- Xanthium spinosum is an erect, rigid, much-branched annual herb, 11.8-39.4 in. (30-100 cm) tall and up to 59.1 in. (150 cm) or more wide. Stems are striate, yellowish or brownish gray, and finely pubescent.
- Leaves are lanceolate, entire, toothed or lobed, 1.2-3.1 in. (3-8 cm) long, 0.24-1.02 in. (6-26 mm) wide, glabrous or strigose above, and silvery-tomentulose beneath. They are dull gray-green above with a conspicuous white midrib and short petioles 0.4 in. (1 cm). Each leaf base is armed at the axil with yellow three-pronged spines 0.8-2 in. (2-5 cm) long, often opposite in pairs.
- The monoecious flowers may be solitary or found in axillary clusters. Greenish flowers are inconspicuous.
- Fruits are yellowish egg shaped burs covered with hooked glabrous spines. Each fruit contains two seeds.
- Ecological Threat
- Xanthium spinosum is a serious weed in many agricultural crops and in animal production. Seeds are easily spread, due to their ability to float and to "hitchhike" on humans and animals. The plants can quickly become dominant in an area due to prolific seed production and high germination and survival rates. It invades pastures and grazing lands, reducing forage production. Xanthium species are toxic to most domestic animals, particularly swine and horses.
The following description of Xanthium spinosum is adapted from Abrams (1940), Jepson (1951), Munz and Keck (1973), Robbins et al. (1970), and Holm et al. (1977).
Xanthium spinosum is an erect, rigid, much-branched annual herb, 3-10 dm tall and up to 15 dm or more wide. Stems are striate, yellowish or brownish gray, and finely pubescent. The cotyledons are linear-lanceolate in shape, differing in appearance from later developing leaves. True leaves are lanceolate, entire, toothed or lobed, 3-8 cm long, 6-26 mm wide, glabrous or strigose above, and silvery-tomentulose beneath. They are dull gray-green above with a conspicuous white midrib and short petioles (1 cm). Each leaf base is armed at the axil with yellow three-pronged spines 2-5 cm long, often opposite in pairs.
Flower heads are in axillary clusters or often solitary. Flowers are inconspicuous, greenish, and monoecious; male flowers in almost globular heads in axils of upper most leaves, and female flowers in axils of lower leaves, developing into a bur. The bur is two--celled, oblong, nearly egg-shaped, slightly flattened, 10-13 mm long, 4 mm wide, pale yellowish, more or less striate, glandular, covered with slender, hooked, glabrous spines from more or less thickened bases, with the two apical beaks short and straight. Each bur contains two flattened, thick-coated, dark brown or black seeds, the lower germinating first.
Xanthium is derived from the Greek, xanthos, meaning "yellow" and is thought to refer to a yellow dye obtainable from some species.
Unlike cocklebur (X. strumarium), spiny clotbur has conspicuous narrower leaves tapering at both ends, short petioles, conspicuous three-pronged spines at the leaf base, and egg-shaped burs covered with hooked, thorny prickles.
- Element Stewardship Abstract - The Nature Conservancy
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EDDMapS Distribution - This map is incomplete and is based only on current site and county level reports made by experts, herbaria, and literature. For more information, visit www.eddmaps.org
State Invasive List - This map identifies those states that list this species on their invasive species list. For more information, visit Invasive.org
Invasive Listing Sources
|Common Name Reference:|| Weed Science Society of America Common Names List|
|Scientific Name Reference:||USDA, NRCS. 2010. The PLANTS Database. National Plant Data Center, Baton Rouge, LA, USA.|