GENETIC-VARIABILITY IN 2 HYDROPHILOUS SPECIES OF POTAMOGETON, POTAMOGETON-PECTINATUS AND POTAMOGETON-FILIFORMIS (POTAMOGETONACEAE)

Genetic variability in Potamogeton pectinatus and P. filiformis was st udied by means of isozymes. The overall levels of variability were sim ilar to some other well studied hydrophilous species, and were shown t o be distributed more between than within populations. This partitioni ng of variability was attributed to three main factors. (1) Clonal gro wth (as measured by the frequency of multi-enzyme phenotypes) was show n to be a major factor in both species, although more important in P. pectinatus. (2) Low levels of sexual reproduction were shown to be a l ikely contributor to the partitioning of variability in P. pectinatus; such reproduction is probably limited by seedling recruitment rather than by infrequent flowering. (3) Geographical isolation was indicated as a factor regulating gene flow at distances of more than about 1000 km in both species, with the data suggesting that dispersal between p opulations is mainly by seed rather than by vegetative means.