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Robert F. Thorne, C. Barre Hellquist & Robert R. Haynes

Annual, perennial herb, aquatic, freshwater or marine, glabrous or hairy; monoecious, dioecious, or flowers bisexual. Leaf: basal, alternate, opposite, or whorled, generally sessile, generally ± sheathing at base. Inflorescence: axillary, terminal, or scapose, cyme or flowers 1, subtended by ± sheathing, entire or lobed bract; staminate flowers sometimes deciduous, free-floating. Flower: generally radial; perianth 0 or tube 0 or elongate, peduncle-like in flower; sepals (0)3(4), green; petals (0)3(4), white or not; stamens (0)2–many, generally in 1+ series; ovary inferior, chamber 1 or falsely 6–9, placentas parietal, ovules 1–many, style lobes generally 3, linear, lobed or notched. Fruit: achene or berry-like and dehiscing irregularly, linear to spheric, submersed.
± 17 genera, ± 130 species: worldwide; some cultivated for aquaria, others noxious weeds. [Haynes 2000 FNANM 22:26–38] Ottelia alismoides (L.) Pers. is a possibly extirpated alien. —Scientific Editor: Thomas J. Rosatti.
Unabridged references: [Les, D. H. [et al. 2006], Moody, M. L., & Soros, C. L. 2006. A reappraisal of phylogenetic relationships in the monocotyledon family Hydrocharitaceae (Alismatidae). Pp. 211–230, in Columbus, J. T., Friar, E. A., Porter, J. M., Prince, L. M., & Simpson, M. G. (eds), Monocots: Comparative Biology and Evolution. Excluding Poales. Rancho Santa Ana Botanical Garden, Claremont, Ca. [Aliso 22: 211–230.]; Tanaka, N., Uehara, K., & Murata, J. 2004. Correlation between pollen morphology and pollination mechanisms in the Hydrocharitaceae. J. Plant Res. 117:265–276]

Key to Hydrocharitaceae

Perennial herb, submersed, rooted in mud; dioecious. Stem: slender, branched or not. Leaf: opposite below, crowded and in whorls of 3–6 above, sessile, finely to coarsely serrate. Staminate inflorescence: axillary, sessile; flowers 2–4(5), 1 open at a time; bract slender. Pistillate inflorescence: [axillary, sessile; flower 1; bract slender, ± tubular]. Staminate flower: floating; pedicel elongate, peduncle-like, persistent on plant; stamens 9. Pistillate flower: [floating; perianth tube elongate, peduncle-like; stigmas 3, 3–4-lobed].
2 species: South America. (Latin: mythical water nymph) Only staminate plants observed outside native range. Egeria najas Planch. <Noxious weed> expected but not yet found.

E. densa Planch.
Stem: 2–3 mm thick. Leaf: 1.2–4 cm, 2–5 mm wide, recurved, narrowly oblong, finely serrate. Staminate flower: pedicel <= 8 cm; petals 8–10 mm, white, ± round. Pistillate flower: [as staminate; petals 6–7 mm].
2n=46. Streams, ponds, sloughs; < 2200 m. Sierra Nevada Foothills, Great Central Valley, San Francisco Bay Area, San Jacinto Mountains, Great Basin Floristic Province; to eastern United States; Europe; native to South America. [Elodea densa (Planch.) Casp.] Staminate plants widely cultivated for aquaria. Jul–Aug {Noxious weed} [Online Interchange]

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora,, accessed on Dec 1 2015
Citation for this treatment: [Author of taxon treatment] 2013. Egeria, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on Dec 1 2015

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Geographic subdivisions indicated for the distribution of Egeria densa Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).

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Data provided by the participants of the Consortium of California Herbaria.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.