Tufted milkweed

Herbs. Stems 1–5, erect, unbranched, 6–15 cm, taller on vegetative or post-reproductive plants, densely tomentose to glabrate, not glaucous, rhizomes absent. Leaves opposite, petio­late, with 1 stipular colleter on either side of petiole; petiole 3–4 mm, tomentose to glabrate; blade orbiculate to obovate or oblate, 1.5–3.2 × 1.7–4 cm, much larger on vegetative or post-reproductive stems, subsucculent, base rounded to cordate, margins entire, apex truncate or emarginate to rounded or obtuse, venation eucamptodromous, surfaces tomentose to glabrate, laminar colleters 0–10. Inflorescences terminal, sometimes also extra-axillary, pedunculate, 5–28-flowered; peduncle 2.7–6 cm, tomentose, with 1 bract at the base of each pedicel. Pedicels 12–20 mm, densely pilosulous to tomentulose. Flowers erect; calyx lobes ovate to lanceolate, 1.5–2.5 mm, apex acute, pilose to tomentulose; corolla pinkish violet to tan, striate, lobes reflexed, oval, 4–5 mm, apex acute, glabrous abaxially, minutely papillate at base adaxially; gynostegial column 0.2–0.5 mm; fused anthers brown, cylindric, 1–1.5 mm, wings curved, closed, apical appendages ovate, erose; corona segments white apically, red-violet basally, sessile, conduplicate, dorsally rounded, 2.5–3 mm, equaling or exceeding style apex, apex truncate, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, glabrous; style apex shallowly depressed, cream to pink. Follicles erect on upcurved pedicels, lance-ovoid, 4–7.5 × 1.2–1.5 cm, apex long-acuminate, smooth, tomentose. Seeds broadly ovate, 6–7 × 4–5 mm, margin winged, corky, erose at chalazal end, faces papillose-rugulose, hirtellous; coma 1.5–2.5 cm.

Flowering Mar–May; fruiting May–Aug. Hills, slopes, ridges, flats, arroyos, canyons, rhyolite, granite, sandstone, limestone, igneous outcrops, rocky, gravel, sandy, chalky, or clay soils, oak, oak-juniper, pinyon-juniper, and riparian woodlands, pine-oak forests, desert and oak grasslands; 1100–1900 m; Ariz., N.Mex., Tex.; n, c Mexico.

Asclepias nummularia is the only milkweed in the flora area with small stature and obovate to orbiculate leaves that are bluish under dense tomentum until late in the season. The plants often bear an uncanny resemblance to tiny cabbages. Fruit set may fail across broad regions in some years, perhaps due to drought, although the adequacy of pollination in this species has not been studied. Unlike many species of Asclepias, post-reproductive and non-reproductive plants of A. nummularia often persist until frost. Coupled with the early flowering of this species, vegetative plants are observed and collected far more often than reproductive ones. Some plants persisting into the fall months have much larger leaves and longer stems, especially in shady or moist habitats; these have often been mistaken for A. latifolia, the range of which only barely overlaps that of A. nummularia in Grant County, New Mexico. Asclepias nummularia is not common in New Mexico, where it has been found in Grant, Hidalgo, and Sierra counties, and is only locally common in Texas in the Davis Mountains (Jeff Davis County), and additionally in Brewster and Presidio counties. Populations from San Luis Potosí and south with narrower leaves have been segregated as A. nummularioides W. D. Stevens; recognition of this taxon requires further evaluation.