Erigeron sumatrensis

Tropical horseweed

Family: Asteraceae · Type: annual · Not Native

Tropical horseweed is a naturalized annual plant found in northwestern California, the northern Sierra Nevada foothills, Sacramento Valley, central western California, southern California coastal areas, Channel Islands, and Peninsular Ranges at elevations below 600 meters in disturbed sites. Flowering throughout the year, this plant produces white or cream flowers in small heads arranged in panicle-like clusters. Growing with erect, leafy stems 30 to 200 centimeters tall, it branches extensively and has stems covered in fine, ascending hairs with the central stem typically taller than its branches. Its leaves range from linear to elliptic or oblanceolate, with basal and lower stem leaves 5 to 10 centimeters long and 5 to 20 millimeters wide, often withering by flowering time. The fruit is pale tan, sometimes with reddish ribs, and measures 1 to 1.5 millimeters long with 15 to 25 cream to tan pappus bristles.

Habitat: Disturbed sites

Bloom period: All year

Elevation: < 600+ m

Bioregions: NW (exc NCoRH), CaRF, n SNF, ScV, CW (exc SCoRI), SCo, ChI, PR (exc SnJt)

California counties: Los Angeles, Monterey, San Bernardino, San Diego, Santa Barbara, Sonoma, Ventura, Orange, Riverside, El Dorado, Alameda, Santa Cruz, San Luis Obispo, Butte, Sutter, Glenn, Yuba, Colusa, Napa, San Mateo, Sacramento, San Francisco, Yolo, San Joaquin, Stanislaus, Placer, Merced

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Jepson eFlora, Cal-IPC, and more.