Alismataceae

Abstract

Monoecious, polygamous, or dioecious annual or perennial herbs with milky juice, glabrous to stellate pubescent, with floating leaves or emergent, in fresh or brackish waters. Roots fibrous, septate or aseptate, at base of stem or lower nodes. Stems short, erect, cormlike, often with rhizomes, the rhizomes occasionally terminated by tubers, the apices without turions. Leaves basal, sessile, or petiolate; petioles terete to triangular, with sheathing base, the sheath without auricles; blade linear, lanceolate, ovate to rhomboid, with or without pellucid dots or lines, the margins entire or undulate, the apex obtuse, acute, or acuminate, the base either without basal lobes and attenuate, or otherwise truncate, cordate, sagittate, or hastate, with parallel primary veins and reticulate secondary veins. Inflorescences scapose, mostly erect, rarely floating, forming racemes or panicles by verticillate branching, rarely umbellate, without a subtending spathe, bracteate, the bracts whorled, linear, entire, obtuse to acute. Flowers hypogynous, perfect or imperfect, subsessile to long-pedicellate; perianth actinomorphic, of 6 separate segments in 2 whorls, the outer 3 sepal-like, green, persistent, erect, and enclosing flower and fruit or spreading to reflexed, the inner 3 petal-like, delicate, caducous; stamens free, 6, 9, or numerous; if 6, then in pairs alternating with the petals; if 9, then in 2 whorls with outer whorl of 6 and inner whorl of 3; if many, densely but irregularly spaced; anthers tetrasporangiate, extrorse, basifixed or versatile, dehiscing by longitudinal slits; carpels 6-many, free, in 1 whorl or irregularly spaced, each with 1(−2) anatropous basal ovules, rarely (Damasonium) 2-many on marginal placentae; styluli terminal or lateral; stigma linear. Fruits achenes or rarely follicles, mostly numerous. Seeds 1-few, U-shaped; endosperm absent in mature seeds.