PROBLEMS RELATING TO SPECIES SAMPLING IN PHYLOGENETIC STUDIES - AN EXAMPLE OF NON-MONOPHYLY IN CLADOPHOROPSIS AND STRUVEA (SIPHONOCLADALES,CHLOROPHYTA)

Nucleotide sequences from the nuclear rDNA internal transcribed spacer s (ITS1 and ITS2) and seven morphological characters were compared amo ng 10 isolates of siphoncladalean algae representing six species in Bo odlea, Chamaedoris, Cladophoropsis and Struvea. Parsimony analysis of both datasets revealed that Struvea is not monophyletic, Struvea elega ns Borgesen being more closely related to Chamaedoris peniculum (Ellis et Solander) Kuntze and Struvea anastomosans (Harvey) Piccone et Grun ow being more closely related to Cladophoropsis membranacea (Hofman Ba ng ex C. Agardh) Borgesen. Parsimony analysis of the ITS data further indicates that Cladophoropsis is not monophyletic and that Cladophorop sis and Boodlea may be paraphyletic. The influences of life history st rategies, overlapping gene pools and the possibility of introgression are discussed. Finally, the point is made that although the results he lp to clarify phylogenetic relationships among species within these ge nera, they also illustrate the hazard of a priori assumptions about ge neric monophyly in which a single species (often the most commonly rec ognized one) is used to represent that genus in a biogeographic and/or phylogenetic study.