Ambrosia trifida

Giant ragweed

Family: Asteraceae · Type: annual · Not Native

Conservation status: Cal-IPC Yes

Giant ragweed is a naturalized annual found in northern San Joaquin Valley, central and western California, and southwestern and Mojave Plateau regions in dry, disturbed places at elevations below 800 meters. Flowering from June to September, this plant produces small greenish flower heads in dense clusters. Growing up to 2 meters tall with thick, fleshy stems that are soft-hairy and black-lined, it develops a slightly woody base. Its opposite leaves are large, often 6 to 35 centimeters long, with distinctive palmately lobed blades that are lanceolate to widely ovate and deeply serrated. The plant produces unusual bur-like fruits 6 to 12 millimeters long with 4 to 8 short spines arranged in a ring around the fruit's tip.

Habitat: Dry, disturbed places

Bloom period: Jun-Sep

Elevation: < 800 m

Bioregions: n SnJV, CW, SW, MP

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