Parthenium argentatum

Shrubs, 30-100+ cm. Leaf blades lanceolate to oblanceolate, 15-25(-40+) × 6-15(-25+) mm, margins mostly entire, some with 1-2(-5) sharp teeth, faces densely strigillose (gray to white) and obscurely or not at all gland-dotted. Heads radiate, in glomerules of 3-5+ at ends of ± ebracteate stalks 8-15(-20+) cm. Peduncles 1-2(-6+) mm. Phyllaries: outer 5 oval-elliptic, 2.5-3+ mm, inner 5 ± orbiculate, 3.5-4 mm. Pistillate florets 5; corolla laminae ovate, 1.2-1.5 mm. Disc florets 20-30+. Cypselae ± obovoid, 2.5-3 mm; pappus-like enations 2(-4), erect to spreading, ± subulate, 0.3-0.8 mm. 2n = 36.

Flowering Apr-Jun. Calcareous soils; 1000-1500 m; Tex.; Mexico.

Guayule has sometimes been used for commercial production of natural rubber. Hybrids between Parthenium argentatum and P. incanum have been noted.