16a. Boerhavia coulteri (Hooker f.) S. Watson var. coulteri
Boerhavia rosei Standley
Stems 2-8 dm. Leaf blades 10-50 × 6-32 mm. Flowers: pedicel 0.2-1.6 mm; bracts at base of per-ianth usually 2; perianth 1-2 mm distal to constriction; stamens 2-3(-4), slightly exserted. Inflorescences terminal clusters, axis 15-60 mm. Fruits (4-)7-20(-22) per cluster, usually overlapping by 50-100% of their length, or 2-4 in group, separated by small gap from next group and with distal fruits overlapping, pale tan, narrowly obpyramidal, 2.5-3.2(-3.6) × (0.9-1.1(-1.4) mm (l/w: [2.2-]2.5-3.1[-3.3]), apex bluntly conic-truncate, round-truncate, or truncate; ribs obtuse, each often with sharp ridge, slightly rugose near sulci; sulci 0.1-0.2 times as wide as base of ribs, slightly rugose.
Flowering late spring-early fall. Sandy or loamy soils in arid grasslands, among brush, roadsides in deserts and cultivated areas; [100-]500-1400 m; Ariz.; N.Mex., Utah; Mexico (Sinaloa, Sonora).
Most plants of Boerhavia coulteri var. coulteri have fruit apices that are bluntly conic- or round-truncate. Along the Santa Cruz River particularly, some plants have abruptly truncate fruits; those plants represent the phase known as B. rosei. Early in the twentieth century, J. J. Thornber proposed the name "B. standleyi" for such plants but never published it. P. C. Standley (1911) described the ribs of B. rosei as narrow, adding in 1918 that the sulci were broad and open. As the type demonstrates, the relative breadth of the ribs and sulci is exactly the reverse, confusing regional botanists for several generations.