DISTRIBUTION AND SYSTEMATICS OF FRESH-WATER HILDENBRANDIA (RHODOPHYTA, HILDENBRANIALES) IN NORTH-AMERICA

Multivariate and image analyses of various cell and thallus features w ere used to determine the number of well-delineated infrageneric taxa of freshwater Hildenbrandia in North America. Thirty-four populations were collected from Belize, Costa Rica, seven Caribbean islands and so uth-central Texas. Stream segments sampled tended to be high in water temperature (xBAR = 21-degrees-C), pH (xBAR = 7.9) and specific conduc tance (xBAR = 223 muS cm-1). Four groupings of populations and type sp ecimens were differentiated with cluster and principal components anal yses. The type of Hildenbrandia angolensis was grouped with the North American populations whereas the types of H. rivularis and H. rubra we re unassociated. The type of H. rivularis had significantly larger cel l size while the type of H. rubra had significantly smaller cell size than the populations or other types. Since no other characteristics al lowed taxonomic discrimination, we consider the freshwater populations of North America to represent a single taxon, Hildenbrandia angolensi s, which is distinguished from the marine H. rubra only by the absence of tetrasporangia and the presence of gemmae.