Skeletonleaf bursage Ambrosia tomentosa Nutt.

Asteraceae — (Sunflower family)

Skeletonleaf bursage is a perennial 4 to 18 inches tall with extensive creeping rootstocks. Stems are branched and somewhat spreading; leaves 2 to 5 inches long alternate, ovate to lanceolate in outline, coarsely toothed and deeply segmented with the lower surface covered with minute white hairs. The upper surface is smooth and green. Flowers are inconspicuous and yellow. Staminate flowers are found in solitary, elongated, terminal clusters; pistallate flowers form in pairs in leaf axils below. Fruit is a light brown bur with conical spines and contains one or more achenes.

This weed is native of the plains region. It grows in cultivated fields, pastures, prairies and waste areas. It also survives well under varied soil moisture conditions. Skeletonleaf bursage is a difficult weed to control because of its extensive horizontal root system. Flowering and seed production occur from late June to August.
(Courtesy of Weeds of the West)