Najas gracillima
Thread-leaved water-nymph, Thread-Leaved Water-Nymph
(c) Kim, Hyun-tae, some rights reserved (CC BY), uploaded by Kim, Hyun-tae · licence
Family: Hydrocharitaceae · Type: Herb · Not Native
Najas gracillima (Thread-leaved water-nymph) is a non-native California herb in the Hydrocharitaceae family, recognized by lowest leaf tooth count and truncated sheath tips.
Thread-leaved water-nymph is a naturalized annual aquatic plant found in northern Sacramento Valley rivers and lakes at elevations around 100 meters. Flowering from June to August, this delicate plant produces tiny, inconspicuous flowers with subtle reproductive structures. Growing as a monoecious plant with slender stems, it spreads through aquatic environments with fine, thread-like vegetative characteristics. Its narrow leaves feature 13 to 17 teeth along each margin, with acute tips and a distinctive truncate sheath. The small seeds are fusiform-shaped, with a pitted, dull coat measuring 0.4 to 0.7 millimeters long.
Identification and appearance
Key characters: 2 sympatric species; distinguished by lowest leaf tooth count and truncated sheath tips
Habitat and range
Habitat: Rivers, lakes
Elevation: +- 100 m.
Outside California: native to northeastern United States, Eurasia
Bloom period
Najas gracillima blooms Jun-Aug.
How to tell it apart
vs Hydrilla: Najas leaves have obvious teeth along margins; Hydrilla has spiny bumps on the leaf midrib underneath.; vs Elodea: Najas leaves are arranged opposite or in whorls of many; Elodea has 2-3 leaves at stem base, 3-7 higher up.; vs Egeria: Najas has tiny leaves under 1.5 cm; Egeria leaves are much larger (1.2-4 cm long).; vs Ottelia: Najas is completely submerged with tiny flowers; Ottelia has floating leaves and showy white flowers above water.; vs Limnobium: Najas is fully submerged with narrow toothed leaves; Limnobium has round floating leaves on spongy stalks.
Frequently asked questions
Is Najas gracillima native to California?
No. Najas gracillima is not native to California (recorded as not native).
When does Najas gracillima bloom?
Najas gracillima blooms Jun-Aug.
What plant family does Najas gracillima belong to?
Najas gracillima is in the Hydrocharitaceae family, genus Najas.
What habitat does Najas gracillima grow in?
Najas gracillima grows in Rivers, lakes.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.