Oxalis oregana aka Redwood Sorrel

Oxalis oregana is known as redwood sorrel or Oregon oxalis. It belongs to the wood sorrel family, Oxalidaceae. Its native range runs from southwestern British Columbia to northwestern California. It grows in moist woods and redwood forests. Oregon populations also reach the Columbia River Gorge and western Cascades. This herbaceous perennial spreads through creeping rhizomes and forms low mats.

Height varies between sources. Oregon State gives about 0.2–0.3 feet [0.06–0.10 metres]. The RHS describes plants reaching about 0.7 feet [0.20 metres]. Its broader height range reaches 1.6 feet [0.50 metres]. Allow room for the mat to grow outward. The RHS records spread beyond 26 feet [8 metres]. It can keep spreading where woodland conditions suit it.

Each green leaf has three leaflets on a long stalk. Oregon State describes smooth upper surfaces, with hairs beneath and along the edges. The RHS lists the foliage as deciduous. Slender stems carry single flowers from spring through autumn. Flowers may be white, pale pink, rose-pink, or lilac. They reach about one inch across. Small, round fruits follow the flowers. These measure roughly a quarter to a third of an inch across.

Grow redwood sorrel in partial or full shade. Dappled woodland light also suits it. Give it fertile soil rich in humus. Keep the soil moist, but let excess water drain away. The RHS lists clay, loam, sand, and chalk as suitable. It also accepts acid, neutral, and alkaline soils. The RHS rates its hardiness H5. Plants For A Future gives USDA zones 6–9. Oregon State gives zone 7 as its lower limit.

Use it as ground cover in a shaded woodland garden. The RHS also lists containers, rock gardens, and informal gardens. Its spreading habit can become aggressive, so allow space around nearby plants. Weed around new plants during their first year. Divide established clumps in spring to make more plants. No pruning is needed. Pests seldom cause trouble, though rust may occur.

Plants For A Future lists the leaves and flowers as edible. Leaves can be eaten raw or cooked; flowers can be eaten raw. Both have a sour taste. Eat only small amounts because the leaves contain oxalic acid. Cooking lowers the amount, but heavy use can affect calcium supply. People prone to kidney stones or certain other conditions need extra caution. The same source records past use for sore eyes, skin complaints, and rheumatism. These are reports of traditional use, not proof of benefit.