Pontederiaceae

Abstract

Submerged, floating or emergent, freshwater annuals or perennials. Stems of two kinds, vegetative and flowering; vegetative stems indeterminate, with many leaves, with or without sympodial rhizomes or stolons; flowering stems determinate, leafless, bearing a spathe and a terminal inflorescence. Leaves distichous or spiro-distichous, “pseudo-whorled” in Hydrothrix (see below), often scalelike on rhizomes and stolons, cauline or basal, usually sheathed at the base; stipules axillary or median, either large and enveloping the stem, forming an ochrea, or reduced to a small sheath or ligule or absent; juvenile leaves simple and linear; adult leaves either simple and linear or clearly differentiated into petiole and blade; petioles of variable length, sometimes inflated; blades simple, submerged, floating or emergent, glabrous, linear to orbicular or sagittate, with entire margin, venation acrodromous. Inflorescence terminal, a panicle, umbel-like, a spike, or flowers paired or solitary, subtended by 2 opposed spathes (bracts), one often leaflike, the other sheathing or both leaflike or sheathing; peduncles glabrous or glandular pubescent. Flowers bisexual, zygomorphic or almost actinomorphic, some triheterostylous. Tepals usually 6, sometimes reduced to 4 or 3, equal or unequal, all petaloid, usually withering early, free almost to the base or united basally into a tube, white, blue, pink mottled with yellow or yellow. Stamens all alike or dimorphic, 6, 4, 3 or 1; filaments inserted on the perianth, similar or dissimilar, elongate or swollen, straight or twisted, glabrous or hairy; the hairs linear and smooth, glandular, or moniliform; anthers similar or dissimilar, 2-thecate, basifixed or auriculate and thus appearing dorsifixed, dehiscing introrsely by longitudinal slits or through apical pores, remaining straight or coiling, yellow, blue, brown or black. Gynoecium of 3 united carpels; ovary superior, 3-locular, sometimes only 1 locule fertile; placentation axile or appearing parietal with intrusive placentas, ovules anatropous, crassinucellar, bitegmic, solitary or numerous; style single, simple and elongate, glabrous or hairy; stigma relatively small, entire or 3-lobed, Dry. Well-developed septal nectaries present in Eichhornia and Pontederia. Fruit a capsule or a 1-seeded nutlet enclosed in a specialized perianth base (anthocarp). Seeds numerous or solitary, ovoid, usually with longitudinal ribs; endosperm starchy; embryo central, cylindrical, linear; cotyledon terminal; plumule lateral.