Robust, perennial, erect, fleshy, rooted, freshwater aquatic herbs with irritant sap, forming large colonies; true stem an underground rhizome. Leaves several, forming rosulate crown at apex of massive banana-like pseudostem formed by imbricate leaf-sheaths; petiole massive, succose; sheath very broad, extending almost to non-pulvinate apex; blade sagittate; main side veins evanescent before reaching margins, finer venation striate, parallel to primary lateral veins. Inflorescences erect, appearing with leaves, much shorter than leaves, pendent in fruit. Spathe constricted centrally, basal part convolute, forming persistent fleshy tube, apical part expanded, erect, acuminate, eventually deciduous. Spadix differentiated into 4 zones: basal pistillate part with cuneiform staminodes scattered between pistils; lower sterile part with compressed prismatic sterile flowers (synandrodia); central part fertile, staminate; terminal sterile appendix bearing free to irregularly connate sterile flowers. Flowers unisexual, lacking perigon, densely congested. Staminate flower a fleshy, prismatic, truncate synandrium of 4–8 connate stamens; anthers lateral, dehiscing by oblique apical slits. Pistil shortly ovoid; ovary unilocular, with 1–2 orthotropous basal ovules; stigma subsessile, 3–6-lobed. Berries 1–2-seeded, borne in large subellipsoid infructescence surrounded by persistent spathe-tube. Seeds large, globose, lacking endosperm.
HABIT : evergreen, robust to gigantic herbs (to 4m), rhizome thick, subterranean, spreading, terminal shoot forming massive banana-like pseudostem formed by the lower part of petiole sheaths. LEAVES : several in terminal crown. PETIOLE : very long, free apical part relatively short, sheath extending for most of petiole length. BLADE : very large, subtriangular to sagittate, acute; basal ribs well-developed, primary lateral veins pinnate, forming submarginal collective vein very near to margin, 3-4 marginal veins also present, secondary lateral and higher order venation densely parallel-pinnate. INFLORESCENCE : 1-2 in each floral sympodium. PEDUNCLE : erect, bent downwards in fruit. SPATHE : erect, constricted between tube and blade, tube convolute, oblong-ellipsoid, green, persistent, blade longer than tube, narrowly boat-shaped, acuminate, gaping at anthesis, cream-coloured, marcescent, later deciduous. SPADIX : shorter than spathe, sessile, free, differentiated into 4 zones, basal female zone with cuneiform staminodes scattered between gynoecia, separated from male zone by narrower zone of sterile male flowers, male zone thicker, subcylindric-conoid, terminal zone composed of sterile male flowers. FLOWERS : unisexual, perigone absent. MALE FLOWER : 4-6-androus, stamens connate, synandrium truncate, connective very broad, thecae lateral, sessile, dehiscing by short longitudinal slit. POLLEN : inaperturate, ellipsoid, medium-sized (mean 45 µm.), exine subverrucate or obscurely foveolate or punctate. LOWER STERILE MALE FLOWERS : synandrodium truncate, subhexagonal becoming narrowly rhomboid to trapezoid towards male zone. UPPER STERILE MALE FLOWERS : composed of 3-6 obpyramidal, truncate staminodes, irregularly connate or merely crowded together. FEMALE FLOWER : gynoecia surrounded by irregularly scattered, obpyramidal, truncate staminodes, ovary shortly ovoid to globose, 1-locular, ovule 1(-2), orthotropous, funicle thick, short, placenta basal, style very shortly attenuate, stigma rather broad, shallowly 3-6-lobed. BERRY : borne in subcylindric, pendent infructescence enclosed in persistent spathe tube, berries very large, compressed-obovoid to -globose, bright yellow, pericarp fleshy. SEED : large, compressed-obovoid, testa thin, ± smooth, embryo very large, plumule exceptionally well-developed with several leaf primordia, endosperm absent.
Giant helophytes (to 4 m) forming extensive colonies with massive banana-like pseudostem formed by petiole sheaths; leaf blade sagittate, submarginal collective vein present together with 3-4 distinct marginal veins, fine venation parallel-pinnate; peduncle bent downwards in fruit; flowers unisexual, perigone absent; male flower a truncate synandrium; berries large, yellow. Differs from Peltandra in massive pseudostem of petiole sheaths, longer sterile zone between male and female zones and Madagascan range (also naturalized in Pemba, Zanzibar and Mascarene Islands).