Jepson Flora Project: Jepson Interchange    

 
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  • Up-to-date information about California vascular plants is available from the Jepson eFlora.

HYDROCHARITACEAE

WATERWEED FAMILY

Robert F. Thorne

Annual, perennial herb, aquatic, freshwater or marine, bisexual, monoecious, or dioecious
Leaves basal or cauline, alternate, opposite, or whorled, generally ± sheathing at base, glabrous
Inflorescence: cyme; flowers 1–few, subtended by ± sheathing, entire or lobed bract; staminate flowers sometimes deciduous, free-floating
Flower radial; perianth tube 0 or much elongated, peduncle-like in flower; sepals (0)3, green; petals (0)3, colored or white; stamens (1)3–many, generally in 1+ series; ovary inferior, chamber 1, placentas parietal or basal, ovules 1–many; style lobes generally 3, linear, lobed or notched
Fruit: achene or berry-like and dehiscing irregularly, linear to spheric, submersed
Genera in family: ± 17 genera, ± 130 species: worldwide; some cultivated for aquaria, others noxious weeds.

HYDRILLA


Species in genus: 1 sp
Etymology: (Greek: growing in water)

Introduced

H. verticillata (L.f.) Casp.

Perennial, rooting at nodes, submersed, dioecious
Stems: horizontal, tuber-like; erect stems elongate, much-branched
Leaves whorled, generally 4–8 per whorl, sessile, 1–2 cm, 1.5–2 mm wide, oblong, margin clearly, sharply toothed, midrib ± keeled below, rough, with tooth-like, conic bumps, tip generally sharp-pointed
Staminate inflorescence: flower 1, bract at base of elongated perianth tube, spheric
Pistillate inflorescence: flower 1, bract at base of elongated perianth tube, ± cylindric
Staminate flower deciduous, free-floating; perianth parts 6 in 2 whorls, 3–5 mm; stamens 3
Pistillate flower persistent, floating; perianth parts 6 in 2 whorls, 3–5 mm; stigmas 3
Fruit 5–6 mm, ± fusiform
Ecology: Ditches, canals, ponds, reservoirs, lakes
Elevation: < 200 m.
Bioregional distribution: Inner North Coast Ranges, n&c Sierra Nevada Foothills, Sacramento Valley, South Coast, Desert
Distribution outside California: to s US, C.America.; native to Eurasia
Weedy.

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