'T is moonlight in my garden; like some fair babe at rest,
The day-flower folds its silky wing upon its
Nor is it vain philosophy to think that plants may keep
A holiday of airy dreams beneath their graceful sleep.
From "My Garden" by Caroline Gilman
This member of the Spiderwort family, a native of Asia, has a distinctive flower consisting of two deep-blue petals arranged in a V-shape, with an inconspicuous, nearly hidden white petal at the point of the V. Until you're up close, the small flowers do not stand out amongst the foliage, and each flower lasts just one day.
This plant is found in moist conditions, often along streams.