Thymophylla Tephroleuca, commonly known as the ashy dogweed or ashy prickly-leaf, is an exceptionally rare, federally endangered perennial subshrub endemic to the semi-arid thornscrub communities of the Rio Grande Plain in deep South Texas. This low-growing, highly branched woody plant typically forms dense, rounded clumps standing 10 to 30 cm (4 to 12 inches) tall from a sturdy taproot. The entire plant—including its stiff, erect stems and foliage—is covered in a thick, velvety layer of soft, appressed, and woolly white hairs (tomentum). This dense pubescence gives the plant a striking, distinctively ashy-gray or silvery appearance and serves as a vital adaptation to reflect intense desert sunlight and conserve moisture. Its alternate, gray-green leaves are linear to narrowly oblanceolate, measuring 5 to 15 mm long and 1 to 3 mm wide, with entire or occasionally 3-lobed margins that are often tipped with a tiny, sharp point. The leaf blades also feature small, inconspicuous, embedded oil glands that emit a strong, pungent, characteristic dogweed odor when crushed.

The species exhibits a sporadic blooming cycle, producing small, daisy-like flower heads primarily from spring through fall, often triggered directly by localized rainfall events. The terminal flower heads are borne solitary on slender, woolly peduncles up to 2 cm long and are surrounded by a cup-like involucre composed of fused, glandular bracts. Each head features 8 to 14 bright yellow ray florets surrounding a central disc of 25 to 40 fertile, yellow tubular florets, creating a vibrant contrast against the silvery foliage. Following pollination, the flowers develop into small, dark brown to black, narrowly obconic achenes (cypselae) that are 2 to 3 mm long and capped by a pappus of short scales to aid in localized dispersal. Strongly restricted to calcareous sandy loams, shallow clay loams, and caliche outcrops within Texas ebony, kramería, and guajillo-dominated thornscrub, Thymophylla tephroleuca is globally confined to just a few isolated populations within Zapata and Starr counties, Texas. It faces severe, ongoing threats from broad-scale brush clearing, highway expansion, and the encroachment of invasive buffelgrass.