The common names of Oxalis genus members sometimes seem to be the result of a mix-and-match game using the terms wood-sorrel, oxalis, creeping, western (or eastern), and sorrel, among others. Add to that the color descriptors and the honorifics used as the species and it is sometimes difficult to know which plant is under discussion.
Last spring I mentioned a white Oxalis, Oregon sorrel. A yellow member of the Oxalis genus is western yellow oxalis (O. suksdorfii), or western wood-sorrel, Suksdorfs sorrel, western yellow sorrel, creeping oxalis – you get the idea!
There are several yellow sorrels that look very similar and are difficult to distinguish. They are all perennials with creeping rhizomous stems and clover-like compound leaves with three-heart shaped leaflets. The leaves open under shady conditions and fold in bright sunlight. All have five-petaled yellow flowers with more or less reddish veins atop long stalks. The plants contain a sour, watery juice. Western yellow oxalis is identified by its longer petals which are 1/2 to 3/4 inches long. One or two flowers sit atop a long peduncles (stems supporting the flowers) while the entire plant is covered in fine hairs.
A native of the western United States, western yellow oxalis can be found in the mixed evergreen forests of the Pacific Coast states.
Like Oregon sorrel the leaves can be eaten and I occasionally do nibble one or two on the trail. Their tart taste is refreshing. As the genus name suggest though, wood-sorrels contain oxalic acid, which can be harmful in large amounts. Thus I do not collect the delicate leaves for culinary uses.
In the shade wood-sorrel leaves open fully and are held horizontally, most likely to capture the maximum sunlight in the dark environment. At night and in full sunlight the leaves crease downward and “close”, perhaps to conserve moisture. I enjoy sitting and watching a patch of oxalis leaves open and close as twilight falls or the shadows change. It takes about 6 minutes for the leaves to close and about five times as long for them to open.
The species name of western yellow oxalis honors German-born Wilhelm Nikolaus Suksdorf (1850-1932), a pioneer botanist in the Pacific Northwest.
These western yellow oxalis plants were growing along the North Umpqua Trail in Oregon downstream from Wright Bridge.