Potamogetonaceae Bercht. & J.Presl
Infl. a bractless, ∞-fld spike; peduncle axillary and sheathed at its base. Fl. small, green, bisexual, actinomorphic. Per. represented by 4 free, valvate, concave segs adnate to the connectives of 4 stamens and alternating with 4 carpels. Anthers 2-celled, apparently sessile, extrorse. Carpels sessile, free, superior; stigma sessile or nearly so; ovule solitary, strongly curved. Achenes drupe-like when fresh; endocarp stony, splitting by separation of vertically oriented operculum on outer face. Aquatic herbs of brackish or fresh water or of marshy places. Lvs simple, us. alt., often dimorphic, submerged ones narrower and more delicate than floating ones. Stipule a delicate membrane, either free throughout or adnate to lf-base except for a free ligule, in each case either closed forming a tube round stem or open with margins overlapping on side of stem remote from lf. Two genera, one confined to N. Hemisphere.
Sattler (Amer. J. Bot. 52, 1965, 35–41) discusses various interpretations of the fl. and the per., and records developmental studies showing that the per.-segs are not outgrowths of the stamen connectives.
