Yellow Sorrel (Oxalis stricta) Also called yellow wood sorrel, it is a native North American plant (also found in Eurasia) and grows from underground stems (rhizomes). The leaves are most often green, but may also be purplish or brownish red. Its leaves fold up at night and open again in the morning. It also folds its leaves when under stress, such as when growing in direct sun or during storms. The plant may reach 6-15" in height. It prefers moist soil and partial shade, but is also commonly found growing in cracks in sidewalks. The yellow spring/summer flowers are about a half-inch in diameter. They may occur singly or in clusters of up to five flowers. Wood sorrels are also called sourgrasses or shamrocks. They are delicate, and yet can withstand being walked on, mowed to within a quarter inch and poisoned. It'll grow in sun or shade, good soil or poor. And, it is an edible plant. The whole plant produces an orange to yellow dye.