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Herbs, perennial or rarely annual, aquatic or of marshes, sometimes rhizomatous. Leaves basal, linear, lanceolate, elliptic to ovate or orbicular, or sagittate, with elongated sheathing petioles; principal veins parallel with margins and converging toward apex and connected by transverse veins. Flowers often whorled at nodes of scape forming racemes, panicles, or umbels, pedicellate, actinomorphic, bisexual, unisexual, or polygamous, usually bracteate. Sepals 3, persistent, green. Petals 3, deciduous, usually white, sometimes yellowish. Stamens 3 to numerous, whorled, with elongated filaments; anthers 2-celled, extrorse, opening by longitudinal slits. Carpels 3 to numerous, whorled or spirally arranged, free; ovules 1 to several; style persistent. Fruit a cluster or whorl of laterally compressed achenes, drupelets, or occasionally follicles. Seeds curved, with a horseshoe-shaped embryo; endosperm absent.
About 13 genera and ca. 100 species: cosmopolitan, especially abundant in temperate and tropical regions of the N Hemisphere; six genera (one introduced) and 18 species (three endemic, one introduced) in China.
Chen Yaodong. 1992. Alismataceae. In: Sun Xiangzhong, ed., Fl. Reipubl. Popularis Sin. 8: 127-145; Zhou Lingyun. 1992. Butomopsis and Limnocharis. In: Sun Xiangzhong, ed., Fl. Reipubl. Popularis Sin. 8: 147-151.Chen Yaodong. 1992. Alismataceae. In: Sun Xiangzhong, ed., Fl. Reipubl. Popularis Sin. 8: 127-145; Zhou Lingyun. 1992. Butomopsis and Limnocharis. In: Sun Xiangzhong, ed., Fl. Reipubl. Popularis Sin. 8: 147-151.
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| 1 | Stamens 8 or 9, or numerous, with sterile staminodes in outermost whorl, filaments flattened; stigmas sessile, carpels 6-9 or numerous, crowded into a head; aquatic herbs with terminal umbels; bracts forming an involucre | (2) | | + | Stamens 3 to numerous; style persistent, carpels few to numerous; aquatic or marsh herbs with racemes, panicles, or umbels | (3) | | | | | | 2(1) | Petals white; stamens 8 or 9; carpels 6-9; pedicels slender. | 5 Butomopsis 拟花蔺属 | | + | Petals yellowish; stamens numerous; carpels numerous; pedicels thick. | 6 Limnocharis 黄花蔺属 | | | | | | 3(1) | Flowers unisexual or polygamous. | 1 Sagittaria 慈姑属 | | + | Flowers bisexual | (4) | | | | | | 4(3) | Stamens 6; carpels arranged in a single whorl. | 4 Alisma 泽泻属 | | + | Stamens (6-)9 to numerous; carpels spirally arranged | (5) | | | | | | 5(4) | Inflorescences much branched, paniculate; fruitlets drupaceous, swollen, with woody endocarp and spongy exocarp. | 3 Caldesia 泽薹草属 | | + | Inflorescences unbranched, flowers usually solitary or up to 3 in inflorescence; fruitlets achenelike, laterally compressed. | 2 Ranalisma 毛茛泽泻属 | | | | |
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