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Delicate creeping herb, often much branched and forming dense patches, 1-15 cm long. Stipules minute, ovate-triangular, acutely acuminate, dentate, deciduous. Leaves opposite, ovate-oblong-lanceolate-spathulate, decurrent winglike along the petiole, obtuse, rounded or emarginate, entire, penninerved, with or without a row of distant glandlike hydathodes along the margin, 3½-15 by 1½-4 mm. Flowers sessile or obscurely pedicelled in one axil only of a pair of leaves; those of successive pairs alternately on the right and the left side of the stem. Sepals 2-3, half as long as the petals. Petals broadly oval, white or pink, 1-1¼ mm long. Stamens 3, in expanded flowers longer than the sepals. Stigmas 3, almost sessile, punctiform. Capsule subglobose, 1½-1¾ mm diam. Seeds oblong with rounded ends, faintly curved, yellowish brown, +-½ mm long.
Creeping or floating annual; lvs linear to obovate, 3–8 mm; fls mostly 3-merous; seeds axile, set at different levels in the fr, marked with transversely elongate, 6-sided areoles, the angular ends of the areoles dovetailed with those of adjacent rows, the longitudinal ridges appearing narrow or broken; 2n=ca 40. Three vars.: Var. triandra has linear to spatulate, often retuse lvs, and seeds with 16–26 areoles in each longitudinal row; Wis. and N.D. to Wash. and Calif., also in Eurasia, and intr. in Me. Var. americana (Pursh) Fassett has obovate, rarely retuse lvs, otherwise like var. triandra; muddy tidal shores, Que. and N.B. to Va., and also in Mo. Var. brachysperma (A. Gray) Fassett has obovate lvs, and seeds with 9–15 areoles in each longitudinal row; s. O. and c. Ill. to w. U.S.
Herbs, submersed, 2–10 cm. Stems prostrate, highly branched. Leaves light green to green; stipules triangular or ovate-lanceolate, 0.7–1 mm, margins dentate, apex acute or obtuse; petiole 0–3 mm; blade linear, lanceolate, or narrowly oblong, 3–10 × 1.5–3.5 mm, base attenuate, apex acute or obtuse. Pedicels 0.3–0.4 mm, erect. Flowers: sepals (2–)3(–4), usually 1 reduced, ovate, 0.5(–0.7) × 0.2–0.4 mm; petals 3, white or reddish, widely ovate or elliptic, 0.6–1.2 × 0.5 mm; stamens 3; styles 3. Capsules compressed-globose, 3-locular, 1.2–1.7[–2] mm diam. Seeds 10–25 per locule, oblong, straight or slightly curved, 0.4–0.5 × 0.1–0.2 mm; pits angular-hexagonal, length 2–3 times width, in 6–8 rows, 16–25 per row. 2n = ca. 40.
A small, soft creeping annual herb, rooting at the nodes. Leaves decussate, shortly petiolate, linear-oblong to narrowly ovate, up to 15 mm long and 3 mm broad, apex emarginate, narrowed at the base into a short petiole; Stipules membranous, deciduous. Flowers sessile or with pedicels up to 1 mm long. Sepals 3(rarely 2), narrowly ovate, 0.5 mm long. Petals 3, broadly ovate, 1-1.5 mm long, white or pink. Stamens 3, shorter than petals. Ovary 3-locular, globose, styles very short. Capsule membranous; seed slightly curved, oblong-terete, 0.5 mm, tesselate, light brown, shiny.
Leaves opposite, very shortly petiolate, 3–15 × 1–4 mm., ovate-oblong or linear-lanceolate, rounded or emarginate at the apex, cuneate at the base, entire, penninerved with 2–4 pairs of nerves; stipules minute, deciduous, ovate-triangular, margin undulate or dentate.
Small, soft, creeping annual herb, hydrophyte. Leaves decussate, apex emarginate. Flowers 3-merous, white or pink; January to February and in May.
A tender glabrous creeping annual herb, often much branched and rooting at the nodes; branches up to 15 cm. long.
Petals (2) 3, white or pink, 1–1·5 mm. long, ovate, apex obtuse, Stamens 3, slightly longer than the sepals.
Seeds c. 0·5 mm. long, yellowish-brown, oblong-cylindric, slightly curved.
Flowers sessile or obscurely pedicellate in the leaf-axils.
Sepals (2) 3, c. 0·5 mm. long, triangular, apex obtuse.
Ovary globose, with 3 minute spreading styles.
Capsule c. 1·5 mm. in diam., subglobose.
