Oxalidaceae   -   Sorrels

Oxalis  Linnaeus 1753

Oxalis is a large genus with over 800 species widely spread in the tropics and temperate regions with the exception of Australasia. Many species come from South Africa and South America. Leaves are alternate and typically divided into 3 - 5 leaflets that undergo marked daily movements, although a few species have simple leaves. The bisexual regular flowers have 5-fold symmetry, with 5 sepals, 5 petals, ten stamens in two rings of five and five styles each with a superior basal ovary. Flowers often close at night or in dull weather and some species e.g. Oxalis acetosella (Wood Sorrel) may produce viable seeds without opening (cleistogamous).
 
The ovary develops into a 5-chambered fruit which is usually a capsule but may be a berry. Some species have explosively dehiscent fruits as a very effective mechanism for seed dispersal. Seeds may have a fleshy aril that spontaneously inverts itself to catapult the seed from the pod. Because of this, some members of the Oxalidaceae are invasive weeds and may disperse themselves through the greenhouse with volunteer seedlings coming up in every pot. A non-succulent species Oxalis corniculata (creeping wood sorrel), with small yellow flowers, will be familiar to many cactus collectors and is difficult to eradicate.
 
A few South American species of Oxalis are stem succulents and some South African species produce small to medium-sized tubers. Some of these tubers are edible and cultivated for food, and leaves can also be eaten. However, excessive consumption of leaves containing oxalate may lead to loss of bone density. Several species have somewhat fleshy leaves.