Oxalis tetraphylla aka Iron Cross Oxalis

Oxalis tetraphylla is a small perennial in the wood sorrel family, Oxalidaceae. Its native range runs from Mexico into Central America. It grows in a subtropical climate and rests below ground between growing seasons. Gardeners know it as lucky clover or four-leaved pink sorrel. The RHS lists Oxalis deppei as a synonym. It is not native to Britain or Ireland. Plants have escaped gardens and become established in tropical areas.

The plant forms clumps and can spread into a low mat. Sources describe plants around 0.3–0.5 feet (0.10–0.15 metres) tall. The RHS gives a broader garden height range of 0.3–1.6 feet (0.10–0.50 metres). Its listed spread covers the same range. Green leaves look like clover leaves, with heart-shaped leaflets. A brown stripe marks each leaflet near its base. The plant sheds its leaves and rests for about five months. Dense summer growth can cover the soil during its active season.

Pink flowers shaped like funnels bloom from spring into early autumn. Insects pollinate the flowers. The RHS suggests this plant for rock gardens, slopes, and beds. It also suits pots, hanging baskets, and growing under glass. Its low growth makes it useful as summer ground cover. PFAF reports that it covers ground in sun or light shade. The long rest period means this cover does not last all year.

Give it a sheltered site with full sun and good drainage. The RHS recommends soil with few nutrients, including sand or loam. It accepts acidic, neutral, or alkaline soil. Soil may be moist, but water must drain away. Under glass, the RHS suggests equal amounts of loam, leaf mould, and grit. It rates the plant H4; PFAF lists USDA zones 7–10. Plants can take two to five years to reach full size. Raise new plants from seed or divide existing clumps. They need no pruning. Slugs, snails, and rust may cause problems. Sources disagree on weed risk; records include weeds in cultivated Jersey soil.

Leaves and flowers have a tart taste and are edible. Eat leaves raw or cooked, but only in small amounts. Cooking lowers their oxalic acid content. Too much can reduce the calcium available to the body. People prone to kidney stones, gout, or arthritis should take care. The cooked root contains starch but has little food value. PFAF records no known medicinal use.