Cynanchum laeve (Michx.) Pers.

Climbing Milkweed

© SRTurner

Family - Asclepiadaceae

Stems - Twining, climbing, to 10 m, with clear sap, sparsely to moderately hairy, at least toward the tip, usually in longitudinal lines.

	Stem and node.
© DETenaglia

	Stem and node.
© SRTurner

	Sap.
© SRTurner

Leaves - Opposite, simple, petiolate. Petioles to 7 cm long, sometimes reddish. Blades 2-10 cm long, triangular-ovate to broadly ovate, the base deeply cordate, the basal lobes broadly rounded, the sinus of well-developed leaves often quadrate, glabrous or sparsely short-hairy, mostly along the veins.

	Leaves.
© SRTurner

	Leaf abaxial.
© SRTurner

	Leaf abaxial surface.
© SRTurner

Inflorescences - Axillary umbellate clusters of 5-40 flowers. Peduncles to 5 cm long, pubescent. Pedicels to 1 cm long, pubescent.

	Inflorescences.
© SRTurner

	Inflorescence (lateral view).
© SRTurner

	Inflorescence (top view).
© SRTurner

Flowers - Calyx lobes 1.5-3.0 mm long. Corolla deeply 5-lobed, the lobes 4-7 mm long, narrowly oblong to lanceolate, glabrous. Corona modified into 5 erect, lateral, petaloid segments, each segment 4-6 mm long, white, the basal portion oblong-ovate, the apical 1/3-1/2 divided into 2 erect, linear lobes.

	Calyces.
© SRTurner

	Corolla.
© DETenaglia

Fruits - Follicles 8-14 cm long, ovate to teardrop-shaped in outline, glabrous. Seeds with the body 7-9 mm long, obovate in outline.

	Fruit.
© SRTurner

	Immature fruit and seeds.
© SRTurner

Flowering - July - September.

Habitat - Bottomland forests, streambanks, pond margins, fields, gardens, fencerows, roadsides, railroads, open disturbed areas. Sometimes cultivated.

Origin - Native to the U.S.

Lookalikes - None.

Other info. - This species is present across much of Missouri, common in some areas, uncommon or absent in much of the Ozarks. Beyond Missouri its range is somewhat scattered, primarily within the U.S. Midwest. The plant is easily identified by its vining habit, opposite leaves which often have a deeply indented base with squared-off sides and small inflorescences of white flowers. Somewhat surprisingly, the flowers are very aromatic, with a pleasant floral scent. A vigorously flowering plant can perfume the air for a radius of several meters.

This plant is seen as a weed by some, possibly due to its predilection for fencerows, gardens, and other disturbed areas. It can be a problem weed in crop fields. However, it is a native plant which is beneficial as a larval food of monarch butterflies and milkweed tussock moths. The flowers attract bees and are excellent for honey production. The plant dies back in the fall, leaving the large fruits hanging until they split open dorsally. The seeds can be carried a great distance by the wind.

Unlike many other members of the family, this one has clear sap. However, there is some disagreement on this point among online resources, with various references describing the sap as "clear," "milky," or "cloudy." The last term describes a condition intermediate between the first two and may help explain the discrepancy. The sap in the image above appears faintly cloudy. It is possible that the appearance is variable and depends on the specimen or its environment.

Previously used synonyms include Ampelamus laevis, A. albidus, and Gonolobus laeve.

Photographs in St. Louis, MO., 7-28-03 (DETenaglia); also along the Katy Trail near Dutzow, Warren County, MO, 8-3-2012, Riverfront Park, Washington, Franklin County, MO, 7-17-2020, and Duck Creek Conservation Area, 8-17-2021 (SRTurner).