Callitriche marginata
California water starwort
Photo by Chez Brungraber
Family: Plantaginaceae · Type: Herb · Native
Callitriche marginata (California water starwort) is a native California herb in the Plantaginaceae family, recognized by fruit shape (wider than long) and large leaves.
California water starwort is a California native perennial found in the California Floristic Province in shallow water environments, becoming stranded in vernal pools at elevations up to 1,500 meters. Flowering from March to June, this delicate aquatic plant produces tiny white flowers in small clusters along its slender stems. Growing with fine, thin branches that spread across water surfaces, it forms dense, low-growing mats just above or at water level. Its leaves are distinctively oblong to spoon-shaped, measuring 4 to 7 millimeters long and less than 1.5 millimeters wide, creating a delicate green network across wet habitats. The small fruits are black when mature, measuring approximately 1 millimeter wide, with an extremely narrow wing barely visible at the fruit's edges.
Identification and appearance
Key characters: Co-occurs with 7 species; fruit shape (wider than long) and large leaves are diagnostic
Habitat and range
Habitat: Becoming stranded (often in vernal pools)
Elevation: < +- 1500 m
California counties: Stanislaus, Riverside, Monterey, Solano, San Luis Obispo, Kern, Shasta, Calaveras, San Diego, Orange, Mendocino, Sutter, Los Angeles, Tulare, Ventura, Santa Cruz, Colusa, San Bernardino, Sacramento, Santa Barbara, Yolo, Sonoma, Marin, Merced, Butte, Tehama, Placer, Glenn, Yuba, Contra Costa, Napa, Alameda, Humboldt, Santa Clara, San Mateo, Fresno, San Joaquin, Madera, Sierra, Lake, Tuolumne
Outside California: to British Columbia, Baja California
Bloom period
Callitriche marginata blooms Mar-Jun.
How to tell it apart
vs Nasturtium: Nasturtium has bright yellow or white 4-petaled flowers; Callitriche has no petals, just tiny styles.; vs Lemna: Lemna is free-floating duckweed with no roots in substrate; Callitriche is rooted with opposite-leaved stems.; vs Ludwigia: Ludwigia has showy yellow flowers and consistent leaf shape; Callitriche lacks petals and has dimorphic leaves.; vs Soleirolia: Soleirolia is terrestrial with round leaves; Callitriche is aquatic with narrow or spoon-shaped leaves.; vs Stellaria: Stellaria has notched white petals on terrestrial plants; Callitriche lacks petals and forms aquatic rosettes.
Frequently asked questions
Is Callitriche marginata native to California?
Yes. Callitriche marginata is native to California (recorded as native).
When does Callitriche marginata bloom?
Callitriche marginata blooms Mar-Jun.
Where in California does Callitriche marginata grow?
Callitriche marginata occurs in Stanislaus, Riverside, Monterey, Solano, San Luis Obispo, Kern, Shasta, Calaveras and other counties, at elevations of < +- 1500 m.
What plant family does Callitriche marginata belong to?
Callitriche marginata is in the Plantaginaceae family, genus Callitriche.
What habitat does Callitriche marginata grow in?
Callitriche marginata grows in Becoming stranded (often in vernal pools).
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · 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.