Ruth’s milkweed

Asclepias uncialis Greene subsp. ruthiae (Maguire) Kartesz & Gandhi; A. uncialis var. ruthiae (Maguire) Sundell

Herbs. Stems 1–8, decumbent, unbranched or branched near base, 9–10 cm, densely puber­ulent with curved trichomes, not glaucous, rhizomatous. Leaves proximally opposite, distally alternate, petiolate, with 0 or 1 stipular colleter on either side of petiole; petiole 2–5 mm, densely puberulent with curved trichomes; blade ovate to lanceolate, 2–3 × 0.8–2 cm, chartaceous, base truncate to cuneate, margins entire, apex acute, venation eucamptodromous, surfaces persistently pilosulous, more densely so on veins, margins densely ciliate, laminar colleters absent. Inflorescences terminal and extra-axillary at upper nodes, sessile, 2–6-flowered, bracts few. Pedicels 15–25 mm, densely pilosulous to tomentulose. Flowers erect; calyx lobes elliptic, 2–2.5 mm, apex acute, pilose to tomentulose; corolla red-violet, lobes reflexed with spreading tips, oval, 4–5 mm, apex acute, glabrous; gynostegial column 0.2–0.5 mm; fused anthers brown, cylindric, 1.5–2 mm, wings right-triangular, apical appendages ovate; corona segments red-violet dorsally, white proximally, sessile, cupulate, 1.5–2 mm, slightly exceeded by style apex, apex truncate with a proximal tooth on each side, glabrous, internal appendage falcate, included in cavity, glabrous; style apex shallowly depressed, pink to red-violet. Follicles erect to spreading on upcurved to spreading pedicels, ovoid, 3–3.5 × 0.7–1 cm, apex acuminate, smooth, pilosulous to tomentulose. Seeds broadly ovate, 8–9 × 6–7 mm, margin corky-winged, erose, faces rugulose, minutely hirtellous; coma 1–1.5 cm.

Flowering May–Jun; fruiting Jun–Jul. Slopes, terraces, bluffs, sandstone, basalt cobbles, limestone, sandy, clay, and rocky soils, desert scrub, shrubby grasslands; 1200–2000 m; Utah.

As discussed under Asclepias eastwoodiana, A. ruthiae is part of a complex of four species sometimes recognized as a single species. It is endemic to a small area in southeastern Utah (Emery, Sevier, and Wayne counties) on the periphery of the San Rafael Swell, the northeastern margin of Waterpocket Fold, and valleys north of the Henry Mountains. Reports from Arizona, New Mexico, and Monument Valley in Utah represent records of A. sanjuanensis. It commonly co-occurs with the similar A. macrosperma in this region and differs from the latter species by its more diminutive dimen­sions, red-violet corolla, and smaller, smooth fruit. Con­servation status of this species requires re-assessment in light of the recent recognition of its more limited range.