oval-leaf milkweed

not listed

NNR - Unranked

SNR - Unranked

not listed

Oval-leaf milkweed is listed as endangered in Illinois and Michigan, threatened in Wisconsin. It is not listed in Minnesota.

Oval-leaf milkweed is a 8″ to 24″ tall, erect, perennial forb. A single stem, occasionally two, rises from a slender rhizome. The leaves and stems are velvety and contain a milky juice.

The stems are erect, usually unbranched, and covered with silky hairs. It usually has 4 to 6 pairs of leaves.

The leaves are opposite, untoothed, 2″ to 3″ long, and lance-shaped to oblong. They are rounded at the base. They are attached to the stem on leaf stalks up to ⅓″ long and are held erect or spreading. The lower surface is covered with fine hairs.

The inflorescence is usually a single, loose, umbrella-shaped cluster (umbel) at the end of the stem. Sometimes, there are 1 or 2 additional clusters rising from the uppermost leaf axils. The clusters are 2″ to 3″ in diameter, and typically have 5 to 20 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 ⅛″ to ½″ tall, less than ¼″ wide, and are attached by hairy stalks that are about 1″ long. The petals are greenish-white or greenish-purple. They bend backward at the base, hang downward, then curl upward near the tip. They are attached directly below the hoods without a separating column. The horns are shorter than the hoods. They project from the hoods and are curved inwards.

The fruit is a narrow, spindle-shaped pod. It is 2⅛″ to 3⅛″ long and about ⅜″ wide. It is held erect or ascending on an erect stalk. It opens on one side exposing the seeds to spreading by the wind. The seeds have a tuft of hairs at the tip that are light brown and ¾″ to 1⅛″ long.

8″ to 24″

Greenish-white or greenish-purple

Green milkweed (Asclepias viridiflora) leaves are larger, 1½″ to 5½″ long and up to 2½″ wide. The leaf margins are wavy. The inflorescence is a dense cluster of 20 to 80 flowers. The clusters are attached to the side of the stem near leaf nodes, not in the leaf axils and not at the end of the stem. The flowers are light green. The hoods have no horns. The fruit is much longer, 3″ to 6″ long.

Prairie milkweed (Asclepias hirtella) is a much taller plant, 16″ to 40″ tall at maturity. The leaves are much longer and narrower. They are 4″ to 8″ long, ⅛″ to ½″ wide, lance-shaped to linear, and alternate. It has 2 to 10 dense flower clusters with 30 to 100 flowers in each cluster. The flowers are tinged with purple. The petals are separated from the hoods by a distinct column. The hoods have no horns. The fruits are longer, about 4¾″ long. The tufts of hair attached to the seed tips are whitish.

Whorled milkweed (Asclepias verticillata) is a much shorter plant, 8″ to 20″ tall at maturity. The leaves are extremely narrow, linear, and in whorls of 3 to 6. The flower heads have only 10 to 20 flowers. The flowers have horns within their hoods.

Dry. Prairies. Sandy soil. 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, 7, 28.

Native

Uncommon

Plant

Flowering Plant

Fruiting Plant

Inflorescence

Leaves

Stem

Fruit