Bigelow’s false thoroughwort

Eupatorium bigelovii A. Gray in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 75. 1859; E. madrense S. Watson

Shrubs, 50–150 cm. Stems erect, sparsely puberulent. Petioles 1–4 mm. Leaf blades deltate to deltate-lanceolate or ovate-lanceolate, 3–7 × 1–4 cm, margins serrate to dentate (abaxial faces reticulate-veiny with raised whitish, secondary veins, minutely gland-dotted). Heads usually in 3s, sometimes borne singly. Peduncles 0 or 2–8(–12) mm. Involucres turbinate to campanulate, 5–7 mm. Phyllaries in 4–5 series, apices of the inner appressed, acute (not petaloid or expanded). Corollas pale blue or white.

Flowering Oct–Dec. Dry limestone hills in oak woodlands, talus; 1000–1800 m; Tex.; Mexico (Coahuila, Nuevo León, San Luis Potosí).