Here’s a photo of Oxalis oregana, or redwood sorrel. I took this photo in May, within the California coast redwood forest of Prairie Creek Redwoods State Park. This was during an ecology field course.
Oxalis oregana, of the Oxalidaceae, is native to coastal British Columbia, Washington, Oregon, and California. This perennial groundcover grows in dense carpets under the shaded canopy of redwood and Douglas-fir forests. Redwood sorrel is a species that prefers shade–photosynthesizing at light levels of 1/200th of full sunlight. When it is too bright, the three heart-shaped leaves fold downward until it is shady again.
Not seen in this photograph are the delicate, pink to white flowers with five petals. This species also contains oxalic acid, leaving the edible leaves with a sour and tangy taste. This hints at the genus name Oxalis coming from the Greek oxys, meaning “sour”.