Welsh’s milkweed

Herbs. Stems 1–20, erect to ascending, unbranched, 35–100 cm, densely tomentose to gla­brate, not glaucous, rhizoma­tous. Leaves subopposite to opposite (alternate), sessile or petiolate, stipular colleters absent; petiole 0–8 mm, tomentose to glabrate; blade oblong or obovate to oval or ovate, 4.5–14.5 × 2–8 cm, subsucculent, base rounded to cordate, margins entire, apex rounded or truncate to emarginate or acute, mucronate, venation brochidodromous, secondary veins orthogonal, surfaces tomentose to glabrate, margins eciliate, 0–10 laminar colleters. Inflorescences extra-axillary from upper nodes, pedunculate, 22–80-flowered; peduncle 2.5–6 cm, densely tomentose, with 1 caducous bract at the base of each pedicel. Pedicels 10–15 mm, densely pilose to tomentose. Flowers erect to pendent; calyx lobes linear, 5–6 mm, apex acute, densely pilose to tomentose; corolla ochroleucous or tan to red-violet, lobes reflexed with spreading tips, oval to oblong, 5.5–6.5 mm, apex acute, densely tomentose abaxially, glabrous adaxially; gynostegial column 1–1.5 mm; fused anthers green to tan, obconic, 1.5 mm, wings triangular, widest at middle, closed, apical appendages ovate; corona segments cream to ochroleucous, sometimes green at base, shiny, stipitate, tubular, dorsally flattened, 2.5–3.5 mm, exceeding style apex, apex truncate, glabrous, internal appendage falcate with acicular tip, exserted, sharply inflexed over style apex, glabrous; style apex shallowly depressed, green. Follicles pendulous on spreading pedicels, ellipsoid, 5–7 × 1.7–3 cm, apex acuminate, softly muricate, densely to thinly tomentose. Seeds oval, 18–20 × 9–10 mm, margin winged, faces minutely rugulose; coma 4–4.5 cm.

Flowering May–Sep; fruiting Jun–Oct. Active orange to red sand dunes, adjacent to pinyon-juniper and pine woodlands; of conservation concern; 1400–1900 m; Ariz., Utah.

With respect to the number of populations, Asclepias welshii is the most endangered Asclepias in the flora area and is federally listed as threatened in the United States. Most of the populations are remote and relatively secure; however, the most accessible population in a Utah park has been subject to the impacts of off-road vehicle recreation. Leaves and stems of A. welshii emerge densely tomentose, but the lower portions of the plants become sand blasted and smooth as the season progresses. The species is strongly rhizomatous, as befits its shifting substrate. Seedlings and sprouts from rhizomes often bear narrowly linear leaves that differ so strongly from the foliage of more robust stems that they are not easily attributed to this species. Similar heterophylly is found in A. arenaria, A. erosa, and other milkweeds of sandy substrates.