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Habit and leaf form. Aquatic herbs. Plants more or less succulent (the branches and petioles spongy and aerenchymatous). Perennial. Leaves basal and cauline (several at the base and 1 on the flowering stem). Plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves; rhizomatous (creeping to almost erect, bears membranous bracts). Hydrophytic; rooted. Leaves emergent; alternate; spiral, or distichous; petiolate (long on the cauline leaf); sheathing. Leaf sheaths tubular. Leaves simple. Leaf blades entire; parallel-veined (numerous, or finely curvinerved); without cross-venules; of the terminal leaf is sheathed, the portion above the sheath is 2/5 to 5 times as long as the sheath. Leaves ligulate, or eligulate; without stipules. Leaf blade margins entire. Leaf anatomy. Hairs absent. Extra-floral nectaries absent. Stem anatomy. Secondary thickening absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants homostylous. Floral nectaries present. Nectar secretion from the gynoecium (via septal nectaries). Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes (raceme-like), or in spikes (spike-like), or in umbels (sub-umbel). The terminal inflorescence unit cymose, or racemose. Inflorescences terminal; flowering stem erect; inflorescence emerges from the sheath of the terminal leaf and an axillary sheathing bract; peduncle deflexed after anthesis so the inflorescence submerged in fruit; spatheate, or espatheate. Flowers pedicellate (long); bracteate; ebracteolate; small to medium-sized; regular, or somewhat irregular; when irregular, zygomorphic. The floral asymmetry involving the perianth, or involving the perianth and involving the androecium. Flowers 3 merous; pentacyclic. Perigone tube present. Free hypanthium staminal filaments adnate to the perianth tube. Perianth of ‘tepals’; 6 (in 2 whorls); 2 -whorled; isomerous; free, or joined; petaloid; without spots, or spotted; similar in the two whorls; blue and white (with a green midrib that becomes thickened). Androecial members definite in number. Androecium 6. Androecial members adnate; all equal (A), or markedly unequal (A); free of one another, or coherent (variously connate); 2 -whorled (3+3). Androecium exclusively of fertile stamens. Stamens 6; all more or less similar in shape (A), or distinctly dissimilar in shape (bearing a lateral appendage); diplostemonous; at the base of the perianth; alterniperianthial. Filaments appendiculate (A), or not appendiculate (A). Anthers basifixed; dehiscing via pores (terminal); introrse. Gynoecium 3 carpelled. The pistil 3 celled. Carpels isomerous with the perianth. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 3 locular; sessile. Gynoecium stylate. Styles 1; attenuate from the ovary; apical. Stigmas 1; 3 - lobed. Placentation axile. Ovules 20–50 per locule (many); pendulous; non-arillate; anatropous.
Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Fruit 3 celled; 20–100 seeded (many). Seeds endospermic. Endosperm not oily. Embryo well differentiated. Cotyledons 1. Embryo straight.
Etymology. From the Greek for "single" and "apart, alone"; one stamen differs from the other five.