Asclepias subverticillata is a small-flowered milkweed. Leaves are narrow, often in 3-leaved whorls. Flowers are white to cream-colored. Plant height is mostly 12 to 24 inches, though plants can be taller. Horsetail Milkweed primarily occurs south of Interstate 70, but is has been found further north, as well. Plants grow on dry, gravelly sites or along ditches and streams.