whorled milkweed

Asclepias verticillata, in the Milkweed Family, as one would expect, and all their flowers have a somewhat unique relationship with butterflies; the monarch being one.

In this unique design, the actual "petals" in the corolla are reflexed. They are the pointed greenish leaf-like shapes behind the white "flowers". The white parts are "hoods" made from the stamens and horns made from anther filaments, in a "corona", a petaloid appendage of the stamens inside the corolla behind it, and the actual anthers are fused to the stygmas. The pollen is in sacs at the base of these hoods, and these sacs attach to the feet of visiting butterflies, ants, bees, and wasps, and after opening after drying out, it opens up to expose the pollen and gets deposited in other flowers's stigmas by the insects.

The flowers are in umbels of maybe 2-3 inches in diameter and each flower is about 8 mm in diameter roughly. For reference the long, nodular leaves you see in the image are about 1/8" wide (3mm).

Anyway K-5, Tamron 90mm, f/22, 1/180s, ISO 800 hand-held.