Plants straggling, very tall and slender, sparingly branched at any level. Stems initially erect, later sprawling or clambering, long cylindric, 12-60(-130) × 0.6-1(-2) cm; ribs 8-10, crests low, uninterrupted or shallowly undulate; areoles 1-2-5 mm apart. Spines (9-)11-13(-17) per areole, stiff and straight, usually tan, brown, or black, sometimes yellow, pale pink, ashy white, or gray, sometimes black central spines contrasting with white radial spines; radial spines 8-16 per areole, 2-5 mm; central spines 1(-3) per areole, closely appressed (except at the stem tip), terete, 4-9 mm. Flowers 3.5-6 × 3.5-7 cm; flower tube 15-20 × 7-18 mm; flower tube hairs 3-5(-10) mm; inner tepals rose-pink with darker pink to magenta midstripes, proximally darker, 25-35 × 4-12 mm, tips relatively thin and delicate; anthers yellow; nectar chamber 1-4 mm. Fruits dark green to brownish, 2-3 cm, pulp white. 2n = 22.

Flowering Mar-Apr; fruiting 2.5-3 months after flowering. Tamaulipan thorn scrub, alluvial soils; 0-200[-1100] m; Tex.; Mexico (Coahuila, Nuevo León, Tamaulipas).

Echinocereus poselgeri, with tuberous roots and erect, slender, elongate stems, superficially resembles some Peniocereus species. The polyphyletic genus Wilcoxia Britton & Rose formerly included this species along with species of Peniocereus. The flowers, fruits, and seeds of E. poselgeri are typical for Echinocereus, quite similar to those of E. reichenbachii.