Attempted Hybridization Between Monoecious and Dioecious Clones of Chara

The suggestion has been made that within the genus Chara the condition of monoecism or dioecism is of limited taxonomic significance, and that this character reflects only minor genetic variation, rarely sufficient to prevent hybridization between two otherwise similar clones. Objections have been raised to this suggestion. The present investigation was undertaken to determine whether the eggs of dioecious C. rusbyana could be fertilized by sperm from monoecious C sejuncta , monecious C. zeylanica , or dioecious C. kenoyeri ; and in turn whether the eggs of C. sejuncta and C. zeylanica could be fertilized by sperm from C. rusbyana. On the basis of 83 crosses involving 28 clones of the four taxa, we conclude that C. rusbyana is genetically isolated from the other three.