Salvinia molesta
Kariba weed
(c) Will McFarland, some rights reserved (CC BY), uploaded by Will McFarland · licence
Family: Salviniaceae · Type: Herb · Not Native
Conservation status: Cal-IPC Yes
Salvinia molesta (Kariba weed) is a non-native California herb in the Salviniaceae family, recognized by leaf size and joined hair tips forming dark knots.
Kariba weed is a naturalized fern found in southern California and the Colorado River region in river channels, backwaters, and floodplain ponds at elevations generally below 100 meters. This invasive aquatic fern has distinctive floating leaves approximately 15 to 25 millimeters wide, nearly round and spreading across water surfaces. Growing as a floating plant with delicate, intricate leaf structures, it spreads quickly across water environments. Its leaves feature unique papillae on the upper surface, with tiny hairs that form dark knots at their tips, creating a distinctive textural appearance. When established, this aggressive species can rapidly colonize and cover water surfaces, forming dense floating mats.
Identification and appearance
Key characters: 2 sympatric species; distinguished by leaf size and joined hair tips forming dark knots
Habitat and range
Habitat: River channels, backwaters, floodplain ponds
Elevation: generally < 100 m
California counties: Imperial, Orange, San Diego, San Luis Obispo, Riverside, Mendocino
Outside California: +- worldwide in tropics; native to Brazil.
Conservation status
Cal-IPC Yes
How to tell it apart
vs Azolla: Azolla has pinhead-sized leaves under 2 mm; Salvinia has fingernail-sized leaves 5-25 mm.; vs Eichhornia: Eichhornia has inflated spongy leaf stalks; Salvinia has flat fuzzy leaves.; vs Pistia: Pistia forms circular rosettes with clear veins; Salvinia has paired fuzzy leaves along stems.
Frequently asked questions
Is Salvinia molesta native to California?
No. Salvinia molesta is not native to California (recorded as not native).
Where in California does Salvinia molesta grow?
Salvinia molesta occurs in Imperial, Orange, San Diego, San Luis Obispo, Riverside, Mendocino, at elevations of generally < 100 m.
What plant family does Salvinia molesta belong to?
Salvinia molesta is in the Salviniaceae family, genus Salvinia.
Is Salvinia molesta invasive in California?
Salvinia molesta is listed by Cal-IPC with an invasiveness rating of Yes.
What habitat does Salvinia molesta grow in?
Salvinia molesta grows in River channels, backwaters, floodplain ponds.
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.