Potamogeton L., Sp. Pl. ed.1: 126. 1753; Gen. Pl. ed. 5: 61. 1754; Hook. f., Fl. Brit. India 6: 565. 1894; Fl. China @ eFloras.org 23: 108; Fl. North Amer. @ eFloras.org vol. 22; Fl. Pak. @ eFloras.org p. 1.

Perennial or annual herb, in fresh water, totally submerged or with floating leaves. Stem terete or compressed. Leaves submerged or floating, alternate or imperfectly opposite, mono- or dimorphic, submerged leaves sessile or petiolate, linear with thin blades, lanceolate, margin entire, denticulate or serrulate; floating leaves petiolate with leathery blades, lanceolate to ovate or broadly elliptic-oblong. Stipules membranous, connate or free, if free, then convolute, tubular, sheathing stem and young inflorescences. Inflorescence a pedunculate spike, terminal or axillary, surrounded by stipular sheath in bud, emergent or floating or submerged at anthesis. Flowers ebracteate, small, tetramerous, actinomorphic. Tepals 4, free, concave, smooth, bract-like, obovate, clawed, each inserted opposite the stamen. Stamens 4, opposite and united with tepals at base; filaments absent; anthers bithecous, extrorse, dehiscence longitudinal. Carpels 1-5, usually 4, free; stigmas sessile or on short styles, expanded, capitate or peltate; ovules solitary, attached to adaxial side of carpel. Fruitlets drupaceous with fleshy exocarp and bony endocarp containing solitary seed.

90 species

Potamogeton nodosus Poir. in J.B.A.M. de Lamarck et al., Encycl. Method. Bot., Suppl. 4(2): 535. 1816; Fl. China @ eFloras.org 23: 114; Fl. North Amer. @ eFloras.org vol. 22; Fl. Pak. @ eFloras.org p. 3; P. indicus Roxb., Fl. Ind. 1: 452. 1820.

Plants perennial, fresh water, rhizomatous. Stem usually simple, occasionally branched, terete, ca. 2 mm diameter. Leaves dimorphic: submerged and floating, spirally arranged. Submerged leaves petiolate, lax, petiole 2-7.5 cm long; lamina lanceolate to broadly lanceolate-oblong, 6-13 cm x ca. 4 cm, thin, translucent. Floating leaves petiolate, petiole 3-7 cm long; leaf blade 5-11 cm x 3-5.5 cm, broadly ovate to elliptic, coriaceous, margin entire, base cuneate to rounded, apex acute to slightly obtuse, veins 9-21. Stipules membranous, brownish, free, keeled, lanceolate, 4-5.5 cm x 0.9-1 cm. Inflorescence pedunculate spike, axillary when young surrounded by stipular sheath, emergent at anthesis. Spike cylindric, 4-4.5 cm x 0.6-0.9 cm; peduncle 7-8 cm long and thicker than stem. Spike densely flowered, flowers in whorls, ebracteate, tetramerous, sessile, small. Tepals 4, free, small, obtuse, entire, ca. 1.5 mm long, clawed. Stamens 4, opposite and adnate to base of tepals, filaments absent, anthers bithecous, dehiscence longitudinal. Carpels 4, free, erect and parallel, stigmas short, style very short or absent, ovary with solitary ovule attached laterally. Fruitlets 4, drupaceous, fully or incompletely developed, brownish or reddish, obovoid, 3-4 cm x 2-3 mm, exocarp fleshy, endocarp bony, with solitary seed, abaxial keel distinct, beak erect.

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