Asclepias asperula

Asclepias asperula is a species of milkweed plant. It is commonly known as antelope horns, 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).

Other websites

Asclepias asperula at USDA PLANTS Database
Asclepias asperula at Kansas Wildflowers and Grasses 

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