Potamogeton pusillus L.

Potamogetonaceae, J.J. Symoens. Flora of Tropical East Africa. 2006

Morphology General Habit

Submerged aquatic herb.

Vegetative Multiplication Rhizomes

Rhizomes absent or only present later in the growing season,annual to biennial, filiform, terete, with short internodes.

Morphology Stem

Stems annual to perennial, up to 1 m long, 0.3– 0.7(– 1) mm in diameter, terete or compressed, sparingly to much branched. Stem anatomy:stele of the circular type; endodermis of the O-type; interlacunar bundles absent; subepidermal bundles present; pseudo-hypodermis mostly absent, if present 1-layered.

Morphology General Buds

Turions, when present, mostly sessile and axillary, but sometimes terminal on axillary branches, rigid, fusiform, with a few erect, patent or recurved free leaves.

Morphology Leaves

Submerged leaves bright green to olive green or dark green, sometimes with a brownish tinge, sessile, linear, (9– )20– 85(– 110) mm long, (0.3– ) 0.8– 2(– 2.5) mm wide, (15– )20– 90 times as long as wide, flaccid or firm, translucent, narrowly cuneate at base, tapering or rather abruptly narrowed to an acute or acuminate apex; margins entire, bordered by a narrow marginal vein; midrib occupying 15– 35 per cent of the leaf width at base, not bordered by lacunae or the lacunae poorly developed and restricted to the lower leaf half; lateral veins 1(– 2) on each side, distinct, joining the midrib 1.5– 4 leaf widths below the leaf apex; true floating leaves absent but rarely the uppermost leaves with lamina floating at the water surface, subsessile, linear-oblanceolate, 18– 38 mm long, 1.3– 3.1 mm wide, 7– 20 times as long as wide, bright green, narrowly cuneate at base, acute to narrowly obtuse at apex, 3– 5-veined, with broad rows of lacunae bordering the midrib; stipules axillary, connate and forming a tubular sheath at least in their lower part and when young, but splitting with age, 4– 18(– 32) mm long, translucent, persistent or decaying; turions mostly sessile and axillary, but sometimes also terminal on axillary branches, narrowlycylindrical, with a few erect, patent or recurved free leaves.

Morphology Reproductive morphology Inflorescences

Peduncles filiform to slightly clavate, ± flexuous, (6– )10– 30(– 55) mm long, 1– 6 times as long as the fruiting spike, as thick as the stem, slightly or distinctly compressed; spikes cylindrical, with 2– 7 flowers, in 1– 4 whorls, ± contiguous, sometimes the lowest flower remote, 4– 15 mm long in fruit.

Morphology Reproductive morphology Flowers

Tepals 0.8– 1.8 mm long, mostly persistent; carpels (3– )4(– 5); anthers 0.7– 0.9 mm long.

Morphology Reproductive morphology Fruits

Fruitlets obovoid, ± compressed, 1.8– 2.7 mm long, 1– 1.5 mm broad, green to pale olive, dorsally without keel, beak nearly centrally placed, straight or somewhat oblique, 0.2– 0.4 mm long.

Habitat

In lakes, dams and ponds, also in slow-flowing waters, sometimes in slightly brackish water; water depth 30– 60 cm; 600– 1700 m

Distribution

K3 K4 T7 U4 from Morocco to Libya and Egypt, also common in Europe and temperate parts of Asia, Arabia and North America, rarer in American and Asian tropics