Leslie, Andrew .
Interpreting the Function of Saccate Pollen in Fossil Conifers and Other Seed Plants.
Saccate pollen is present in many ancient gymnosperm taxa and in two families of extant conifers - the Pinaceae and Podocarpaceae. Sacci are not found on the spores of wind-dispersed pteridophytes, the pollen of anemophilous angiosperms, or the pollen of many anemophilous gymnosperms, suggesting sacci do not primarily function as aids in wind dispersal of pollen or spores. In living gymnosperms, saccate pollen is consistently found in taxa with erect ovulate cones at the time of pollination, inverted ovules, and pollination droplets. Sacci primarily function as floats which move pollen grains through the pollination droplet and concentrate them in the micropyle of the inverted ovule. The morphology and anatomy of sacci are crucial to the proper operation of this specialized gymnosperm pollination mechanism. In order to investigate the possibility that this mechanism operated in ancient conifers, a multivariate analysis of discrete pollen characters was performed on data from in situ grains of walchian, voltzialean, and extant conifer taxa, as well as several non-conifer gymnosperm groups for comparison. Preliminary results indicate that the morphology and anatomy of ancient conifer taxa is significantly different from modern saccate pollen. Fully modern saccus morphology and anatomy does not appear until relatively late in conifer evolutionary history. However, essentially modern saccate pollen morphology appears as early as the Upper Carboniferous in some non-coniferous gymnosperms, such as Callistophyton. These results suggest that sacci may have functioned in their modern capacity by the Upper Carboniferous in some gymnosperm groups, although the exact functional role of sacci in ancient conifer taxa is more difficult to assess. This study also suggests modern saccus morphology may have independently evolved several times in gymnosperms.
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1 - University of Chicago, Department of Geophysical Sciences, 5734 S. Ellis Avenue, Chicago, Illinois, 60637, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 8:30 AM