Triligulate bristlecup sandmat Triligulate bristlecup sandmat

Euphorbia fendleri Torrey & A. Gray var. triligulata L. C. Wheeler, Bull. Torrey Bot. Club 63: 445. 1936; Chamaesyce chaetocalyx (Boissier) Wooton & Standley var. triligulata (L. C. Wheeler) Mayfield

Leaf blades narrowly-ovate to linear-lanceolate, 3–11 × 0.8–3 mm. Involucral gland appendages straplike, divided into 3–5 linear segments, each 0.8–1.1 × 0.1 mm.

Flowering and fruiting early summer–fall. Canyon walls, crevices in boulders; of conservation concern; 600–900 m; Tex.; Mexico (Coahuila).

Variety triligulata was described from the cliffs of Boquillas Canyon, on both sides of the Rio Grande in Texas and adjacent Coahuila, Mexico. The variety has elongate involucral gland appendages that are divided into three to five linear, straplike segments; it appears to represent a distinctive, localized population within the overall distribution of Euphorbia chaetocalyx. More generally, populations of E. chaetocalyx from elsewhere in northern Coahuila, Mexico, have similarly shaped involucral gland appendages and may represent additional populations of var. triligulata.