Annual herb forming mats to 1 m wide Stem: prostrate, branched from the base, and hairy. Leaves: opposite, pinnately compound, short-stalked, 2 - 6 cm long. Leaflets usually in pairs of six to eight, 0.5 - 1.5 cm long, oblong. Flowers: solitary, in axils, on 0.5 - 1 cm long stalks, yellow, to 1 cm wide. Sepals awl-shaped. Ovary five-chambered. Stamens two to three times as many as petals. Fruit: dry, indehiscent, splitting into five segments, to 1 cm wide, spiny, with tuber-like projections. Each segment divided into three to five one-seeded compartments.
Similar species: No information at this time.
Flowering: mid-June to late September
Habitat and ecology: Introduced from Europe. Local along unpaved roads and streets, and in the parking lots of towns with sandy soil. It has also been found along railroads and in sandy cultivated fields.
Occurence in the Chicago region: non-native
Etymology: Tribulus is the Latin name for a caltrop, referring to the spiny fruit of this plant. Terrestris means terrestrial.
Author: The Morton Arboretum
Wiggins 1964, Kearney and Peebles 1969, USDA GRIN
Duration: Annual Nativity: Non-Native Lifeform: Forb/Herb General: Mat-forming, prostrate annual herb with diffusely branching stems 10-80 cm long; herbage sparsely silky-strigose throughout, though upper leaflet surfaces can be nearly glabrous. Leaves: Opposite, even-pinnate, 2-5 cm long, with 3-9 pairs of elliptic or oblong leaflets 3-13 mm long; one of each pair of leaves smaller or abortive; leaflets oblique (having an asymmetrical base), acute to obtuse at apex; lowest pair of leaflets unequal in size; stipules subulate, 2-3 mm long. Flowers: Solitary in axils of smaller or abortive leaves, pedicel shorter than the subtending leaf; sepals 5, narrowly lance-ovate, 3 mm long, caducous; petals 5, pale yellow, 4-5 mm long; stamens 10, in 2 whorls, the outer whorl adnate to petals; ovary hirsute, with 5 locules. Fruits: Capsule, 2 cm wide, breaking into 5 spiny nutlets, each with 2 larger spines; after separation the vicious tacklike nutlets land with the larger spines upward. Ecology: Found in cultivated areas, along roads, disturbed sites; below 8,000 ft (2438 m); flowers July-October. Distribution: Exact native range obscure, probably native to Asia, Africa, and s. and e. Europe; naturalized throughout the world; N. Amer., in every state in the U.S. except Al, GA, and WV; also in B.C. and Ontario; south to S. Amer. Notes: Highly distinct and identified by walking barefoot where it occurs, the intense sting and subsequent expletives are a dead give-away. The ubiquitous -goatheads- are the woody, hardened fruits of this plant and their sharp projections. The plant is also distinct by the tightly ground-hugging prostrate habit, pinnately compound leaves, and yellow flowers. Growth form and flowers are similar to Kallstroemia spp. but that genus has non-spiny fruits topped with a single persistent style (a -beak-). Ethnobotany: Used as medicine by cultures around the world, including modern use as an herbal dietary supplement to enhance athletic ability. Etymology: Tribulus is Latin for three-pointed, a caltrop, while terrestris in Latin means on land. Synonyms: None Editor: SBuckley 2010, FSCoburn 2015, AHazelton 2015
Annual; stems hirsute, branched from the base, forming mats to 1 m wide; lvs short-petioled, 2-6 cm, one of each pair distinctly the larger; lfls usually 6-8 pairs, oblong, 5-15 mm; peduncles 5-10 mm; fls 8-10 mm wide; intrastaminal glands distinct, not forming a ring; body of the fr 1 cm thick, each segment with 2 stout divergent spines and a longitudinal row of tubercles; 2n=12, 24, 26, 48. Native of the Mediterranean region, well established as a roadside weed in w. U.S., and occasionally found in our range.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.