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New Diversity among Chlamydospermous Seeds from the Early Cretaceous of Portugal and North America

Else Marie Friis, Kaj Raunsgaard Pedersen and Peter R. Crane
International Journal of Plant Sciences
Vol. 174, No. 3, Special Issue: Conceptual Advances in Fossil Plant Biology Edited by Gar Rothwell and Ruth Stockey (March/April 2013), pp. 530-558
DOI: 10.1086/668250
Stable URL: http://www.jstor.org/stable/10.1086/668250
Page Count: 29
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New Diversity among Chlamydospermous Seeds from the Early Cretaceous of Portugal and North America
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Abstract

Five species of seeds are described in four new genera that are broadly similar to seeds of the Bennettitales, Erdtmanithecales, and Gnetales (Tomcatia taylorii, Tomcatia sp., Cattomia trapezoides, Acanthocatia virginiensis, Quadrispermum parvum). The material is based on numerous charcoalified and lignitic specimens recovered from Early Cretaceous mesofossil floras in Portugal (Arazede, Buarcos, Catefica, Famalicão, Torres Vedras, Vale de Agua) and eastern North America (Puddledock). The seeds all have a prominent seed envelope that encloses a thin integument and the lower part of the long, slender micropylar tube. Seeds of all four genera are distinguished from previously described seeds of this kind in having a strongly four-angled seed envelope with distinct transverse ridges that create a rugulate seed surface. The seed envelope is composed of sclerenchyma cells toward the inside and an outer zone of nonlignified cells toward the outside. The outer zone is often composed of distinctive and prominent elongated cells that are very similar in position and form to the tubular cells reported in seeds of Bennettitales. In Cattomia the tubular cells are especially well-developed at the apex and base of the seeds, as well as along the angles of the seed envelope. In Tomcatia and Acanthocatia they form pronounced apical projections and are also present over the angles of the seed envelope and at the base. In Quadrispermum, where the seeds are borne in the axils of opposite bracts, the tubular cells are less well developed but are nevertheless present at the base of the seed. It is unknown how the seeds of the other taxa were borne, but in Cattomia the strongly developed sheet of tubular cells at the base of the seeds suggests that they were not borne in the same way as seeds of Quadrispermum. The distinctive organization of the seeds seen in Tomcatia, Cattomia, Acanthocatia, and Quadrispermum links them to previously described seeds of Erdtmanithecales and Gnetales. Similarities in seed organization, combined with the presence of the tubular cells, as seen especially clearly in Cattomia, provide further evidence of a close relationship of some of the dispersed seeds to Bennettitales.

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