Tribulus terrestris L.
CC = *
CW = 5
MOC = 36
Family - Zygophyllaceae
Stem - To 1 m, prostrate, pubescent with minute curled hairs and longer stiff hairs.
Leaves - Opposite, even-pinnately compound, with one leaf at a node usually distinctly larger than the other. Leaves to 5 cm long, elliptic in outline, with 6-8 pairs of leaflets, these densely pubescent on undersurface and margin, the upper surface pubescent, sometimes only along midvein.
Calyx - Sepals 5, free, 2-4 mm long, densely pubescent.
Flowers - Corollas of 5 free petals, yellow, sometimes fading to white. Stamens 10, in 2 series opposite the sepals and petals. Ovary 1 per flower, superior, of 5 fused carpels, with 5 or 10 locules. Style and stigma 1 per flower. Ovules 1 or few per locule.
Fruit - Schizocarps, 7-12 mm in diameter, depressed globose, strongly 5-lobed, each mericarp with two stout, sharp spines.
Flowering - June - September.
Habitat - Open, disturbed areas. Prefers sandy soils.
Origin - Native to Mediterranean region.
Other info. - A caltrop is an device which, when tossed upon the ground, will always orient a sharp spine upward. They have been used as antipersonnel devices and to puncture tires of fleeing vehicles. Although the fruits of this plant may not operate precisely in that manner, they do have a reputation for puncturing bicycle tires. Some of the above photos were taken at a trailhead for the Katy biking trail!
Photographs taken near Treloar, Warren County, MO, 6-20-2012, at Dresser Island Conservation Area, St. Charles County, MO, 8-13-2012, and at Rose Pond Conservation Area, Clark County, MO, 7-9-2017 (SRTurner).