Morphometric studies of the Sphagnum cuspidatum complex in the coastal plain of the southeastern United States

Author

Allen C. Risk

Date of Award

8-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Botany

Major Professor

David K. Smith

Committee Members

Dewey Bunting, Karen Hughes, Patricia Walne

Abstract

The Sphagnum cuspidatum complex, as expressed in the Coastal Plain of the southeastern United States, comprises six named entities: S. cuspidatum Ehrh. ex Hoffm., S. fitzgeraldii Renauld & Cardot in Lesq. & James, S. mississippiense R.E.Andrus, S. torreyanum Sull., S. trinitense Müll.Hal., and S. viridum Flatberg. Sphagnum torreyanum,/em> and S. fitzgeraldii are generally regarded as distinct, but the number of taxa represented by the other names is less certain. All named taxa assignable to the complex were evaluated using 374 collections from five areas in the Coastal Plain; of these, 135 specimens were randomly selected for intensive morphometric analysis. Five morphological groups were initially recognized based on examination under a dissecting microscope: group 1, a S. cuspidatum/S. viridum species pair; group 2, a S. trinitense/S. mississippiense species pair; group 3, S. fitzgeraldii; group 4, S. torreyanum; and group 5, a single specimen interpreted as representing a hybrid between groups 1 and 3 or an undescribed taxon. Multivariate analyses, based on measurements of twenty-two morphological characters, supported the distinctiveness of all groups. Sphagnum cuspidatum/S. viridum and S. trinitense/S. mississippiense were separated most effectively by three characters: proportion of margin not entire of the proximal branch leaves, proximal branch leaf length to width ratio, and outer stem cell layer differentiation. Intensive morphometric analyses within the S. trinitense/S. mississippiense and S. cuspidatum/S. viridum species pairs failed to find support for the recognition of either S. mississippiense or S. viridum as morphologically distinct within the study area. A second component of the study was a quantitative analysis of morphological variation along temporal and moisture gradients in S. cuspidatum. This assessment of character variability indicated that marginal features of median and distal branch leaves and number of septa in stem leaves are too variable over seasonal and moisture gradients within individual populations to serve as reliable taxonomic characters for separating S. cuspidatum from S. trinitense. Proximal branch leaf margin features, length to width ratio of proximal branch leaves, and outer stem cell layer differentiation proved to be the most reliable characters to use in discriminating among specimens of this problematic species pair.