Jepson Flora Project: Jepson Interchange    

 
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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.

NAJAS

Annual, aquatic, submersed, sometimes mat-like, monoecious or dioecious
Stems several, much-branched, slender
Leaves simple, cauline, opposite or appearing ± whorled; sheath generally wider than blade, expanded abruptly at junction with blade; blade generally linear, margin entire to spiny
Inflorescence axillary; flowers 1–few, clustered, inconspicuous
Staminate flower: perianth 0; stamen 1, anther opening irregularly, subsessile, subtended by 2 minute involucres, inner membranous, flask-shaped, outer cup-like, tubular, or with free scales
Pistillate flower: perianth part 0–1; ovary 1, chamber 1, ovule 1, style short, stigmas 2–4, linear
Fruit: achene, fusiform; outer wall thin, ± translucent
Species in genus: ± 50 species: ± worldwide
Etymology: (Greek: water nymph)
Reference: [Shaffer-Fehre 1991 Bot J Linn Soc 107:189–209]

Native

N. flexilis (Willd.) Rostk. & Schmidt

SLENDER WATER-NYMPH

Monoecious
Stem < 20 dm, much-branched
Leaves 1–2.5 cm, 1–2 mm wide, crowded on distal branches, flexible; sheath obtuse at junction with blade; blade margin minutely toothed, tip narrowly long-tapered
Staminate flower 2.5–3 mm; anther 1-chambered
Pistillate flower ± 3 mm; stigmas generally 3, sometimes 2–4
Fruit: surface smooth, shiny (finely net-like at 20X magnification)
Ecology: Uncommon. Ponds, lakes
Elevation: < 1500 m.
Bioregional distribution: Klamath Ranges, Inner North Coast Ranges (expected elsewhere)
Distribution outside California: to Canada, ne US, n Europe

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