Some of the worst invasive ornamental plants, where they're found in California and their ecological damage rating

Giant reed, Arundo
Found in: Riparian areas; central west, great valley, northwest, Sierra Nevada, southwest, Sonoran and Mojave deserts.
Ecological damage rating: High

Fountain  grass
Found in: Coastal dunes and scrub, chaparral, grasslands; central west, great valley, southwest, Mojave and Sonoran deserts.
Ecological damage  rating: Moderate

Scotch broom
Found in: Coastal scrub, oak woodland; Cascade Range, central west, great valley, northwest, Sierra Nevada, southwest
Ecological damage  rating: High

French broom
Found in: Coastal scrub, oak woodland, grasslands; Cascade Range, central west, northwest, Sierra Nevada, southwest
Ecological damage  rating: High

Spanish broom
Found in: Coastal scrub, grasslands, wetlands, oak woodland, forests; Cascade Range, central west, great valley, northwest, Sierra Nevada, southwest, Mojave Desert
Ecological damage  rating: High

Periwinkle
Found in: Riparian, oak woodlands, coastal scrub; Cascade Range, central west, great valley, northwest, Sierra Nevada, southwest, Mojave Desert
Ecological damage  rating: Moderate

Saltcedar, tamarisk
Found in: Desert washes, riparian areas, seeps and springs; central west, Great valley, northwest, Sierra Nevada, eastern Sierra Nevada, southwest, Mojave and Sonoran deserts
Ecological damage  rating: High

Blue gum eucalyptus

Found in: Riparian areas, coastal grasslands, scrub; Central west, great valley, northwest, southwest
Ecological damage  rating: Moderate

Chinese tallow tree
Found in: Riparian areas; Central west, great valley, northwest
Ecological damage  rating: Moderate

Pampas grass
Found in: Coastal dunes, coastal scrub, Monterey pine, riparian, grasslands, wetlands, serpentine soils; Cascades Range, central west, northwest, Sierra Nevada, southwest, Mojave Desert
Ecological damage  rating: High

Russian olive
Found in: Interior  riparian;  Central west, great valley, southwest, eastern Sierra Nevada, Mojave desert
Ecological damage  rating:  Moderate

Red sesbania,  scarlet wisteria
Found in: Riparian areas; Cascade Range, central west, great valley, northwest, Sierra Nevada, southwest,  Sonoran Desert
Ecological damage  rating: High

Capeweed
Found in: Coastal prairie; Central west, northwest
Ecological damage  rating: Moderate

Hottentot-fig, iceplant
Found in: Coastal  habitats, especially dunes; central west, northwest, southwest.
Ecological damage  rating: High

Myoporum

Found in: Coastal habitats, riparian areas; central west, southwest
Ecological damage  rating: Moderate