Plants perennial, distinctly and often densely tomentose and/or papillose-pubescent, especially ab-axial sides of leaf blades, ocreae, and petioles, with fusiform, ver-tical rootstock. Stems erect, branched in distal 1/ 2/ 3, 30-70(-100) cm. Leaves: ocrea deciduous or partially persistent at maturity; blade oblong-lanceolate, 20-30 × 5-10 cm, base cordate to broadly cuneate, margins entire, repand, flat or crisped, apex acute or attenuate. Inflorescences terminal, occupying distal 1/ 2/ 3 of stem, interrupted in proximal 2, paniculate, branched. Pedicels articulated in proximal 3, filiform, distinctly swollen in distal part (near base of tepals, but not at articulation point), 4-14 mm, articulation weakly evident, not swollen. Flowers 10-20 in whorls; inner tepals oblong-ovate, 4-6 × 3-5 mm, base rounded to subcordate, margins entire, apex obtuse or subacute; tubercles absent. Achenes mature specimens not seen. 2n = 120.

Flowering spring-summer. Seasonally wet habitats along streams; 2500 m; N.Mex.

Rumex tomentellus is known only from New Mexico and needs additional study. It may represent one of the southern North American elements of the R. aquaticus-R. occidentalis aggregate.