Erwin, Diane M. .
Late Eocene pond weeds from the Bull Run Basin, NV, USA.
Hundreds of fruits and remnants of infructescences collected from the Eocene Bull Run Basin in northeastern Nevada show morphologies similar to extant Ruppiaceae (Ruppia), Potamogetonaceae (Stuckenia), and Zannichelliaceae. The Ruppia-like remains include isolated ovoid fruits, many containing embryos with a short, but well-defined cotyledonary lobe and enlarged hypocotyl. Fruits are 1.9-3.0 mm long X 1.4- 2.0 mm wide, have a slender erect style, a raised “shoulder” area adjacent to the style, a dorsal, flap-like germination valve that extends distally from a short distance above the fruit base to the shoulder, and a long, straight, slender fruit stalk, 1.0-2.1 cm long X 0.15-0.25 mm wide. Inflorescence remains are of three types: (1) slender axes with a single stipitate fruit attached laterally; (2) axes with two laterally attached stipitate fruits ventrally opposed and separated by a short distance (0.7-1.0 mm); and (3) single stipitate fruits attached laterally to opposite sides of the axis separated by lengths of 3.0-5.0 mm. As interpreted here the number of flowers is at least two per inflorescence and the carpel number is at least two. Morphologically, the fruits and slender inflorescence axes share certain features with all three families. As in Stuckenia, fruits are oblanceoloid, 2.0-3.0 mm long X 1.6- 2.5 mm wide, have a flap-like germination valve, some show a warty surface and the cotyledon of the embryos shows less than one full coil. However, unlike Stuckenia, the fruits are not sessile but stipitate, with stalks 0.8-1.35 mm long X 0.15 – 0.25 mm wide, and the style is long and slender with a peltate stigma, features more commonly found in Ruppia and Zannichelliaceae. The Bull Run fossils are presented in light of the unresolved phylogenetic relationship between the Ruppiaceae and Potamogetonaceae.
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1 - University of California, Museum of Paleontology, 1101 Valley Life Sciences Building, Berkeley, CA, 94720, USA
Bull Run Basin.
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 2:00 PM