Green-flowered Milkweed - Asclepias asperula

Height: 1-2 feet tall, with spreading stems that form large, dense clumps.
Leaves: 4-8 inches long, narrow and irregularly grouped.
Flowers: Crowded into a ball-shaped head, 3-4 inches across, at the end of the flower stem, and are intricately arranged.

Perennial.
March-October

"Inside the partially divided petals is a crown, out of which extend 5 white stamens with large, balllike anthers, all symetrically arranged."

Sources:
Loughmiller. Texas wildflowers.
Photos: Courtesy of S. Peregrine Johnson, taken May, 2004.