HABIT : evergreen aquatic herbs, stem thick, hypogeal, upright, annulate, terete, brown outside, white inside, usually unbranched, rarely branched, roots thick, somewhat spongy. LEAVES : 6-12, dark green in all parts except whitish hypogeal lower part of petiole. PETIOLE : sheath long, fleshy. BLADE : linear, somewhat bullate, acute to cuspidate, cuneate at base, midrib pronounced; primary lateral veins pinnate, numerous, 35-60 per side, joined into submarginal collective vein, marginal vein also present, higher order venation reticulate. INFLORESCENCE : solitary, held above water level. PEDUNCLE : much longer than petiole. SPATHE : erect, constricted between tube and blade, tube convolute, persistent, blade long-acuminate, never reflexed, marcescent after anthesis and later deciduous, bronze-green outside, cream-coloured inside. SPADIX : shorter than spathe, subcylindric, basal half of female zone adnate to spathe, separated from male by zone of sterile flowers, male zone fertile to apex. FLOWERS : unisexual, perigone absent. MALE FLOWER : 3-4-androus, stamens connate into synandrium, synandrium truncate, irregularly 4-6-angled, thecae 6-8, lateral, elongate, dehiscing by apical pore. POLLEN : ellipsoid, medium-sized (mean 44 µm.), exine foveolate-reticulate. FEMALE FLOWER : ovary cylindric, 1-locular, ovules (1-)2-3(-4), anatropous, funicle distinct, placenta basal, stylar region broader than ovary, stigma discoid-hemispheric. BERRY : subovoid, tightly packed, dull maroon-green apically, stigma remains persistent, pericarp fleshy, usually 1-seeded, sometimes 2-seeded. SEED : large, obovoid, compressed when paired, testa smooth, embryo globular, large, green, plumule well-developed, raphe prominent, endosperm nearly absent.