Abstract Detail

Paleobotanical Section

Liu, Xiaoyan [1], Manchester, Steven  [2].

Leaves, fruiting and pollen catkins of Alnus (Betulaceae) from the Middle Eocene Clarno Formation of Oregon, Western USA.

The fossil record of alders (Alnus) is well known in the Cenozoic of the Northern Hemisphere, based on numerous reports of the distinctive pollen, cone-like infructescences, staminate inflorescences, and leaves. However, our understanding of the systematic position of these fossils relative to the modern phylogeny of the genus has been limited, because most fossil species were described from the features of only one organ. More morphological characters, available from multiple organs of the same species, are needed for detailed comparative investigations. We reconstruct a new extinct species based on well preserved leaves and associated fruiting catkins, staminate catkins, and in situ pollen from early Middle Eocene lacustrine sediments of the Clarno Formation in north central Oregon, USA. Combined investigations of each organ, believed to derive from the same species, provide an opportunity for detailed comparison with other modern and fossil representatives of the genus. The leaf blades are lanceolate, elliptical, ovate to broadly ovate with acute to accuminate apex and acute to cordate base, and have a serrate margin consisting of two orders of compound teeth. Assignment to the genus Alnus is confirmed by associated distinctive woody infructescences, 0.5-1.5 cm long and 0.5-1.0 cm wide and by the associated staminate catkins containing 3 to 6-pored suboblate pollen with arci between the pores. The catkins are narrow, elongate, cylindrical, approximately 9-34 mm long, 2-2.5 mm wide, composed of approximately 41-44 helically arranged florets, each with at least 9 anthers (maybe 12) subtended by a woody bract. Pollen pore number varies from 5 (61.5%), to 4 (27.5%) to rarely 3 (1%)- and 6 (10%) within the same catkin. Characters most important for the intrageneric placement of extant species have been emphasized to assess the position of this fossil species. Based especially on features of leaf architecture and pollen pore number frequency, the Clarno fossil is readily separated from subgenus Alnobetula, and is placed with confidence in the subgenus Alnus. In particular, the fossil species appears closest to the extant North American species, A. arguta, A. oblongifolia and A. rhombifolia, in subgenus Alnus, and is less similar to the extant species of Asia and Europe. Therefore, the Clarno fossil Alnus provides important biogeograhic evidence favoring its position as an endemic North American lineage.

1 - Sun Yat-sen University, School of Life Sciences, No. 135, Xingang Xi Road, Guangzhou, Guangdong, 510275, China
2 - University of Florida, Florida Museum of Natural History, PO Box 117800, Gainesville, FL, 32611, USA

Keywords:
Alnus
Betulaceae
Middle Eocene
Biogeographic
Oregon.

Presentation Type: Oral Paper:Papers for Sections
Session: 8
Location: Whitewater/Grove
Date: Monday, July 28th, 2014
Time: 2:00 PM
Number: 8017
Abstract ID:427
Candidate for Awards:Isabel Cookson Award