Juncus dubius
Mariposa rush, Mariposa Rush
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Family: Juncaceae · Type: Grass · Native
Juncus dubius (Mariposa rush) is a native California grass in the Juncaceae family, recognized by dense mats, prominent scarious appendages, and complete crosswalls.
Mariposa rush is a California native perennial found in the Klamath Ranges, northern Sierra Nevada, Sacramento Valley, San Francisco Bay Area, southern Coast Ranges, Santa Barbara, Peninsular Ranges, and eastern Mojave Desert in wet places at elevations below 2,000 meters. Growing densely matted with stout rhizomes, this rush forms stems 15 to 70 centimeters tall with few cauline leaves and prominent scarious sheath appendages 4 to 6 millimeters long. Its cylindric leaves have complete crosswalls, creating a distinctive growth pattern. The plant produces flower clusters with 4 to 10 flowers, where perianth parts are approximately 2.5 to 3 millimeters long and bristle-tipped. Its fruit is slightly longer than the perianth and three-sided, with tiny obovate seeds featuring minute appendages.
Identification and appearance
Key characters: 62 sympatric species; key features are dense mats, prominent scarious appendages, and complete crosswalls
Habitat and range
Habitat: Wet places
Elevation: < 2000 m
California counties: San Bernardino, San Diego, Butte, Mono, Orange, Tulare, Alameda, Lassen, Marin, Mariposa, Nevada, Placer, Sierra, Siskiyou, Sonoma, Inyo, Los Angeles, Riverside, Monterey, San Luis Obispo, Madera, Lake, Kern, Tehama, Shasta, Yuba, Plumas, Tuolumne, Merced, Fresno, Napa, Del Norte, Mendocino, Santa Barbara, Ventura
Outside California: northern Mexico
How to tell it apart
vs Schoenoplectus: Juncus has leaf blades present; Schoenoplectus is leafless with only bladeless sheaths at base.; vs Carex: Juncus has round or flattened stems; Carex has triangular stems you can feel.; vs Luzula: Run finger along leaf edge - smooth = Juncus, hairy = Luzula.; vs Elegia: Juncus has small individual flowers; Elegia has showy papery bracts and branching structure.; vs Cyperus: Juncus has round stems and capsules; Cyperus has triangular stems and lens-shaped achenes.
Frequently asked questions
Is Juncus dubius native to California?
Yes. Juncus dubius is native to California (recorded as native).
Where in California does Juncus dubius grow?
Juncus dubius occurs in San Bernardino, San Diego, Butte, Mono, Orange, Tulare, Alameda, Lassen and other counties, at elevations of < 2000 m.
What plant family does Juncus dubius belong to?
Juncus dubius is in the Juncaceae family, genus Juncus.
What habitat does Juncus dubius grow in?
Juncus dubius grows in Wet places.
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.