Plants perennial, glabrous, with vertical rootstock. Stems ascending or decumbent, usually producing axillary shoots below 1st-order inflorescence or at proximal nodes, 40-70 cm. Leaf blades lanceolate or broadly lanceolate, 5-10(-15) × 2-3(-4) cm, usually ca. 3-4 times as long as wide, widest in proximal 1/2, rarely near middle, thick, often subcoriaceous, base cuneate, margins entire, flat, apex acute or attenuate. Inflorescences terminal and axillary, terminal usually occupying distal 1/ 1/ 3 of stem, rather dense or interrupted in proximal 1/ 2, usually narrowly paniculate (branches simple and comparatively short). Pedicels articulated in proximal 2 almost near base, thickish, 3-6(-7) mm, usually approximately as long as or slightly shorter than inner tepals, articulation indistinctly swollen. Flowers 12-20 in whorls; inner tepals ovate or cordate-triangular, occasionally almost orbiculate, 5-6 × 4-5 mm, base truncate or indistinctly cordate, margins entire, apex obtuse or subacute; tubercles absent or 1 inner tepal with indistinctly swollen midvein. Achenes brown, 2.7-3.2 × 1.8-2.5 mm. 2n = 20.

Flowering spring-early summer. Sandy, gravelly, and muddy shores of rivers and streams; 10-1000 m; Ariz., N.Mex., Tex.

Rumex ellipticus is closely related to R. altissimus and is sometimes regarded as a subspecies of it (Á. Löve 1986).