Potamogeton schweinfurthii A.Benn.

Rooted aquatic herb, with submerged and floating leaves.. Rhizomes perennial, slender, terete,white, with apical winter buds.. Stems annual, sparingly to much branched, slender, terete, up to 3.5 m long, ± spongy; specialized dormant turions not developing.. Submerged leaves almost always present, the young ones yellow-green or brownish, the old ones bright green or dark olive-green, often with a reddish or brownish tinge, sessile to shortly petiolate, often incrusted with calcium carbonate; petiole 0– 30(– 82) mm long; lamina narrowly lanceolate to oblong-elliptical, sometimes that of the lower leaves reduced to phyllodes, 45– 190(– 260) mm long, (3– )7– 28 mm wide, 4– 70 times as long as wide, membranous and translucent, cuneate, acute to mucronate, 5– 11(– 13)-veined, with or without narrow rows of lacunae bordering the midrib, margins often slightly undulate, entire or bearing very minute hyaline teeth; intermediate leaves sometimes present, instead of floating leaves; floating leavesabsent or present, yellow-green to dark green, with a reddish tinge; petiole (14– )30– 70(– 200)mm long, never discoloured at junctionwith the lamina; lamina narrowly oblong to elliptical or ovate, 43– 130 mm long, 12– 30 mm wide, 2– 6 times as long as wide, opaque, subcoriaceous to coriaceous, 11– 21-veined, entire, mostly narrowly cuneate at base, obtuse to acute; stipules axillary, convolute, 20– 62 mm long, translucent, acute, persistent.. Peduncles mostly terminal or lateral in the axils of submerged leaves, sometimes in the axils of floating leaves, 35– 250 mm long, 2– 3 times as long as the fruiting spike, thicker than the stem; spikes emergent, cylindrical, 30– 90 mm long when in fruit, contiguous.. Flowers numerous, sepals pale greeny brown; anthers yellow green; carpels 4; stigmas whitish becoming mauve-brown.. Fruitlets pale brown-green, 2.9– 3.9(– 4.1) mm long, 2– 2.5 mm wide, ventrally nearly straight; dorsal keel distinct, lateral keels sometimes present; beak short, obtuse.. Stem anatomy: stele of the trio type, rarely of the proto or oblong type, endodermis of the U-type, interlacunar bundles present, in 1 circle (rarely 2, one being incomplete), subepidermal bundles absent or scattered ones present, pseudohypodermis present, 1-layered.. Fig. 3 (p. 11).