Four-leaf or whorled milkweed, asclépiade à quatre feuilles

Herbs. Stems 1, erect, unbranched, 25–60 cm, puber­ulent on 1 side with curved trichomes to glabrate, not glau­cous, rhizomes absent. Leaves opposite, 2 mid-stem pairs usually with shortened internode forming a pseudo-whorl, petio­late, with 1 stipular colleter on each side of petiole; petiole 2–7 mm, puberulent with curved trichomes; blade ovate to elliptic, 2.5–12 × 1–6 cm, membranous, base cuneate, margins entire, apex acute to attenuate or acuminate, venation eucampto­dromous, surfaces inconspicuously puberulent on veins with curved trichomes, margins ciliate, laminar colleters absent. Inflorescences terminal, sometimes branched, and usually also extra-axillary at upper nodes, sessile or pedunculate, 7–31-flowered; peduncle 0–3.5 cm, puberulent on 1 side with curved trichomes, with 1 caducous bract at the base of each pedicel. Pedicels 17–28 mm, puberulent on 1 side with curved trichomes. Flowers spreading to pendent; calyx lobes lanceolate, 1.5–2 mm, apex acute, glabrous; corolla pink or cream, lobes reflexed, elliptic, 4–5 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially; gynostegial column 0.5–1.5 mm; fused anthers tan to brown, cylindric, 1–1.5 mm, wings right-triangular, closed, apical appendages ovate; corona segments pink or cream, sometimes striped pink dorsally, sessile, conduplicate, flattened dorsally, 2.5–4 mm, exceeding style apex, apex obtuse, oblique, glabrous, internal appendage subulate, exserted, arched to sharply inflexed over style apex, glabrous; style apex shallowly depressed, cream to pale pink. Follicles erect on straight pedicels, narrowly fusiform, 8–16 × 0.4–1 cm, apex long-attenuate, smooth, sparsely puberulent with curved trichomes to glabrate. Seeds ovate, 6–7 × 4–5 mm, margin winged, faces rugulose; coma 3–4.5 cm.

Flowering (Mar–)Apr–Aug(–Sep); fruiting May–Nov. Ridges, slopes, valleys, flats, lake shores, canyons, limestone, chert, sandstone, oak woods, oak-hickory, pine-oak, and mixed-hardwood forests, prairie open­ings; 100–800 m; Ont.; Ala., Ark., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., Md., Mass., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Vt., Va., W.Va.

Asclepias quadrifolia is small statured compared to the other deciduous forest milkweeds. It is found predominantly on slopes of eroded, sedimentary rocks, especially cherty limestone. Like A. purpurascens, it is distributed primarily in the Appalachian and Ozark mountains. Populations with pinkish flowers are lovely in early spring; other populations have a more washed-out coloration. The characteristic pseudo-whorl of four mid-stem leaves is not always present. Like other for­est milkweeds, it has experienced large population reduc­tions at the northeastern margin of its range due to habitat loss. It is considered to be extirpated from Delaware and to be rare and of conservation concern in New Hampshire, Rhode Island (Providence County), and Ontario (Prince Edward County), as well as to the west in Kansas (Cherokee County). It has been reported, but not verified, from Minnesota. Putative hybrids with A. exaltata have been documented very rarely from the Appalachian Mountains and can be recognized by intermediate floral and vegetative traits.