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(American Journal of Botany. 2006;93:724-738.)
© 2006 Botanical Society of America, Inc.

Paleobotany

Cataphylls of the Middle Triassic cycad Antarcticycas schopfii and new insights into cycad evolution1

Elizabeth J. Hermsen4, Thomas N. Taylor, Edith L. Taylor and Dennis Wm. Stevenson

2Department of Ecology and Evolutionary Biology and Natural History Museum and Biodiversity Research Center, University of Kansas, Lawrence, Kansas 66045-7534 USA; 3The New York Botanical Garden, Bronx, New York 10458 USA

ABSTRACT

Cataphylls associated with the Middle Triassic stem genus Antarcticycas are described, and their impact on understanding cycad evolution is discussed. The cataphylls of Antarcticycas are triangular in outline and flattened adaxially with lateral flanges. The outer surfaces are covered with a ramentum of filamentous hairs, the epidermis is a single cell layer thick, and the ground tissue is parenchymatous with mucilage canals and sclereids. Vascular bundles form a distinct inverted omega-shaped pattern characteristic of the Cycadales observed in petioles of extant species. The structures in Antarcticycas are interpreted as cataphylls based on overall morphology, presence of straight vascular strands in the cortex of the associated stem, and lack of fascicular cambia in the vascular bundles. Because much of the overall diversity of Cycadales is represented by fossils, integrating fossil taxa into explicit phylogenetic hypotheses is important for understanding cycad evolution. Therefore, character and minimum age mapping were performed on a phylogeny of extant and fossil taxa including Antarcticycas. The results suggest that major extant lineages of Cycadales had diverged by the Permian to Triassic and that certain synapomorphies for Cycadales had evolved by the Permian. Evidence of insect feeding on Antarcticycas suggests that associations between cycads and insects are ancient.

Key Words: Antarctica • Antarcticycas • cataphyll • character evolution • Cycadales • minimum age mapping • phylogeny • Triassic






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