Home
Stems sparingly branched distally, to 35 cm ´ 0.2--0.5 mm; internodes 0.4--1.9 cm, without prickles. Leaves spreading to ascending with age, 0.8--2 cm, lax in age; sheath 1--1.5 mm wide, apex deeply auriculate; blade 0.5--1 mm wide, margins minutely serrulate, teeth 40 per side, apex acute with 2--3 teeth, teeth unicellular; midvein without prickles abaxially. Flowers 1--2 per axil, staminate and pistillate on same plants. Staminate flowers in distal axils, 2--3 mm; involucre beaks 4-lobed, 1--1.5 mm; anther 4-loculed, 1.5 mm. Pistillate flowers distal to proximal, to 3.5 mm; styles to 1 mm; stigmas 2-lobed. Seeds not recurved, greenish brown, fusiform, 1.7--2.5 ´ 0.4--6 mm, apex with style situated at center; testa dull, 3 cell layers thick, pitted; aeroleareoles regularly arranged in 35 longitudinal rows, not ladderlike, 4-angled, as long aser than broad, end walls slightly raised. 2n = 24, 36, 48 (Asia).
Stems 10-20 cm tall, 0.5-1 mm in diam. Leaves narrowly linear to linear, 1-2.5 cm × 0.4-1 mm; sheath 1.5-3 mm, deeply auriculate; auricles narrowly triangular or lanceolate, 1-2 mm, serrulate with several teeth on each side, apex acute; leaf margin minutely and densely serrulate with 30-50 inconspicuous teeth on each side, consisting of brownish spine cells only. Plants monoecious; flowers solitary, or sometimes 2 or 3 together. Male flowers usually more toward upper axils, ca. 1 mm, elliptic; spathe absent; anther 4-thecous. Female flowers 1.5-2 mm; style ca. 1 mm; stigmas 2-4-lobed. Fruit oblong, 1.5-2 × ca. 0.8 mm. Seeds ellipsoid-oblong, with ca. 30 rows of pits; areoles hexangular and irregularly polygonal toward ends, or rectangular. Fl. and fr. Jun-Sep. 2n = 12*, 24, 36*, 48, 72.
Small, unarmed plants with much branched shoots, 10-60 cm long, often plumose above because of the closely packed leaves. Roots many, long, filiform, with a dense covering of long root-hairs towards the tip. Stems with terete, brittle internodes, 1 mm in diam. Leaves 16-25 mm long, 0.5-6 mm wide, teeth microscopic, about 40-55 on each side; sheaths with linear-setaceous auricles about 1.5 mm long, bearing some minute teeth. Flowers monoecious. Male flowers solitary, in upper leaf axils, naked; pedicel at anthesis 1 mm long, anther 1 mm long, oblong, apically with 2 small obtuse ridges. Female flowers usually in lower axils, sessile, about 1.5 mm long, the ovary about as long as the short style and the 2 long stigmatic arms. Fruit oblong, 1.5 mm.
An annual herb. It attaches to the ground but grows underwater in freshwater lakes. The stems are 35-40 cm long and 0.7 mm thick. The leaves are 14-25 mm long and 1 mm wide. There are 2-3 teeth at the tip.
Perennial aquatic herb, shoots 100-600 mm long. Stems smooth, herbaceous. Leaves filiform with 40-60 microscopic teeth, septa of leaf distinct. Stigmas 2. Flowers green.
