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

M. Thulin et al. Flora of Somalia, Vol. 1-4 [updated 2008] https://plants.jstor.org/collection/FLOS

Morphology General Habit

Submerged perennial with poorly developed slender rhizome, or arising from seeds or detached buds

Morphology Stem

Stems 20–100 cm long, strongly branched from the base; internodes of relatively equal length

Morphology Leaves

Leaves translucent, narrowly linear, 2–8 cm long and 1–2.5 mm wide, with 1 prominent midrib and 1(–2) weaker nerves on each side of the midrib, apiculate at the tip; sheath 5–18 mm long, tubular for more than half the length when young, later splitting almost to the base, light brown, semipersistent

Morphology Reproductive morphology Inflorescences

Spikes axillary, 4–12 mm long, 2–15-flowered, rarely interrupted; peduncles 1–3 cm long

Morphology Reproductive morphology Fruits

Fruit 2–2.5 x 1–1.5 mm, green to olive, obovoid and compressed with convex margins; keel obscure, rounded, smooth; beak 0.3–0.4 mm long, straight or somewhat oblique, almost centrally placed.

Distribution

N2 (“Medishe Springs”) scattered in Africa, more common in Europe and temperate parts of Asia and North America.

Ecology

Altitude c. 1800 m.

Distribution

Biogeografic region: Andean. Elevation range: 2200–3919 m a.s.l. Native to Colombia. Colombian departments: Antioquia, Bogotá DC, Boyacá, Cundinamarca, Risaralda, Santander.

Habit

Herb, Aquatic.

Conservation

IUCN Red List Assessment (2021): LC.

IUCN Red List of Threatened Species https://www.iucnredlist.org/species/163982/120218868

Conservation

LC - least concern

Bernal, R., Gradstein, S.R. & Celis, M. (eds.). 2015. Catálogo de plantas y líquenes de Colombia. Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá. http://catalogoplantasdecolombia.unal.edu.co

Distribution

Nativa en Colombia; Alt. 2200 - 3919 m.; Andes.

Morphology General Habit

Hierba, acuática

Conservation

No Evaluada

J. R. Timberlake, E. S. Martins (2009). Flora Zambesiaca, Vol 12 (part 2). Royal Botanic Gardens, Kew

Type

Type from Europe (LINN 175.15, left hand specimen chosen as lectotype by Dandy & Taylor in J. Bot. 76 92, 1938).

Morphology General Habit

Submerged aquatic herb

Vegetative Multiplication Rhizomes

Rhizomes absent or only present later in 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 wide, terete or compressed, sparingly to much branched; turions when present mostly sessile and axillary, but sometimes terminal on axillary branch, rigid, narrowly cylindrical or fusiform with a few erect, spreading or recurved free leaf Stem anatomy stele of circular type, endodermis of O-type; interlacunar bundles absent, subepidermal bundles present; pseudo-hypodermis mostly absent, if present 1-layered.

Morphology Leaves

True floating leaf absent but rarely the uppermost leaf with lamina floating at the water surface, subsessile, linear- oblanceolate, 18–38 1.3–3.1 mm, 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 Submerged leaf sessile, linear, (9)20–85(110)  0.3)0.8–2(2.5) mm, (15)20–60(90) times as long as wide, flaccid or firm, translucent, bright green to olive green or dark green, sometimes with a brownish tinge, 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% of leaf width at base, not bordered by lacunae or 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 leaf apex

Morphology Leaves Stipules

Stipules axillary, joined, forming a tubular sheath for most of their length when young, but splitting with age, 4–18(32) mm long, translucent, persistent or decaying

Morphology Reproductive morphology Inflorescences Peduncles

Peduncles filiform to slightly club-shaped, ± flexuous, (6)10–30(55) mm long, 1–6 times as long as fruiting spike, as thick as stem, slightly or distinctly compressed

Morphology Reproductive morphology Inflorescences

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 Tepal

Tepals 0.8–1.8 mm long, mostly persistent; carpels (3)4(7)

Morphology Reproductive morphology Flowers Androecium Stamens Anthers

Anthers 0.7–0.9 mm long

Morphology Reproductive morphology Fruits

Fruitlets obovoid, ± compressed,1.8–2.7(3.3) mm long, 1–1.5 mm broad, green to pale olive, without dorsal keel; beak centrally placed, straight or somewhat oblique, 0.2–0.4 mm long

Distribution

Caprivi, Zambia, Zimbabwe, Mozambique, Malawi. Across Africa from Azores and Canary Is., North Africa and tropical NE and E Africa to Congo, Namibia and South Africa; also common in Europe and temperate parts of Asia and North America, rarer in the American and Asian tropics, including New Guinea.

Ecology

Mostly in disturbed places (ditches, ponds, reservoirs) and slow- flowing waters from 30–60 cm deep, sometimes in lightly brackish water; 600–1750 m, up to 2900 m in Ethiopia.

Conservation

Conservation notes Widely distributed; not threatened.

Recognition

P. pusillus is a very polymorphic species, varying greatly in leaf length, the number of leaf nerves and rows of lacunae along the midrib, shape of leaf apex, and number of flower whorls in the inflorescence. Owing to the lack of a consistently correlated set of morphological characters, no discrimination of infraspecific taxa based on these criteria seems possible. The united stipules forming a tubular sheath, at least when young, differentiate P. pusillus from P. berchtoldii Fieber from northern temperate regions, which has stipules open throughout their length.