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About Mesozoic Pteridophylls

Walter Zimmermann
American Journal of Botany
Vol. 56, No. 7, Special Issue: XI International Botanical Congress Held at the University of Washington (Aug., 1969), pp. 814-819
Stable URL: http://www.jstor.org/stable/2440603
Page Count: 6
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About Mesozoic Pteridophylls
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Abstract

Two types of pteridophylls are very common in the Mesozoic era: the Polypodium and the Dipteridaceae. The Polypodium-type formed by pendulous overtopping is represented in the Mesozoic era by the form-genus Cladophlebis, in the Paleozoic era by the form-genus Pecopteris, and today by Dryopteris. Overtopping differs in these three pteridophylls. Nearly all Paleozoic pteridophylls show a catadromic structure. Today pteridophylls with anadromic and combined catadromic/anadromic structures are the dominant ones. The Mesozoic genera demonstrate a transitional structure: catadromic structures are still frequent, but equally frequent are combined catadromic/anadromic structures. Pteridophylls solely with anadromic structures are unknown in the Mesozoic era. The Dipteridaceae-type is almost exclusively Mesozoic. It is primitive in the dichotomy of the rachis, but advanced in that it is net-veined. Thus the Mesozoic pteridophylls represent connecting links between Paleozoic and recent leaf-types. This nature of Mesozoic pteridophylls can be understood only on the basis of the telome theory.

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