Taylor, Wilson A. , Gensel, Patricia G. , Wellman, Charles H. .
Spore wall ultrastructure of the Devonian form genus Emphanisporites.
Among dispersed Silurian-Devonian spore genera whose taxonomic affinities are obscure, none are more distinctive or widespread than Emphanisporites. Members of this form genus possess radiating sculptural patterns on their proximal surfaces. In an attempt to determine the parent plant(s) of this spore type, we examined several species using transmission electron microscopy (TEM) of numerous serial sections. One specimen of E. rotatus has evenly thickened, bi-layered, faintly laminated walls, a pointed sutural emergence, a well developed equatorial thickening, and a prominent interradial multilamellated zone at the innermost extent of the main spore wall (exospore). A second specimen of this taxon has a thinner, less evenly thickened exospore, with no obvious layering, a poorly developed equatorial thickening, no pointed sutural emergence, and appears to lack interradial multilamellated zones. Two specimens of E. annulatus are less variable, but they also lack interradial multilamellated zones. One specimen of E. schultzii has a distal exospore composed of prominent, short, discontinuous laminae, and a proximal exospore with a radiating ultrastructure. This specimen also appears to lack interradial multilamellated zones. This degree of ultrastructural variability is unexpected, and suggests that very different plant groups may have produced these spores, seemingly converging on a common structural theme that is apparent when viewing under light microscopy. The only specimen whose affinity seems assured is that possessing the interradial multilamellated zones, which are known to be present only in lycophyte spores. It is possible that some of the differences seen may be attributable to natural variation, developmental stage, or preservational vagaries, but we discount these as the main agents. Such widespread appearances of generalized morphological types occur throughout the dispersed spore/pollen record (e.g., permanent tetrads, dyads, taeniate pollen, triprojectate pollen) and may record adaptive radiations, convergence due to common (as yet unrecognized) function, and/or some other pathway of evolutionary/informational transmission.
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1 - University of Wisconsin-Eau Claire, Department of Biology, Eau Claire, WI, 54701
2 - University of North Carolina, Department of Biology, Cb#3280, Chapel Hill, North Carolina, 27599-3280, USA
3 - University of Sheffield, Animal and Plant Sciences, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Superior A/Cliff Lodge - Level C
Date: Monday, July 27th, 2009
Time: 2:00 PM