Asclepias quadrifolia Jacq.
Family - Asclepiadaceae
Habit - Perennial forb from slender rhizomes.
Stems - Ascending to erect, to 50 cm, often purplish, often with one side flattened, sometimes branched near the tip, glabrous or pubescent in longitudinal lines, with 2-5 nodes, with milky sap.
Stem and leaf bases.
Leaves - Opposite, simple, short-petiolate, entire. Lowest leaves usually in whorls or false whorls (two opposite nodes in close proximity). Blades to 12 cm long, 7 cm wide, lanceolate to ovate, the base gradually narrowed or tapered, the tip tapered to a sharp point, the margins minutely ciliate, the surfaces with curly hairs mostly along the midvein.
Inflorescence - Umbels, terminal and upper axillary, usually 1-3 per stem, typically subtended by a pair of leaves, with 15-35 flowers. Pedicels to 2 cm long, pubescent, sometimes purplish pink.
Inflorescence and buds.
Flowers - Calyx lobes 5, reflexed, glabrous, 1-3 mm long, lanceolate to ovate. Corolla lobes 5, reflexed, glabrous, light pink to white, 4.5-6.0 mm long, lanceolate to elliptic-lanceolate. Gynostegium appearing stalked (the column visible below the bases of the hoods), white, the corona conspicuously longer than the tip of the anther/stigma head. Corona hoods whitish to pinkish tinged, glabrous, 4-5 mm long, spreading to loosely ascending, attached near their bases, oblong-elliptic in outline, the tips broadly rounded, the margins with a pair of triangular teeth or lobes at or below the middle, the bases not pouched. Horns white, glabrous, attached in the basal half of the hoods, arched over the anther/stigma head but not extended past the tips of the hoods, linear, not flattened, tapered to a sharp point at the tip. Column purplish, 2 mm long, white at apex. Pollinia 1 mm long, terminator deep purple. Pistils 2, green, 2 mm long, glabrous. Ovules numerous.
Fruits - Follicles 8-14 cm long, erect or ascending from mostly erect stalks, narrowly elliptic-lanceolate in outline, the surface smooth, glabrous or minutely hairy. Seeds with the body 7-8 mm long, the margins narrowly winged, the terminal tuft of hairs white or light cream-colored to tan.
Flowering - May - July.
Habitat - Rich or dry rocky open woods, on upland slopes or ridges.
Origin - Native to U.S.
Other info. - This pretty and delicate milkweed can be found throughout much of Missouri, with the exception of the northwestern and southeastern corners. Its U.S. distribution comprises a tight band in the Midwest, roughly centered on Missouri, and a second band extending along the Appalachians into the Northeast and Canada. The plant is easy to identify, with its diminutive stature and light pink to white flowers. The four leaf whorls referenced by the common name are not a reliable feature, since many individuals lack this arrangement. Even when present, the whorls are often closely spaced pairs of opposite leaf nodes rather than true whorls. The plant typically has only one or sometimes two false whorls of leaves on the stem.
Photographs taken at the Noblett Lake Recreational Area, Douglas County, MO., 5-18-01 (DETenaglia); also at Engelmann Woods Natural Area, Franklin County, MO, 5-9-2014 (SRTurner).