Stults, Debra , Axsmith, Brian .
Trapa fruits from the Late Tertiary of eastern North America.
THE genus Trapa (family Lythraceae) is a freshwater herb naturally occurring in Eurasia and Africa. Although extinct in North America, it occurs in the fossil record beginning in the Eocene, continues through the Pliocene, and disappears probably in association with Pleistocene climate deterioration. Inadvertently reintroduced to North America in the late 1800s, it occurs as a troublesome exotic in the northeastern United States. Trapa's tetramerous flower is inconspicuous, but the coriaceous fruit is easily recognizable due to its sharp horns derived from the calyx. Thus, fruit characteristics are commonly used for species delimitation. Complicating these determinations, however, is considerable morphological variability found within and among various populations. This has resulted in controversial analysis of systematically-significant features. Based upon available data, it appears that the most reliable fruit characters may be horn number, size, retrorse barbs on horns, incurved or recurved horns, and fruit color. Confusion over species delimitations may extend into the fossil record. Angular measurements of horns and fruit body, description of protuberances, tubercles, and possible pseudo-horns are used extensively. Reinvestigations of the flora of the Mid-Pliocene Citronelle Formation and the Late Miocene Brandywine Deposit allow for an updated description of Trapa alabamensis, based on excellent new specimens, and a description of a new, four-horned form from the Mid-Atlantic Coastal Plain. Both types are in the intermediate-sized category (25-35 mm and 34-38 mm across upper horns, respectively). The Brandywine fruits exhibit greater morphological variability than seen in the Citronelle Formation specimens. Tubercles and protuberances in the Brandywine fruits are sharper and conical, while in T.alabamensis they are softly rounded. The combined presence of these forms suggests a greater diversity of Trapa in eastern North America than was previously realized.
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1 - University of South Alabama, Department of Marine Sciences, Life Sciences Bldg 25, Mobile, Alabama, 36688, USA
2 - University of South Alabama, Biological Sciences, Life Sciences Bldg. #124, 307 University Blvd. North, Mobile, Alabama, 36688, USA
Eastern North America.
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, August 1st, 2006
Time: 10:45 AM