Xanthium spinosum
Spiny cocklebur, spiny clotbur
(c) Bruce Calvert, some rights reserved (CC BY), uploaded by Bruce Calvert · licence
Family: Asteraceae · Type: Herb · Native
Xanthium spinosum (Spiny cocklebur) is a native California herb in the Asteraceae family.
Spiny cocklebur is a naturalized annual found in the California Floristic Province in disturbed, seasonally wet sites including grasslands, marshes, and watercourses at elevations below 1,875 meters. Flowering from July to October, this plant produces small, inconspicuous flowers in heads without an involucre. Growing with minutely strigose stems 10 to 60 centimeters tall, occasionally reaching up to 120 centimeters in height, it spreads across disturbed landscapes with a weedy growth habit. Its leaves are pinnately veined and often pinnately 3-lobed, with blades 4 to 8 centimeters long and 1 to 3 centimeters wide, featuring entire or slightly toothed margins. The plant produces distinctive spiny burs 10 to 12 millimeters long that easily attach to clothing and animal fur.
Identification and appearance
Key characters: 1 sympatric species. Key differentiator is pinnately vs palmately veined leaves and leaf margin differences.
Habitat and range
Habitat: Disturbed, seasonally wet, often alkaline sites, in grassland, marshes, watercourses
Elevation: < 1875 m
Outside California: worldwide, probably native to South America
Bloom period
Xanthium spinosum blooms Jul-Oct.
How to tell it apart
vs Ambrosia: Cockleburs are closest to ragweeds and bursages, both being monoecious with inconspicuous petal-less heads, but Ambrosia burs are small with a single seed and one ring of short spines, while Xanthium burs are large (1-3 cm), two-seeded, densely hook-prickled, and tipped by a pair of beaks.; vs Arctium: Burdock burs also cling by hooked spines, but a burdock bur is a whole flower head of many purple disk florets ringed by hooked phyllaries, whereas the Xanthium bur is a hard, woody, two-chambered case.; vs Amaranthus: Spiny amaranth shares the paired sharp spines at leaf nodes seen in spiny cocklebur, but amaranth bears tiny green flower clusters and never forms a bur.; vs Datura: Thorn-apple also has a spiny fruit, but it is a broad-leaved forb with large white trumpet flowers and a spiny capsule that splits open, not a composite bur.; vs Cirsium: Thistles are spiny weeds too, but they carry showy pink to purple flower heads with plumed pappus, unlike cocklebur's drab, inconspicuous heads and beaked prickly bur.
Frequently asked questions
Is Xanthium spinosum native to California?
Yes. Xanthium spinosum is native to California (recorded as native).
When does Xanthium spinosum bloom?
Xanthium spinosum blooms Jul-Oct.
What plant family does Xanthium spinosum belong to?
Xanthium spinosum is in the Asteraceae family, genus Xanthium.
What habitat does Xanthium spinosum grow in?
Xanthium spinosum grows in Disturbed, seasonally wet, often alkaline sites, in grassland, marshes, watercourses.
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.