Phylogenetic studies in Callitriche: implications for interpretation of ecological, karyological and pollination system evolution

Species of Callitriche (Callitrichaceae) exhibit considerable diversity in chromosome number (n = 3-20), ecology (submersed, amphibious, semiamphibiou s, terrestrial) and pollination systems (anemophily, hypohydrophily). Calli triche is the only genus of angiosperms in which both aerial pollination an d hypohydrophily have been documented. Phylogenetic analyses were conducted using morphologic and rbcL sequence characters for 20 taxa that represent the range of chromosome number, ecological and pollination system diversity in the genus. Parsimony analyses reveal 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 evolv ed once. Although internal geitonogamy (a unique self-fertilization system known only in Callitriche) occurs in at least seven species in the genus, t he analyses reveal that it likely evolved only once. (C) 2000 Elsevier Scie nce B.V. All rights reserved.