Callitriche

Callitriche is a genus of largely aquatic plants known as water-starwort. Previously, it was the only genus in the family Callitrichaceae. However, according to the APG II system this family is now included in the Plantaginaceae (plantain family). The family name Callitrichaceae retains its status as "nomen conservandum" (name to be retained).
Phylogeny and evolution.
The first molecular phylogeny of the aquatic genus of 50 species discerned three clades: Clade A (three species, widespread); Clade C (10 species, New World); Clade D (six species, Europe). The parsimony analyses revealed that aneuploid reduction (n=5 to 4) and polyploidy (n=5 to 10) have evolved at least twice in the genus, whereas the obligately submersed growth habit and hypohydrophily have evolved once.