Zygosporevorming bij Netrium digitus met indicatie van interne taxonomische differentiatie

Of Netrium digitus (Ralfs) Itzigs. et Rothe, two different types of zygospore configurations have been described. The first one, described by Grönblad (1920) from Finland, shows a globose, smooth-walled zygospore in between highly conical, empty gametangial cells (our fig. 1). In the second one, depicted by Homfeld (1929) from N.W. Germany, the gametangial cells are about elliptic with on one side a distinct median indentation (our fig. 2). Homfeld (l.c.) attributed his find to Netrium digitus var. lamellosum (Bréb.) Grönblad. Since then, zygospores of that type were linked to the above variety whether or not the vegetative cells belonging to it showed the median constriction considered to be characteristic of that taxon. Ohtani (1990) from experimental studies concluded a median cell constriction to be taxonomically irrelevant. Next to Netrium digitus var. digitus characterized by the conical gametangial cells, within the Netrium digitus complex he described a number of new species, all of them marked by the Homfeld-type of gametangial cells. That latter type was recently encountered in Belgian Flanders (our fig. 4 and 9) fitting Netrium lanceolatum as described by Ohtani (l.c.).