clasping milkweed

not listed

N5 - Secure

S3 - Vulnerable

Threatened

Clasping milkweed is an erect perennial forb. It occurs in the United States from New Hampshire to Minnesota south to Florida and eastern Texas. It is rare in Minnesota, where it is found in the driftless area in the southeast, and on just a single site in Dakota County.

Clasping milkweed rises on a single stem from a deep rhizome. The leaves and stems contain a white milky latex.

The stems are erect or sometimes recline on the ground with the tip ascending. They are stout, unbranched, hairless, and covered with a whitish, waxy coating (glaucous).

There are 2 to 5 pairs of opposite leaves. The leaves are thick, 2¾″ to 6″ long, ¾″ to 3″ wide, and oval or broadly oblong. They are attached to the stem without leaf stalks. They are rounded or heart-shaped at the base and rounded or broad-angled but not pointed at the tip. The base of the leaf partly surrounds (clasps) the stem, and frequently overlaps the base of the adjacent leaf. The upper surface is dark green and glaucous, the lower surface light green and glaucous. The margins are untoothed and strongly wavy.

The inflorescence is a single large, loose, umbrella-shaped cluster (umbel) rising on a very long stalk at the end of the stem. The stalk is 4″ to 12″ long with short, fine, soft hairs on just ½ or ⅔ of their circumference, the rest being hairless. The clusters are 3″ to 4″ in diameter and erect. They typically have 18 to 60 flowers.

The structure of the typical milkweed flower is unique and instantly recognizable. There are 5 petals bent backward at the base and hanging downward. Subtending the petals are 5 much shorter, light green, lance-shaped sepals. There are 5 stamens. Formed from the filament of each stamen is a petal-like appendage. The appendage consists of a tubular hood surrounding an awl-shaped horn in the center of the hood. The stamens and the stigma are fused together into a crown-like structure (gynostegium). Each stigma has a long slit designed to catch the legs of a pollinating insect. A small, dark, sticky gland above this slit is attached to pollen sacs from adjacent anthers. These glands are designed to break off as an insect pulls its leg free of the slit, and remain attached to the insects leg. The flowers are pollinated by larger insects strong enough to lift off with the pollen sacs attached. Smaller insects are caught in a death trap or leave behind their detached legs.

The flowers of this plant are shaped like the typical milkweed flower. They are ⅝″ to ¾″ tall on 1″ to 1¾″ long flower stems. The petals are green tinged with red or purple. They bend backward at the base, hang downward, then curl upward near the tip. They are separated from the hoods by a short but distinct column. The hoods are pink. The horns are much longer than the hoods. They project from the hoods and curve inwards.

The fruit is a long, thin, pointed, spindle-shaped pod. It is 3½″ to 6″ long and ⅓″ to ⅔″ thick. It is mostly hairless and glaucous. It is held erect or horizontally on a drooping stalk. It opens on one side exposing the seeds to spreading by the wind. The seeds have a tuft of white, silky hairs at the tip.

1′ to 3′

Petals green tinged with red or purple, hoods pink.

Common milkweed (Asclepias syriaca) stems are covered with short, matted or tangled, soft, woolly hairs. The leaves taper to a point at the tip and do not clasp the stem at the base. They are softly hair on the upper surface, and are not glaucous on the under surface. The leaf margins are not wavy. There are several umbels appearing in the upper leaf axils. The umbels are drooping and have up to 130 flowers. The flowers are pale purple or pink. The horns are shorter than the hoods. The pods are fat and are covered with warts.

Dry. Prairies, wood openings, open woods, roadsides, railroads. Full or partial sun.

June to July

Milkweeds are the only plants that Monarchs lay their eggs on. The eggs are laid on the underside of healthy young leaves.

This and other milkweeds contain cardiac glycosides and may be poisonous to both humans and livestock.

Sources

2, 3, 4, 5, 6, 7, 28, 29, 30.

Native

Rare in Minnesota

Clasping milkweed Asclepias amplexicaulis at TNC Cox Unit

Landscape at TNC Cox Unit with Clasping milkweed Asclepias amplexicaulis at lower center

At TNC Cox Unit with Clasping milkweed Asclepias amplexicaulis at lower center

Landscape TNC Cox Unit Clasping milkweed Asclepias amplexicaulis

Clasping milkweed Asclepias amplexicaulis at TNC KWD Cox Unit

Location: Weaver Dunes Preserve, Cox Unit

Location: Weaver Dunes Preserve, Cox Unit

Location: Wabasha County