Taylor, Wilson A. , Gensel, Patricia G. , Wellman, Charles H. .
Sporoderm ultrastructure in the Devonian lycopsid Leclercqia.
An analysis of sporoderm ultrastructure of in situ spores from Leclercqia complexa and L. andrewsii was undertaken as part of a comprehensive assessment of spore morphology/structure throughout the lycopsids and their likely progenitors, the zosterophylls. Falling within the range of morphology circumscribed by the dispersed spore taxon Acinosporites lindlarensis Riegel, spores of both species; average approximately 75μm; have dense biform sculptural elements on the distal surface, and smaller and less dense biform elements on the proximal surface; and have a detectable change in sculpture type near the equator. Laesurae are sometimes folded and emergent, and sometimes in a shallow groove. When examined with TEM, spores of both species show two principal layers. The inner is laminated, thicker proximally, forms the proximal suture, and is interpreted as the exospore. The outer is thicker distally, forms the sculptural elements, and is interpreted as a paraexospore. The outer surface of the exospore is covered by small structural units that differ slightly on the proximal and distal surfaces. Proximally, these units are densely distributed and shaped like radially aligned columns or spines. Distally the exospore surface has similarly shaped units to the proximal surface, but less densely distributed. These distal elements are connected to a more clearly developed basal layer that underlies the large distal sculptural elements. Suture ultrastructure is variable along the length of the laesurae, ranging from a simple fold with no significant exospore thinning, to a more elaborate fold in which the exospore thins at the peak. This complex exospore structure is similar to that seen in Cirratriradites annulatus spores recovered from the Pennsylvanian lycopsid Selaginellites crassicinctus. Microspores of several extant species of Selaginella and Isoetes display similar complexity, including the presence of a paraexospore.
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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 Sections
Date: Monday, July 28th, 2008
Time: 3:00 PM