Symmetry and Development of Pistillate Vallisneria Americana (Hydrocharitaceae)

Pistillate Vallisneria americana produces upright vegetative axes and prostrate stolons and develops in a manner fundamentally similar to that of Limnobium spongia (Hydrocharitaceae) and certain other taxa of Alismatidae. The cauline portions of pistillate V. americana branch solely by the bifurcation of apical meristems, and their mode of branching offers clues concerning the nature of the plant body. The upright axes are interpreted to have sympodial growth, whereas at least certain stolons appear to be entirely monopodial. The upright axes are either typical vegetative axes or turions; and of these, only turions appear to survive the winter in at least one locality. Pistillate V. americana produces intravaginal squamules (multi‐seriate trichomes) although they appear reduced in number relative to those in certain other hydrocharitaceous and alismatid taxa. Vallisneria americana exhibits a notable degree of mirror image symmetry which differs somewhat from that of Limnobium spongia.