Plants aquatic, upright, often dying back to rhizome in winter [dry season], 1--3.5 m. Rhizome not evidently enlarged or specialized for starch storage. Stems unbranched below inflorescence; leaves all basal or rarely with single cauline leaf borne above elongate (0.7--2.5 m) internode. Leaves homotropic; sheath not auriculate, spongy, containing prominent air spaces; blade plain green, ovate to elliptic. Inflorescences branched, branches short and upright to elongate and arching; rachis internodes conspicuously zigzagged; bracts deciduous, both bracts and prophylls falling with flower if fruit not set, leaving proximal portion of rachis bare, each bract subtending 1 flower pair, herbaceous to leathery; prophylls not evidently keeled, membranous; secondary bracts absent; bracteoles absent. Flowers self-fertilizing [outcrossing], pale to dark purple (corolla and staminodes); sepals persistent in fruit, 0.5--3 mm, membranous; corolla tube 1--6 mm, corolla lobes subequal to strongly unequal; outer staminode 1, petal-like, showy; callose staminode mainly fleshy, narrow apical rim petal-like; cucullate staminode with 2 appendages, subterminal, finger-like; stylar movement helical when tripped; styles with 1 appendage, elongate, straplike. Fruits capsules, 1-seeded, nearly globose to ellipsoid, pericarp thin, indehiscent. Seeds dark brown, nearly globose or ellipsoid, smooth; perisperm canals 2, curved; aril reduced. x = 6.
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Rhizomatous caulescent perennial herbs; leaves 2-ranked, both basal and cauline; inflorescence laxly paniculate, the rachis closely and sharply zig-zag; bracts more or less foliaceous, caducous immediately after anthesis; sepals 3, free and equal; corolla with a very short tube, the lobes 3, equal, hyaline; fertile stamen 1, somewhat petaloid; staminodia 3, the outer solitary, conspicuously petalaceous; ovary inferior, 1-celled; fruit nut-like and indehiscent, 1-seeded.
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