Diphylleia grayi, the "skeleton flower" is normally opaque white but when it rains, the petals become transparent until the flower dries. Nanotechnologists are developing new materials inspired by the flower's structure that could lead to the likes of new underwater goggles that repel oil. From Mother Nature Network:
Skeleton flowers are native to wooded mountainsides in the colder regions of Japan, and they bloom from mid-spring to early-summer in shady conditions. The plant might be easier to spot if you look for its large, umbrella-shaped leaves. The pearly white (or clear, if it's raining) blossoms top the leaves in small clusters…
A related species, Diphylleia cymosa, can be found in the deciduous forests of the Appalachian Mountains here in the United States.
(via Daily Grail)