Evolution of aquatic life-forms in Alismatidae : Phylogenetic estimation from chloroplast rbcL gene sequence data

The molecular phylogeny of Alismatidae based on analysis of chloroplast rbcL gene sequence data serves as a framework within which to evaluate the evolutionary advancement of aquatic life-forms in this group. Forty-five genera representing all currently recognized families in the subclass are included in our study. The present analysis indicates that the submersed, floating-leaved, and free-floating life-forms are all polyphyletic within the subclass Alismatidae. Three independent origins of the submersed life-form in Alismatidae with one reversal to emergent life-form are explored in this study. Two separate origins of the free-floating life-form and three separate origins of the floating-leaved life-form in the subclass are also suggested. It is possible for the free-floating life-form to have been derived directly from the submersed life-form and it could also be that the free-floating life-form has been derived from the emergent one. The emergent life-form is considered as progenitorial in the Alismatidae, giving rise to submersed, floating-leaved, and free-floating forms by adaptive radiation.