Abstract
The extant taxa Ephedra, Gnetum and Welwitschia were earlier placed in a single order, Gnetales, and a single family, Gnetaceae. These three taxa (considered to be the highest evolved among the gymnosperms) lack fossil record except for the remains of pollen of Ephedra from the Eocene (54 my B.P.), and pollen-like remains of Ephedra and Welwitschia from the Permian (280 my B.P.) (Delevoryas 1962). Certain common features of these taxa are comparable to angiosperms: (a) vessels are present in the wood, (b) the microsporangia and ovules are borne on fertile shoots which form compound strobili, (c) the ovules are enclosed within one or two envelopes, in addition to the integument and (d) the upper part of the inner integument extends into a long tubular structure, the micropylar tube.
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© 1997 Springer-Verlag Berlin Heidelberg
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Biswas, C., Johri, B.M. (1997). Gnetopsida. In: The Gymnosperms. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-13164-0_17
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DOI: https://doi.org/10.1007/978-3-662-13164-0_17
Publisher Name: Springer, Berlin, Heidelberg
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