Antelope Horns or Green-flowered Milkweed or Spider Antelope Horns Apocynaceae:
Asclepias asperula is a late spring blooming species that grows one to two feet tall. The flowers are in clusters and greenish-yellow colored with maroon highlights. It blooms from April through June, and favors moist, sandy or rocky soil. It is food for Monarch caterpillars and contains alkaloids that the Monarchs absorb and retain which makes them unpalatable and poisonous to predators.
Zones 7-9. Soak seeds in hot water for 36 hours, changing the water with fresh water every 12 hours, Start with 4 weeks at 39ºF moist, move to 68ºF for germination. Surface sow, light needed for best germination in 1-3 weeks at F 75. If little germination in 3 weeks, chill pots for 40 days. This species is native from southwestern United States and northern Mexico.