Oval-leaf or dwarf milkweed, asclépiade à feuilles ovées

Herbs. Stems 1, erect, unbranched, 30–70 cm, densely puberulent with curved tri­chomes or pilosulous to tomen­tose, not glaucous, rhizomatous. Leaves opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole; petiole 3–10 mm, densely pilosulous to tomentose; blade broadly ovate to oval or narrowly elliptic, 3–9 × 1.5–4.5 cm, chartaceous, base obtuse or rounded to truncate, margins entire, apex acute to obtuse, mucronate, venation brochidodromous, surfaces pilosulous abaxially, sparsely so adaxially except on veins, margins ciliate, 4–16 laminar colleters. Inflores­cences extra-axillary at upper nodes, sessile or pedunculate, 5–21-flowered; peduncle 0–7 cm, densely pilosulous to tomentose, with 1 caducous bract at the base of each pedicel. Pedicels 12–22 mm, densely pilosulous to tomentose. Flowers erect to spreading; calyx lobes lanceolate, 2–3 mm, apex acute, densely pilosulous; corolla cream to yellowish, lobes reflexed with spreading tips, elliptic, 5–7 mm, apex acute, pilosulous abaxially at apex, glabrous adaxially; gynostegial column 0.2–0.5 mm; fused anthers green, cylindric, 1.5–2 mm, wings right-triangular, closed, apical appendages ovate; corona segments cream to yellowish, subsessile, conduplicate, dorsally flattened, 3–4 mm, exceeding style apex, apex acute with proximal tooth on each side, glabrous, internal appendage falcate, exserted, sharply inflexed to ascending over style apex, glabrous; style apex shallowly depressed, cream to pinkish. Follicles erect on upcurved pedicels, lance-ovoid, 5–8 × 1.2–2 cm, apex acute to apiculate, smooth, densely pilosulous to tomentose. Seeds ovate, 5–6 × 3.5–4.5 mm, margin winged, faces rugulose; coma 2.5–3 cm.

Flowering May–Aug; fruiting Jul–Sep. Hills, slopes, ravines, bluffs, ridges, dunes, coulees, ditches, lake shores, sandstone, sandy, rocky, and clay soils, prairies, shrubby grasslands, aspen woods, oak savannas, oak woods, pine-oak and pine forests; 300–1600 m; Alta., Man., Ont., Sask.; Ill., Iowa, Mich., Minn., Mont., N.Dak., S.Dak., Wis., Wyo.

Asclepias ovalifolia is the northernmost-ranging species in the genus, and over much of its range co-occurs with at most one other species of Asclepias. The quality of its habitat has been degraded by woody encroach­ment, presumably resulting from fire suppression. It appears to be secure in the core of its range in Minnesota, North Dakota, Manitoba, and Saskatchewan. Elsewhere there are conservation concerns, as in Illinois (Cook, Kankakee, Kendall, Lake, and McHenry counties), Michigan (Lake and Menominee counties), Montana (Carter and Sheridan counties), Wyoming (Crook County), and Ontario. Asclepias ovalifolia was collected in 1915 in British Columbia in a valley of the Columbia Mountains (Bain. s.n. [UBC]), far disjunct from the species’ range east of the Rocky Mountains. The occurrence has been considered to be adventive and not persistent (F. Lomer, pers. comm.). It has been reported from Nebraska based on the original determination of what became the type specimen of A. hallii; it is not known to have ever occurred in that state. Hybrids with A. syriaca are known, but appear to be rare, and can be recognized by possession of intermediate floral and vegetative traits.