Oospore variation in Nitella gracilis and Nitella mucronata (Charales,Charophyceae) from Poland

The determination of the members of Charales (Charophyceae) is not easy. The main reason of this is a wide range of variation in vegetative characters within most of the species. Many features such as the extent of branchlet cortication, the degree of incrustation, length and number of bract cells, spine cells, stipulodes, diameter of the main axis and oospore size and color do not have universal taxonomic significance. In similar, many Nitella species characters such as: general habitus, branchlets and presence of the top segment (mucro), are helpful in determination, however they are often not developed. In this case, the features of oospore wall ornamentation revealed by light and scanning microscopy can be important taxonomic characters of the Charales. The present study shows interspecific variations of the oospore in two Nitella species from Poland which can be helpful in correct determination of both species. Some of the oospore features like number of striae and fossa width can not be used, as they appeared statistically unimportant, and cannot be used in distinguishing between both species. The presented results are the first detailed report of oospore wall ornamentation pattern from Poland for the species studied. Oospore features are presented in detail on the background of some additional tips and among them particularly: length and width of the oospore, ISI idex, width of fossa, width of striae and number of striae.