Eastwood’s milkweed

Herbs. Stems 1–6, ascending to decumbent, unbranched or branched near base, 6–30 cm, 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 2–10 mm, puberulent with curved trichomes; blade narrowly lanceolate to ovate, 2–4.5 × 0.6–3 cm, chartaceous, base cuneate to obtuse, margins entire, apex acute, mucronate, venation eucamptodromous, surfaces strigulose or pilosulous on midvein to glabrate, margins densely ciliate, laminar colleters absent. Inflo­rescences terminal and extra-axillary at upper nodes, sessile or pedunculate, 2–25-flowered; peduncle 0–4 cm, puberulent with curved trichomes to glabrate, bracts few. Pedicels 10–28 mm, pilosulous to puberulent with curved trichomes. Flowers erect; calyx lobes elliptic to lanceolate, 2–2.5 mm, apex acute, puberulent with curved trichomes to pilosulous; corolla red-violet, faintly striate, 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 conical, barely exserted from cavity, glabrous; style apex shallowly depressed, pink to red-violet. Follicles spreading to pendulous on spreading pedicels, lance-ovoid, 3.5–6 × 0.5–1 cm, apex acuminate, smooth, faintly striate, strigose. Seeds not seen.

Flowering May–Jun; fruiting Jun. Valleys, depres­sions, flats, slopes, arroyos, dunes, granite, gravel, sandy, calcareous, and clay soils, shrubby grasslands, desert scrub, pinyon-juniper woodlands; 1400–2200 m; Nev.

Asclepias eastwoodiana and the next three species (A. ruthiae, A. sanjuanensis, A. uncialis) form a complex of largely allopatric entities that have sometimes been united in a single species, for which the name A. uncialis holds priority (for example, E. Sundell 1994). However, each entity shows genetic, chemical, and subtle mor­phological distinctions, supporting recognition at the specific rank (M. B. Sady and J. N. Seibert 1991; J. P. Riser et al. 2019). Asclepias eastwoodiana is distinguished from the others by the differences in leaf shape, vestiture, and corona morphology indicated in the key. With A. ruthiae it shares a spreading to pendulous fruit that differs from the typically erect fruits of A. sanjuanensis and A. uncialis. Asclepias eastwoodiana is endemic to valleys in central Nevada (Esmeralda, Lander, Lincoln, Mineral, and Nye counties), where it is considered to be a species of conservation concern, potentially threatened by livestock trampling and mining development.