The Redwood Sorrel (Oxalis oregana) occurs from Vancouver Island south to northern California. It makes a beautiful groundcover in moist, shady areas. We photographed it at Van Dusen Botanical Garden in Vancouver where it forms a carpet under Rhododendrons. The leaves have a sour taste, which indicates the presence of oxalic acid. Although edible it should only be consumed in small quantities since it could cause kidneystones.