An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
BUFFALOBUR, Colorado bur, Mexican thistle, Texas thistle
BUFFALOBUR-Solanum rostratum Dunal
DESCRIPTION-A low yellow, spired, vicious soft hairy annual which reproduces by seeds. The stems, mostly branching in the upper part, are erect and bushy, 1/2 to 2 feet long. The entire plant, except the petals, is covered by straight yellow spines, 1/8 to 1/2 inch long. The leaves are alternate, 2 to 6 inches long including the stalks, irregularly cut into 5 to 7 lobes, and often these are 2- to 5-lobed. They are covered by short yellow starlike hairs, and the midribs, veins, and leaf stalks are spiny.
The yellow flowers are 5-lobed, wheelshaped, 1 to 1 1/2 inches across, in few flowered clusters on spiny flower stalks. The calyx is covered by spines. It enlarges and forms a spiny bur, enclosing and completely covering the seedpod. The seeds are almost circular, 1/2 inch or slightly more in diameter, brown to reddish brown, flattened, irregularly angled, with a finely pitted surface.
DISTRIBUTION-Buffalobur, native in the Great Plains region, was probably introduced into Arizona. It grows on dry hard soil to rich moist soil of cultivated lands, as in the cotton fields of Safford (Graham County) or Avra (Pima County) valleys. Abundant throughout northern and central Arizona and increasing southward along roadsides, yards, waste places, and overgrazed plains, sometimes covering areas many miles in extent, as south of Prescott around Mayer (Yavapai County). It is obnoxious on farms or rangelands; 1,000 to 7,000 feet elevation; flowering June to September.
POISONOUS PROPERTIES-The leaves and seedpods of buffalobur contain the poisonous alkaloid solanine.
Copyright (c) 1972 The Arizona Board of Regents