There are some 500 species of Oxalis, and, since some of them are very invasive weeds, the genus has gotten a bad reputation. However, there are some species which aren't invasive at all, and which bear very pretty flowers and attractive, clover-like leaves.

Oxalis bowiei -- Bowie's Woodsorrel -- Very large bright green leaves with heart-shaped leaflets and umbels of large, cup-shaped, deep rose-pink flowers. A prolific and long blooming period in summer, flowers opening in sun. This is a South African native now naturalized in Australia. Rated at zone 9. We've found many South African bulbs hardy to zone 8 with excellent drainage and a winter mulch, but have not tried this one.

Oxalis megalorhizza, Galopagos Sorrel is, frankly, one of the invasive kind, but it's not offered here as a garden plant. Anyway, it's not hardy in most of the US. It's a tropical Oxalis from the Galapagos Island, with pale yellow flowers that stand above the rounded, rather succulent, glossy green leaves. The stem becomes enlarged and rough, covered by brown leaf scales, so the plant can come to resemble a miniature tree, often gnarled and twisted, with ersatz bonsai potential, or just as an oddity from the place where oddities showed Darwin how species originated.