Euphorbia helioscopia
Wartweed, Wartweed
(c) portioid, some rights reserved (CC BY), uploaded by portioid · licence
Family: Euphorbiaceae · Type: Herb · Not Native
Euphorbia helioscopia (Wartweed) is a non-native California herb in the Euphorbiaceae family, recognized by 5-whorled leaves and no appendages diagnostic.
Wartweed is a naturalized annual found in northern California Coast Ranges, San Francisco Bay Area, Central Coast, and Southern California coastal areas in disturbed areas at elevations below 200 meters. Flowering from April to July, this plant produces small, green-tinged flowers in complex clustered cyathia. Growing with erect stems 10 to 50 centimeters tall that are glabrous or sparsely hairy, it develops distinctive whorled leaves near the top of the plant. Its leaves are obovate to spoon-shaped, measuring 1 to 3 centimeters long, with finely toothed edges and a rounded or notched tip. The fruit is a smooth, spherical, lobed structure approximately 2.5 to 3 millimeters wide, containing flattened ovoid seeds with a delicate net-like surface.
Identification and appearance
Key characters: 20 sympatric species; 5-whorled leaves and no appendages diagnostic
Habitat and range
Habitat: Disturbed areas
Elevation: < 200 m
California counties: San Francisco, San Mateo, Los Angeles, San Luis Obispo, Humboldt, Inyo, Contra Costa, Santa Cruz, San Diego, Yolo
Outside California: native to Europe
Bloom period
Euphorbia helioscopia blooms Apr-Jul.
How to tell it apart
vs Croton: Euphorbia bleeds milky white latex and packs its flowers into a tiny cup (cyathium) rimmed with nectar glands; Croton has watery sap, stellate or scaly hairs, and ordinary small separate male and female flowers.; vs Stillingia: Euphorbia flowers sit in a gland-bearing cyathium; Stillingia bears its flowers in a spike with a pair of glands flanking each subtending bract and has no cyathium cup.; vs Ditaxis: Euphorbia has latex and the cyathium; Ditaxis has clear sap, 5-parted petaled male and female flowers, and 2-forked (malpighiaceous) hairs.; vs Asclepias: Both ooze milky sap, but Euphorbia's minute flowers cluster in a cyathium and ripen into a 3-lobed capsule; milkweeds have showy 5-parted flowers with a crown and paired follicles of plumed seeds.; vs Polygonum: Prostrate mat spurges leak milky sap when torn and have paired stipules with opposite leaves at the nodes; knotweeds have clear sap and a papery sheath (ocrea) wrapping each node.
Frequently asked questions
Is Euphorbia helioscopia native to California?
No. Euphorbia helioscopia is not native to California (recorded as not native).
When does Euphorbia helioscopia bloom?
Euphorbia helioscopia blooms Apr-Jul.
Where in California does Euphorbia helioscopia grow?
Euphorbia helioscopia occurs in San Francisco, San Mateo, Los Angeles, San Luis Obispo, Humboldt, Inyo, Contra Costa, Santa Cruz and other counties, at elevations of < 200 m.
What plant family does Euphorbia helioscopia belong to?
Euphorbia helioscopia is in the Euphorbiaceae family, genus Euphorbia.
What habitat does Euphorbia helioscopia grow in?
Euphorbia helioscopia grows in Disturbed areas.
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.