TAYLOR, WILSON. Department of Biology, University of Wisconsin-Eau Claire, Eau Claire, WI 54701. - Ultrastructural variability of lower Paleozoic trilete spores.
Continuing investigations of early land plant spore wall
ultrastructure are beginning to reveal a considerable degree of
diversity, despite a limited number of taxa defined at the level of
the light microscope. Previous analyses of in situ cryptopsore monads
showed several ultrastructural types within a single taxon,
Laevolancis divellomedium. A similar situation seems to exist
with some dispersed trilete spores (e.g., Ambitisporites).
Variable characteristics of these trilete spores include the relative
thickness of the proximal and distal walls, the nature of the presumed
proximal suture, and the number of sublayers comprising the wall.
Thus far, no lamellae have been identified in any dispersed trilete
spore. These trilete spores are from geographically diverse locations
(eastern US, eastern Canada, central US, eastern Europe and Saudi
Arabia), range in age from Middle Ordovician to Upper Silurian, and
have different degrees of thermal maturity. Therefore, much
additional work will need to be done to determine the extent to which
these factors are contributing to the apparent structural diversity.
Although broad categories of ultrastructural types will no doubt
ultimately become apparent, as yet, many dispersed spore taxa seem to
represent heterogeneous assemblages.
Key words: cryptospores, Ordovician, palynology, Silurian, spores, trilete