Antelope horns (Asclepias asperula), Alibates Flint Quarries National Monument, 2015.

A member of the milkweed family, Asclepias, Antelope horns are also known by the moniker spider milkweed. Named for its elongated seed pods, the plant forms clumps that may grow to 2' in height. Flowers appear in these crowded, round clusters up to 4" wide. Look for the five symetrically-arranged stamens (as in the photo) with large, ball-like anthers. Interestingly, you have probably already heard that milkweed plant species such as this are the sole source of food for the milkweed butterfly or, as you may know it referred to, the monarch butterfly.