Seeds from this Spider Milkweed. A native to southwestern United States and northern Mexico it is hardy in zones 9-11. It is also known as green-flowered milkweed, and Spider Milkweed. It is a perennial plant growing to 1-2 feet tall, with clustered greenish-yellow flowers with maroon highlights. It blooms from April through June, and favors moist, sandy or rocky soil. A. viridis is a food for Monarch caterpillars. This Asclepias can be poisonous to animals and humans if consumed.