Asclepias viridiflora

I've only seen this plant in Indiana, though it also occurs in the southwest. It's uncommon in Indiana, the only population I saw was in limestone barrens.

A flowering stem at Baseline Barrens, south of Salem, IN, 6/27/04.

Side view of flowers at Baseline Barrens, 6/27/04.

Front view of flowers at Baseline Barrens, 6/27/04.