DNA-SEQUENCE VARIATION IN THE RIBOSOMAL INTERNAL TRANSCRIBED SPACER REGION OF FRESH-WATER CLADOPHORA SPECIES (CHLOROPHYTA)

Freshwater species of Cladophora (Chlorophyta) are globally distribute d and occupy an unusually wide range of ecological habitats. Delineati ng species is difficult because most easily observed morphological tra its are highly variable and because sexual reproduction has not been c learly documented. Synthesizing ecological data on freshwater Cladopho ra species is problematic because it is unclear whether freshwater Cla dophora species comprise many genetically distinct species or a few ec ologically and morphologically variable and / or plastic species. We d etermined nucleotide sequences of the internal transcribed spacer (ITS ) region of the nuclear ribosomal cistron of freshwater Cladophora spe cies from a wide range of habitats and geographic locations. We compar ed these sequences to those derived from culture collections of C. fra cta and C. glomerata, the two most commonly reported freshwater Cladop hora species. Cladophora fracta and C. glomerata had very similar ITS sequences (95.3%). All other sequences were identical to those from th e C. fracta or C. glomerata culture collections with the exception of one California sample that was similar to both C. fracta (95.6%) and C . glomerata (92.4%). ITS genotypes did not correlate with morphology o r geography. This analysis shows that common freshwater Cladophora spe cies comprise very few (possibly one) ecologically and morphologically variable species.