Milkweed is native to the Americas and are best known as being the source of food for Monarch butterfly catapillars.
There flowers are about a quarter inch across and grow in clusters. Here is what Wikipedia says about them:
[Milkweed] produce some of the most complex flowers in the plant kingdom, comparable to orchids in complexity. Five petals reflex backwards revealing a gynostegium (fused stamen filamens and styles) surrounded by a five-membrane corona. The corona is composed of a five paired hood and horn structure with the hood acting as a sheath for the inner horn. Glands holding pollinia are found between the hoods.
Here is a cluster of flower buds, the flowers lower down on the plant open first and the ones near the top of the plant open later.
This cluster has some flowers that have opened and some that have not.
I took all these photos with a Nikon D800 camera.