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Classification of Gymnosperms from the Viewpoint of Paleobotany
Chester A. Arnold
Vol. 110, No. 1 (Sep., 1948), pp. 2-12
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/2472553
Page Count: 11
You can always find the topics here!Topics: Plants, Gymnosperms, Fossils, Leaves, Conifers, Seeds, Botany, Fructification, Ferns, Inflorescences
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It should be realized that origin is the ultimate basis of relationships, and the known facts of the history of plant groups should take precedence over superficial structural resemblances in determining them. Mere resemblances are often the result of parallel development. Groups of characters as expressed by vegetative as well as by reproductive structures should be utilized in defining the larger categories such as divisions and classes. It is necessary that classification schemes be revised frequently and kept abreast of modern knowledge. Obsolete classifications retard progress and become misleading. The fossil record indicates that the Cycadophyta and Coniferophyta are separate developmental lines that are distinct from each other as far into the past as they can be traced. The oldest known coniferophytes belong to the Pityeae, which were large trees during Upper Devonian times. The Pityeae were succeeded in the Upper Carboniferous by the Cordaiteae from which the Coniferales were probably derived during the late Paleozoic. The late Paleozoic (Permian) also witnessed the departure of the Ginkgoales from the ancestral cordaitean stock. The Cycadophyta show evidence of fern ancestry. The earliest recognizable pteridosperms appear in the Lower Carboniferous and the oldest cycads in the late Paleozoic. The origin of the Cycadeoidales, Ephedrales, and Gnetales is not clear. An altered scheme of classification of the vascular plants is proposed in which the "gymnosperms" are parceled among three classes in accordance with affinities as suggested by their origin.
Botanical Gazette © 1948 The University of Chicago Press