Rumex orthoneurus K. H. Rechinger

Rumex orthoneurus has been reported from northern Mexico (M. Fishbein 1993). The species is in the Center for Plant Conservation's National Collection of Endangered Plants.

Plants perennial, glabrous or indistinctly papillose-pubescent especially on leaf blade veins abaxially, with creeping or fusiform rhizomes. Stems erect, branched above middle (only in inflorescence), 60-100 cm. Leaves: ocrea deciduous or partially persistent at maturity; blade with lateral veins ± equal in size, oblong or oblong-lanceolate, 20-40(-50) × 8-15(-18) cm, more than 3 times as long as wide, base broadly cuneate, obtuse, or weakly cordate, margins entire, flat, apex acute, subacute, or acuminate. Inflorescences terminal, occupying distal 1/ 2 of stem, often dense, narrowly paniculate. Pedicels articulated in proximal 1/ 2, filiform, (5-)12-15(-17) mm, articulation indistinct, scarcely visible. Flowers 10-20 in whorls; inner tepals ovate-deltoid, 4.5-7 × 3.5-7 mm, widest in proximal 3, base truncate or weakly emarginate, margins erose to weakly serrate or indistinctly denticulate in basal part, apex acute to acuminate; tubercles absent. Achenes brown, 2.5-4 × 1.5-2.5 mm. 2n = 120.

Ariz.; N.Mex., Mexico (Sonora).

Flowering late spring-summer.

Along streams; 2500m.

Rumex densiflorus Osterhout subsp. orthoneurus (Rechinger f.) Á. Löve