Oxalis

Oxalis, commonly called sorrel, is a genus of mainly perennial, geophytic herbs, forming part of the Oxalidaceae family. There is only one more genus of this family occurring in southern Africa, viz. Biophytum.

The plants grow from corms, tubers or tuberous roots, the only dicotyledonous genus that in some species grows from corms. Bulb, corm or tuber shape is often an important part of species identification.

Some plants, like the one in picture, grow stems, while others are stemless, the radical leaves then growing in a basal tuft.

The plants contain sour, acidic sap, called oxalic acid, found in some other, related, flowering plants as well. The generic name, Oxalis, is derived from the Greek word, oxys, meaning sharp, pungent or acid and -alis meaning resembling or pertaining to, referring to this sap.

The leaves are basal or alternate, digitately three-foliolate to many-foliolate or pinnately three-foliolate, rarely one-foliolate. Leaflets have entire margins, roundly shaped, notched to bilobed or obcordate, the stalk emerging from the tip of the heart-shape, not between the lobes. Some species have stipules.

Flower stalks mainly emerge from the leaf axils. The regular, radially symmetric (actinomorphic) flowers grow solitary or in umbel-like clusters. There are five sepals, united or free, according to species. The five petals of many of the species close at night. The five-locular ovary is superior, the five petal bases clawed and basally united in a tube.

There are ten stamens in two series, the smaller ones opposite the sepals, the inner five taller, opposite the petals. There are five styles ending in capitate or tufted stigmas, at yet a different height than the stamens. Style length often varies. This arrangement of stamens and stigmas minimises self-pollination. The locules of the fruit capsule dehisce separately.

The Oxalis genus comprises about 500 species of which around 270 occur in southern Africa, 120 in the fynbos, 30 in the Little Karoo and at least 20 in renosterveld. Many species occur in South America. Some species in the west of South Africa are summer dormant, appearing after autumn rains.

The leaves and stems of some species are used in flavouring stews. In some parts of the country, like Namaqualand, people eat or used to eat the corms, called uintjies. Small mammals like mole rats and porcupines also eat them, as do some francolins or spurfowls. The acidic feature of some species has been used as a vermifuge, to expel parasitic worms.

The plant in picture may be Oxalis leptocalyx photographed in the southern Richtersveld. Some sources place this species only in the Western Cape in the Porterville, Piketberg to Tulbagh and Malmesbury region, bearing rose-pink flowers. Others have it in or also in the Richtersveld.

Neither O. leptocalyx, nor the similar O. helicoides of the Richtersveld to the Western Cape is shown in the literature that was available bearing the brick-red petals with whitish bases seen in picture. The leaves in picture are longer-petioled than those of the said two species. There are no petiolules on the three leaflets.

So, the uncertainty as to the species identification of the plant in picture is shared generously, for some to overcome (Leistner, (Ed.), 2000; Curtis-Scott, et al, 2020; Vlok and Schutte-Vlok, 2015; Williamson, 2010; Manning, 2007; Van Wyk and Gericke, 2000; Andrew, 2017; iNaturalist; http://redlist.sanbi.org).