Flower:

Flowers are in a densely packed round cluster about 2 inches across arising from a leaf axil. Individual flowers are pale green, ¼ inch across and ½ inch long with a 5-parted crown and 5 petals that pull straight back away from the crown, sometimes flaring a bit. Sometimes there is a purplish tint to the flowers. Each plant has 1 to a few clusters.

Leaves and stem:

Leaves are toothless, may have short hairs especially along the veins, are mostly opposite, though some may be alternate, and are very short stalked. Leaf shape is quite variable, from linear to lance-oblong. Linear leaves are often somewhat folded lengthwise, up to 6 inches long, less than 1 inch wide, smooth or somewhat wavy around the edges, straight or arching, usually pointed at the tip.

Lance-oblong leaves are typically shorter, up to 2½ inches wide, often very wavy along the edges and usually pointed at the tip. Stems are covered in short matted hair and may be tinged purple. Plants may be erect but tend to lean over.

Fruit:

Fruit is a smooth, spindle-shaped pod about 3 inches long that contains numerous flat brown seeds with a tuft of white hair to carry it off in the wind.

Notes:

Green Milkweed with linear leaves somewhat resembles the rare Narrow-leaf Milkweed (Asclepias stenophylla), which has even narrower leaves (¼ inch wide) and whiter flowers with more flaring petals, and also the rare Prairie Milkweed (Asclepias hirtella), which has stiffer, ascending leaves, and flowers have more flaring petals plus a distinct gap between the petals and crown. Plants with lance-oblong leaves somewhat resemble the rare Clasping Milkweed (Asclepias amplexicaulis), which has stalkless, clasping leaves and typically a single flower cluster at the top of the stem.