An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
PUNCTUREVINE, bullhead, goathead
PUNCTUREVINE-Tribulus terrestris L.
DESCRIPTION-A restricted noxious weed in Arizona, puncturevine is a prostrate silky hairy annual from a shallow taproot, reproducing only by seeds. The trailing stems, 1 to 5 (or to 8 ) feet long, branching and radiating from the root, often form dense mats several feet in diameter. Or the stems may be nearly erect where growing in competition for light. The leaves are opposite, divided into 4 to 7 pairs of oblong leaflets 1/8 to 1/2 inch long.
The bright yellow flowers, with 5 petals which are open only in the mornings, are solitary on short stalks in the axils of the leaves. The seedpod consists of a cluster of 5 flat spiny burs or nutlets, which break apart at maturity. Each nutlet or bur contains 2 to 5 seeds, and has 2 vicious spines on its back. Most of the burs are turned so they lie under the plant. The seeds may remain viable for many years until there is sufficient moisture for germination.
DISTRIBUTION-Puncturevine is native in Europe. It is abundant, one of the most obnoxious weeds in southern Arizona, and is found throughout the state. It is especially troublesome in lawns, citrus orchards, sorghum, alfalfa, cotton, small grain, pastures, gardens, roadsides, yards, and walks; up to 7,000 feet, but mostly at lower elevations; flowering March to October, but principally in July and August.
It appears in remarkable numbers soon after the start of the summer rains on any type of barren soil along the city streets and yards of southern Arizona. In wet summers it is often covered by dodder (Cuscuta sp.). Each plant produces innumerable burs, and it is almost impossible to prevent their falling on the ground once they are mature. Home owners and their dogs probably dislike puncturevine more than any other weed because the stout spines can easily penetrate shoes, bicycle tires, and dogs' feet.
Copyright (c) 1972 The Arizona Board of Regents