Morphological and cytogenetic characteristics of intergroup hybrids between closely related mating groups of the Closterium ehrenbergii species complex (Desmidiales, Chlorophyta)

Five F₁ hybrid strains were established from rare survivors in intergroup crosses between three closely related mating groups (A, B and H) of the Closterium ehrenbergii Meneghini ex Ralfs species complex. Cell sizes of these five strains studied under our standard culture conditions were compared to those of their parental stains and also to the total range of cell-size variation in each mating group. All five F₁ strains were larger in mean cell width than their parental strains. In cell length, three of them were larger than, one was the same as, and the other was intermediate between their parental strains. Their cell sizes were always larger than the range of their respective smaller parental mating group and three of them were larger than the range of their respective larger parental mating group.