperms as shown in Text-figures 2, 3 and 4. plants of Microphyta and Macrophyta may In general, the leaves of Microphyta and have articulate stem caused by shortening Arthrophyta are microphylls showing s!llall of stem (Text-fig. 1, Principle E, Shortening• type of leaves but they s~ow sometlJ~es Verticillation). But they do not belong large type of leaves gather~ng.