• Jane C. Marks,

    1. Department of Integrative Biology, University of California, Berkeley, California 94720
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      Author for reprint requests at U.S.A.I.D., G/ENV/ENR, SA18, Rm 509, Washington, D.C. 20523-1812.

  • Michael P. Cummings

    1. Department of Integrative Biology, University of California, Berkeley, California 94720
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      Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124.

  • 1

    Received 6 September 1995. Accepted 19 August 1996.

  • We thank Tom Bruns for the generous use of his laboratory and for his helpful comments and insights, Mary Power, Craig Osenberg, and Bruce Hungate for their intellectual contributions, Tim Tsaro for technical support, and John Smiley for his Big Creek hospitality. We thank Margaret Joska for the South Africa sample. The alpha test version of PHYLIP 4.0 was kindly provided by J. Felsenstein, J.C.M. was supported by a U.C. regents fellowship, an Office of Naval Research Fellowship, a U.C. Natural Reserve System Mildred Mathias Grant, a Hardmann Foundation Grant, and Phycological Society of America Grants in Aid and Croasdale awards. The research leading to this report was supported by the University of California, Water Resources Center, as part of Water Resources Center Project UCAL-WRC-W-825, and by NSF grants BSR-9106881 and DEB-9319924 to Mary Power. M.P.C. was suported by an NIH gram to Montgomery Slatkin.


Freshwater species of Cladophora (Chlorophyta) are globally distributed and occupy an unusually wide range of ecological habitats. Delineating species is difficult because most easily observed morphological traits are highly variable and because sexual reproduction has not been clearly documented. Synthesizing ecological data on freshwater Cladophora species is problematic because it is unclear whether freshwater Cladophora species comprise many genetically distinct species or a few ecologically and morphologically variable and/or plastic species. We determined nucleotide sequences of the internal transcribed spacer (ITS) region of the nuclear ribosomal cistron of freshwater Cladophora species from a wide range of habitats and geographic locations. We compared these sequences to those derived from culture collections of C. fracta and C. glomerata, the two most commonly reported freshwater Cladophora species. Cladophora fracta and C. glomerata had very similar ITS sequences (95.3%). All other sequences were identical to those from the 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 or geography. This analysis shows that common freshwater Cladophora species comprise very few (possibly one) ecologically and morphologically variable species.