The Blue Sour Plum Family Olacaceae (Ximenia americana)

THE blue sour plum differs from the large sour plum by having blue-green leaves, which are often folded lengthwise and recurved.

The leaves are covered with a dull blue-grey, waxy layer which may be rubbed off. The fruit is yellow to orange rather than red, less tasty than the large sour plum and turns a dark blue when dried, hence the English common name.

Names: G. Sauerpflaume; A. kleinsuurpruim; H. omuninga N/D. +eros. Ximenia: named after the Spanish monk Xaver Ximenez who described the flora of Mexico during the 17th century; americana – from America. This species occurs in Central America from California and Florida to northern Argentina and in Africa from Senegal and Sudan into the northern regions of South Africa.

The blue sour plum is a many-stemmed shrub forming dense thickets or sometimes a small tree, 2 – 3 m high. It is one of the most common woody species found from the Erongo Mountains to the northern boundary of Namibia. It grows in many different habitats but most often on sandy plains. The pale grey bark is smooth with small white flecks; young branchlets are blue-green and hairless. The straight thorns are 6 – 60 mm long. Inconspicuous greenish flowers appear from August to May, giving rise to plum-like fruit of 20 mm length from November until March. They remain on the branch for quite some time. The largish stone is covered by a layer of juicy but very sour flesh and the fruit is best eaten when overripe.

Traditionally the skin of the blue sour plum is placed on healing wounds and sores; roots, bark and leaves are also used in traditional remedies. The oil, which does not dry out, is used as body lotion and to soften leather. Some medicinal and cosmetic properties have been confirmed by scientific research and several pharmaceutical and cosmetic preparations have been patented.

Traditionally the seed oil is extracted from the kernels by roasting, crushing and boiling, resulting in a very dark and strong smelling product. Ximenia oil contains exceptionally long fatty acids and is considered of interest for the international cosmetic trade, however, the dark colour and the stickiness of the oil is a draw-back. In order to help rural communities benefit from sustainably produced indigenous natural products several NGOs worked together to develop a process by which cold-pressed ximenia oil of an acceptable quality can be produced in Windhoek.

In several areas in northern and north-western Namibia, notably Eenhana and Epembe, where the blue sour plum is plentiful, Ximenia seeds consequently form the basis of quite a profitable home industry.

Traditionally fruit trees and tree products enable women to earn some cash by collecting, drying and cracking the ximenia seeds. The nut is placed on a stone and carefully beaten with a stick to ensure that the kernel can be taken out in one piece. The kernels are then transported to Windhoek for cold-pressing and export as a cosmetic ingredient.

Studies have shown that both Ximenia species are hemi-parasites, meaning that they form specialized roots capable of penetrating and absorbing nutrients and other material from the host plant. They can even penetrate inanimate objects such as plastic, pebbles and charcoal.