Stockey, Ruth , Rothwell, Gar , Johnson, Kirk .
A new species of Cobbania (Araceae) from the Cretaceous (Upper Maastrichtian) of South Dakota.
A large number of new specimens of the floating aquatic aroid genus Cobbania Stockey, Rothwell et Johnson have been recovered from pond sediments in the Hell Creek Formation of Harding County, South Dakota. Specimens are preserved as compression/impressions in a greyish brown, sandy siltstone. At least 12 rosettes of whole plants with branched aquatic roots, some of which are interconnected by stolons, show the characteristic trumpet-shaped, pubescent Cobbania-type leaves with a central aerenchymatous zone. Stems of the new plant are smaller and more delicate; leaves have shorter petioles, a larger number of primary veins, and considerably wider rims than those of C. corrugata. Leaves of both species show an apical notch and collective veins in the margin with 2-3 marginal veins and a fimbrial vein in the rim. In the new specimens the leaf rim is quite narrow near the base, but expands dramatically (6-7 times the size) toward the apex. Both plants show a similar over-all venation pattern with a large number of (up to 19 in the new species) abaxial primary veins that extend from the petiole. Stolons in the Hell Creek plants are up to 1cm wide and show evidence of probable internal vascular tissues, not seen in C. corrugata. These new Cobbania fossils come from the Upper Maastrictian, near the end of the 10 million year geologic range for the genus, and reveal that these aquatic Araceae were more diverse just prior to the K/T boundary.
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1 - Oregon State University, Department of Botany and Plant Pathology, Corvallis, OR, 97331, USA
2 - DENVER MUSEUM OF NATURE & SCIENCE, 2001 COLORADO BLVD, Denver, CO, 80205-5798, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Forsyth Room/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 8:45 AM