Dilcher, David .
Deep Time—Adaptive Significance of Sex.
The fossil record is necessary to reliably answer several questions regarding the evolution of angiosperms. Fossils add the unique perspective of time and totally extinct angiosperm lineages can be recognized early in their history. Key features of angiosperms lie in the nature of their reproductive organs, of their leaves, their stems and their habit. Archaefructus, an early angiosperm, demonstrates several key characters important in understanding the reproductive biology of early flowering plants from seed plant ancestors. The one unique feature of angiosperms is the closed carpel. This single character (closed carpel) definition of angiospermy is important because it is morphologically-based, preservable character that is uniquely angiosperm. The functional importance of this character in the genetics of flowering plants should not be under estimated. Sex has everything to do with angiosperm evolution. The micropyles of most seed plants contain pollination droplets that consist of fluids often rich in substances that form a biochemical barrier to the successful germination and subsequent fertilization of pollen from the same plant. Historically as the pollen and ovule producing organs were brought into proximity of each other in bisexual reproductive units, this biochemical barrier was very important in order to prevent self-fertilization. When the earliest flowering plants were living in an aquatic environment and their ovules were borne on loosely folded leaves that were susceptible to water washing away the micropylar exudate, mechanical closure of the carpel became important. The mechanical closure of the carpel was the most secure way for early flowering plants to insure that incompatible biochemical barriers could be maintained. By means of a closed carpel, flowering plants gained an additional advantage over seed plants because of the increased genetic control they could maintain over their reproductive biology.
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1 - University of Florida, Department of Botany, Florida Museum of Natural History, P.O. Box 117800, Gainesville, Florida, 32611-7800, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Wednesday, July 11th, 2007
Time: 11:30 AM