Manchester, Steven R. , Handley, Bruce .
Foliage and fruits of Populus (Salicaceae) from the Middle Eocene of Colorado..
Leaves of Salicaceae are among the most common plant fossils in Middle Eocene floras of the Rocky Mountain region, yet their taxonomy has been problematic--partly because of missing data about their reproductive organs. A newly discovered twig from the Middle Eocene Parachute Creek Member of the Green River Formation in western Colorado shows leaves of Populus attached to a reproductive shoot bearing a terminal infructescence. The fruits are pedicellate, ovate, trivalved capsules 12-14 mm long and 5-6 mm wide, of the kind previously attributed to Luehea newberryana (Knowlton) MacGinitie. The leaves are alternate, with petioles of medium length (less than 1/3 the length of the lamina) and have narrowly ovate to elliptical laminae that are serrate with glandulular teeth. Venation is pinnate, with 7-10 pairs of pinnate secondary veins including a stronger basal pair that extends over the lower 1/3-1/2 of the lamina. This species is readily distinguished by both leaves and fruits from P. wilmatae Cockerell. The latter, which is also known from a twig with attached leaves and fruits, has broadly ovate laminae, long petioles (nearly equal to the length of the lamina), and smaller fruits (5-7 mm long). These observations confirm that there were at least two distinct poplars in the Green River flora, and refute the previous hypothesis of a single Green River species with markedly heteromorphic foliage. Together with leaves, fruits and flowers of Pseudosalix handleyi Boucher, Manchester and Judd, these fossils provide the earliest confirmed records of Salicaceae. Leaves from the same geologic horizon, assigned to Salix cockerellii Brown and S. longiacuminata Knowlton, are of interest as potential early records of Salix; however corresponding fruits and flowers are still unknown.
1 - University of Florida, Department of Natural History, Florida Museum of Natural History, P.O. Box 117800, Gainesville, Florida, 32611-7800, USA
2 - 40 Elderwood Dr., Pleasant Hill, California, 94523
Green River Formation.
Presentation Type: Paper
Location: Maybird (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 2:45 PM