Potamogeton
| Potamogeton | |
|---|---|
 |
|
| Potamogeton perfoliatus | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Monocots |
| Order: | Alismatales |
| Family: | Potamogetonaceae |
| Genus: |
Potamogeton L. |
| Species | |
|
80–100, see text |
|
80–100, see text
Potamogeton is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed (Elodea canadensis). The genus name means "river neighbor", originating from the Greek potamos (river) and geiton (neighbor).
Potamogeton species range from large (stems of 6 m or more) to very small (less than 10 cm). Height is strongly influenced by environmental conditions, particularly water depth. All species are technically perennial, but some species disintegrate in autumn to a large number of asexually produced resting buds called turions, which serve both as a means of overwintering and dispersal. Turions may be borne on the rhizome, on the stem, or on stolons from the rhizome. Most species, however, persist by perennial creeping rhizomes. The leaves are alternate, which contrasts with the closely related genus Groenlandia, where the leaves are opposite or whorled.
In many species, all the leaves are submerged, and in these cases, they are typically thin and translucent. Some species, especially in ponds and very slow-moving waters, have floating leaves which tend to be opaque with a leathery texture.
All Potamogeton have a delicate membranous sheathing scale, the stipule, at the leaf axil. This may be wholly attached, partly attached, or free of the leaf, and it may have inrolled margins or appear as a tube. The morphology of the stipule is an important character for species identification. The flowers, which are often overlooked, are greenish-brown and are composed of four rounded segments borne in a spike. The fruits are spheroidal and green to brown, usually 1–3 mm in diameter, with a noticeable 'beak'.
Most fine-leaved pondweeds are diploid, with 2n = 26 (such as P. pusillus or P. trichoides) or less commonly 28 (P. compressus, P. acutifolius). Broad-leaved taxa are mainly tetraploid, with 2n = 52 (e.g. P. alpinus, P. praelongus), but a few species are diploid (e.g. P. coloratus or octaploid (2n = 104)(e.g. P. illinoensis).
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