Hippuris lanceolata
Observ. Bot. 3: 7, plate 1. 1783.
Stems 100–500 mm. Rhizomes 4–7 mm diam. Leaves on mid portions of emergent shoots in whorls of (5 or)6(or 7), linear to narrowly oblong or lanceolate, 5–20 × 0.5–1.5 mm, midvein inconspicuous, lateral veins present, sometimes obscure, ape× subacute, tip not curled in dried plants. Flowers bisexual; filaments equal to or shorter than anthers. Drupes 1.8–2 × 0.6–1.2 mm. 2n = 32 (Russian Far East).
Phenology: Flowering summer.
Habitat: Shallow fresh and brackish pools, pond margins.
Elevation: 0–300 m.
Distribution
Greenland, Man., Nfld. and Labr. (Labr.), N.W.T., Nunavut, Ont., Que., Yukon, Alaska, Eurasia.
Discussion
N. N. Tzvelev (1980) speculated that Hippuris lanceolata arose from hybridization between H. tetraphylla and H. vulgaris or their precursors. Although H. lanceolata is intermediate in some features, and is often misplaced with either H. tetraphylla or H. vulgaris, it is fertile and there is no indication of pollen abortion or failure of seed set. No transitional plants have been seen; hybrid origin appears unlikely. The range of H. lanceolata extends well north of that of either putative parent, especially that of H. vulgaris. Hippuris lanceolata is the sole species of Hippuris in some areas of the Arctic.
Selected References
None.