Callitrichaceae
Fls minute, unisexual, axillary, solitary, or ♂ and ♀ paired; ♂ reduced to 1 stamen with long slender filament; ♀ a 4-lobed ovary, 4-celled by secondary septa; styles 2, elongate, papillose; ovules solitary in each cell, pend. Fr. 4-lobed; lobes ± keeled or winged, separating into 4 compartments at maturity. Annual to perennial glab. herbs, us. aquatic or subaquatic, with very slender stems; lvs opp., us. entire, exstipulate. A single almost cosmopolitan genus with some 20 spp.
