Stults, Debra , Axsmith, Brian , Liu, (Christopher) Yusheng .
Haploxylon pines from the Mid-Pliocene Citronelle Formation.
Plant fossils from the Citronelle Formation provide a rare window into the Mid-Pliocene flora and climate of the northeastern Gulf of Mexico Coastal Plain. Many of the taxa recovered to date inhabit the region today. However, analysis of Pinus pollen grains and fascicles indicate that the dominant pines were members of the subgenus Haploxylon (i.e., "white pines"). The fascicles have a small, bulbous base lacking a sheath, and bear four or five long, slender needles. These features are typical of white pines. Although macrofossils are rare, most of the dispersed Pinus pollen grains have sacci continuous with the corpus and verrucae on the cappula, which are characteristics of Haploxylon pines. This is remarkable, as the Gulf Coastal Plain today is devoid of white pines, and is instead considered a center of diversity for Diploxylon pines of subsection Australes. Today, P. strobus is the only white pine in the eastern US, and its historical biogeographic relationships to other North American forms are unclear. For example, its close relative, P.chiapensis, is present in northeastern Mexico and Central America occupying elevations varying from 500 to 2250 m in regions with 1500 to 3000 mm annual precipitation. The current disjunction between P. strobus and P. chiapensis is 2000 km and includes an arid barrier to dispersal. P. chiapensis is also associated with several other species showing a similar biogeographic pattern. The fossils described here indicate that white pines were more widespread in North America in the recent geological past than previously thought, and imply possibly connections between disjunct species that would not be suspected if only current species' ranges and ecological tolerances were considered.
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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
3 - East Tennessee State University, Biological Sciences, PO Box 70703, Johnson City, TN, 37614-1700, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, July 30th, 2008
Time: 1:30 PM