Puncturevine, from the Zygophyllaceae or (Caltrop family) and sometimes better known as a goathead, is a plant designed to survive. From the time the seed sprouts until it blooms and starts to form seed can vary, but usually only takes 2 - 3 weeks. The plant will continue to grow and produce seed until it is stopped. The first freeze will kill the plant in the fall. This adventive annual plant develops a mat of prostrate stems about 1-3' across; it branches frequently at the base, and occasionally elsewhere. The round stems are initially green, but quickly become brown; they are densely covered with short hairs and sparsely covered with long hairs. The compound leaves are evenly pinnate, consisting of 4-8 pairs of leaflets. Each compound leaf is about 2-4" in length, and it has a hairy central stalk. The dark green leaflets are up to ¾" long and ¼" across; they are, oblong, smooth along the margins, and sparsely to moderately hairy. There is a short petiole at the base of each leaflet. The flowers occur individually from the axils of the compound leaves on hairy pedicels about ½–¾" long. Each flower is about ½" across, consisting of 5 yellow petals, 5 triangular green sepals, 10 stamens with yellow anthers, and a pistil with a 5-lobed stigma. The petals are well-rounded and longer than the sepals. Puncture Vine is typically found at dry sunny sites with scant vegetation; the soil usually contains an abundance of sand or gravel. It forms root nodules with rhizobial bacteria and adds nitrogen to the soil.
Sources: Puncturevine - Idaho Weed Awareness, http://www.idahoweedawareness.net/vfg/weedlist/puncturevine/puncturevine.html (accessed January 20, 2017). Tribulus terrestris - Details - Encyclopedia of Life, http://eol.org/pages/581147/details (accessed January 20, 2017). Puncture Vine (Tribulus terrestris) - Illinois Wildflowers, http://www.illinoiswildflowers.info/weeds/plants/puncture_vine.htm (accessed January 20, 2017).