Rotala

Annual or rarely perennial herbs; stems terete or quadrangular, glabrous. Leaves opposite-decussate or verticillate, rarely alternate, +/- sessile. Flowers homomorphic or dimorphic, occasionally cleistogamous, small, usually solitary and subsessile in leaf axils, occasionally aggregated into terminal racemes or spikes, very rarely in axillary umbels; bracts foliose or scale-like, bracteoles 2, rarely absent. Calyx: tube (3)4-6-lobed; lobes often alternating with cornate appendages; nectaries often present at base of tube. Petals as many as calyx lobes or 0, sometimes unequal, entire, erose or pinnately divided. Stamens 1-6, opposite sepals, arising at various heights in calyx tube, occasionally basal and appearing free, sometimes replaced by staminodes. Ovary sessile or shortly stipitate, incompletely 2-4-locular, dissepiments interrupted above placentas; ovules small and many; style very short to long; stigma capitate or rarely bilobed. Capsule septicidally 2-4-valved. Seeds small, few or many, concave-convex, with evaginating mucilaginous hairs. x = 8 (aneuploids, polyploidy).