Genetic variability in two hydrophilous species of Potamogeton, P-pectinatus and P-filiformis (Potamogetonaceae)

Genetic variability in Potamogeton pectinatus and P. filiformis was studied by means of isozymes. The overall levels of variability were similar to some other well studied hydrophilous species, and were shown to be distributed more between than within populations. This partitioning of variability was attributed to three main factors. (1) Clonal growth (as measured by the frequency of multi-enzyme phenotypes) was shown 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 likely 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 populations is mainly by seed rather than by vegetative means.