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The Fossil History of the Gnetales

1996; University of Chicago Press; Volume: 157; Issue: S6 Linguagem: Inglês

10.1086/297403

1537-5315

Peter R. Crane,

Plant and animal studies

The fossil record of dispersed pollen documents that the extant genera Ephedra, Welwitschia, and Gnetum are the relictual extant remnants of a group of plants that was once more widespread and much more diverse. Unfortunately, macrofossils corresponding to these dispersed palynomorphs remain sparse, and only scattered information on other organs of fossil Gnetales are available Late Triassic and Early Jurassic fossils provide the most radical additions to knowledge of morphological diversity among probable extinct Gnetales, but more detailed information is needed to reliably and accurately establish their systematic affinities. In the long term, detailed morphological data from such fossils will be crucial for understanding morphological homologies between the reproductive structures of Gnetales and those of other plants. However, in the short term, studies of well-preserved material from Cretaceous mesofloras may be more informative Among the recent results of such studies has been the identification of small dispersed seeds with ephedroid pollen in the micropyle, and increased knowledge of the plants that produced the widespread and distinctive Mesozoic pollen grains assigned to the genus Eucommiidites. These data indicate that Eucommiidites producers (Erdtmanithecaceae) comprise an extinct clade with probable close affinities to the Gnetales.