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Published In: Species Plantarum 1: 126. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 8/4/2009)

 

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1. Potamogeton L. (pondweed)

Plants perennial, glabrous. Stems diffuse, highly branched, rooting at lower nodes. Leaves alternate, sometimes appearing opposite or tufted, filiform to ovate or elliptic, sometimes differentiated into floating and submerged leaf types. Stipules present or sometimes degraded at maturity, free and appearing axillary, sometimes partially or totally fused to the petiole forming an open sheath or sometimes free from the leaf base but forming a sheath that clasps the stem. Inflorescences axillary or terminal spikes, the peduncle not becoming coiled during maturation of the fruits. Flowers perfect, minute. Perianth of 4 tepals, these narrowed to a claw. Stamens 4, opposite the tepals and fused to the tepal bases, the filaments absent or nearly so. Gynoecium of 4 separate pistils, the ovaries superior, the style lacking or short, the stigma 1. Ovules 1 per ovary. Fruits achenes or drupelike, often somewhat flattened and sometimes beaked and/or keeled, the embryo usually somewhat cuved or coiled. About 90 species, worldwide.

The linear‑leaved species of Potamogeton are sometimes confused with those of Najas and Zannichellia. Leaves of both these other genera are mostly opposite or whorled, rather than alternate, and those of Najas further differ in having toothed margins (sometimes visible only under magnification).

The pondweeds are all aquatic, varying from submerged species to those with floating leaves. Plants of some taxa sometimes occur emergent on mudflats and lakeshores. The spikes of Potamogeton are usually held just above the water surface, or less commonly are submerged. The flowers are variously adapted to pollination by wind or by water. The fruits and foliage provide food for various kinds of wildlife, and the plants also provide cover for fish and other aquatic animals.

 

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1 Submerged leaves variously shaped, but more than 5 mm wide (2)
+ Submerged leaves linear, less than 4 mm wide (7)
2 (1) Leaf margins sharply and finely toothed (visible without magnification) and strongly undulate; fruits with a conical beak 2.0–2.5 mm long and a toothlike basal appendage on the back 2 Potamogeton crispus
+ Leaf margins entire or minutely toothed only near the tip, sometimes undulate or finely crinkled (thus appearing toothed); fruits with beaks lacking or if present then less than 1.5 mm long and the fruit without a basal appendage (3)
3 (2) Stems and petioles with scattered purplish black spots 9 Potamogeton pulcher
+ Stems and petioles without dark spots (4)
4 (3) Largest submerged leaves with 25–39 main veins, usually strongly folded logitudinally; fruits 4.5–5.0 mm long, including the beak 1 Potamogeton amplifolius
+ Largest submerged leaves with 5–19(–25) main veins, flat or only slightly folded near the base; fruits 2.5–4.0 mm long, including the beak (5)
5 (4) Stipules 1–3 cm long; submerged leaf blades less than 10 mm wide; floating leaves usually produced, narrowly elliptic to spathulate or obovate; stems somewhat flattened 4 Potamogeton epihydrus
+ Stipules 4–10 cm long; leaves various; stems round in cross-section or nearly so (6)
6 (5) Largest submerged leaves with petioles 4–13 cm long, the leaf blades 4–22 mm wide; floating leaves mostly narrowly oblong to narrowly elliptic 7 Potamogeton nodosus
+ Submerged leaves all sessile or with petioles to 2 cm long, the leaf blades 20–50 mm wide; floating leaves absent or ovate to broadly oblong 6 Potamogeton illinoensis
7 (1) Submerged leaves 2.5–4 mm wide, with 5–13 main veins; floating leaves usually produced; stems somewhat flattened 4 Potamogeton epihydrus
+ Submerged leaves 0.2–2.5 mm wide, with 1 or 3 main veins; floating leaves absent or sometimes produced (in P. diversifolius); stems round in cross-section (except sometimes in P. foliosus) (8)
8 (7) Stipules or stipular sheath free from the leaf base, appearing axillary or sometimes partially sheathing the stems (9)
+ Stipular sheath of submerged leaves fused to the leaf base, the tip free, projecting from the leaf (the leaf appearing to arise from the middle or near the tip of the sheath, which may also be partially clasping the stems) (10)
9 (8) Fruits with an undulate, winglike keel, the sides rounded or more often concave; nodes of the stem usually without a pair of minute glands 5 Potamogeton foliosus var. foliosus
+ Fruits with the backs rounded to acute, but lacking a winglike keel, the sides rounded; nodes of the stem usually with a pair of minute glands 10 Potamogeton pusillus var. pusillus
10 (8) Fruits strongly flattened; elliptic-lanceolate to nearly orbicular, long-petiolate floating leaves often produced 3 Potamogeton diversifolius
+ Fruits rounded on the sides; floating leaves not produced 8 Potamogeton pectinatus
 
 
 
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