Antelope Horns ("Asclepias asperula") is a species of milkweed plant. It is also known as Green-flowered Milkweed, Spider Antelope Horns and Spider Antelopehorns. It belongs to the subfamily Asclepiadoideae. It is native to the southwestern United States and northern Mexico. It blooms from April to June. This species likes to grow in moist sandy or rocky soil. Antelope Horns grows from 0.3 to 0.6 meters (1-2 feet).