green milkweed

Green milkweed perennial herb rises from a taproot. The leaves and stems contain a milky juice. It is usually found as scattered, individual plants.

The stems are usually erect but sometimes recline on the ground with the tips ascending. They are thinly hairy and unbranched below the inflorescence.

There are 5 to 12 pairs of leaves per stem. The leaves are opposite, 1½″ to 5½″ long, ¼″ to 2½″ wide, pointed at the tip, and highly variable in shape. They are usually lance-shaped. In favorable conditions they may be broadly inversely egg-shaped, broadly oval, or nearly circular. In dry areas they are often long, linear lance-shaped, and very narrow. They are attached to the stem on short leaf stalks. The margins are untoothed and wavy. The lower surface is downy.

Leaf shape of this species is highly variable. Some authorities recognize up to three varieties based on the shape of the leaves: var. lanceolata, var. linearis, and var. obovata. However, there is a near continuum of leaf shape from nearly circular to nearly linear, making delineation by leaf shape impossible.

The inflorescence is usually 1 to 3 dense, umbrella-like clusters (umbels) near the top of the stem. They are attached to the side of the stem near the upper leaf nodes. They do not arise from the leaf axils. The clusters are 2″ to 3″ in diameter, are on a short stalk, and droop downward. They typically have 20 to 80 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 ⅓″ to ½″ tall. The petals are light green. 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 hoods are light green or greenish-white. They have no horns.

The fruit is a narrow, spindle-shaped pod. It is 3″ to 6″ long and ½″ to 1″ wide. It is held erect or ascending on an erect stalk.

8″ to 20″

Light green

Oval-leaf (Asclepias ovalifolia) leaves are smaller, 2″ to 3″ long. The leaf margins are not wavy. The inflorescence is a loose cluster of 5 to 20 flowers. There is one cluster at the end of the stem and possibly 1 or 2 clusters in the uppermost leaf axils. The flowers are greenish-white or greenish-purple, and have horns within the hoods.

Prairie milkweed (Asclepias hirtella) is a much taller plant, 16″ to 40″ tall at maturity. The leaves are longer and narrower, lance-shaped to linear, and alternate. It has 2 to 10 flower clusters. The flowers are tinged with purple. The petals are separated from the hoods by a distinct column.

Whorled milkweed (Asclepias verticillata) has extremely narrow, linear leaves in whorls of 3 to 6. The flower heads have only 10 to 20 flowers. The flowers have horns within the hoods. The petals are separated from the hoods by a distinct column.

Dry. Prairies, fields, upland woods, inland sands, barrens, roadsides.

June to August

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, 24, 28, 29, 30.

Native

Flowering plant

Flowering plant

Inflorescence

Broad leaves

Broad leaves

Infructescence

Fruit

Asclepias viridiflora
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