Meet the Trees of Namibia … Rock tannin-bush (Osyris lanceolata)

• Luise HoffmannTHE most obvious properties of this plant are its occurrence on rocky outcrops and hill slopes and the leaf stalks that run down along the stem and form ridges causing the stem to appear angular.

Names: G. Rindenbusch; A. bergbas; rotslooibos; H. ombahu. The generic name Osyris is derived from the Greek word ‘ozos’ meaning branch and refers to the branching habit of the shrubby tree, while the specific name lanceolata indicates the lance shape of the leaves. The bark and the leaves are very rich in tannin and have been used for tanning, hence the English and Afrikaans common names.

This uncommon to rare tree belongs to the sandalwood family (Santalaceae). Members of this family often are hemi-parasites meaning that they utilise the root systems of other plants from which they derive water and nutrients. However, unlike true parasites, which extract all their nutrient requirements from their host plant, they have green leaves by means of which they convert the energy of the sun into sugars that are stored in the plant for later use.

In the process, like all green plants, they also release oxygen into the air, which is vital to the majority of living beings.

In Namibia the rock tannin bush occurs widespread but scattered. It is mostly found on rocky outcrops and hillslopes where it often grows in close contact with other woody species. But it also grows directly on rocks. Its parasitic nature has not yet been clearly established.

According to the Namibia Tree Atlas it is mostly a shrubby tree of up to three metres but there are also records of between three and eight metres. It does not seem to be very common anywhere but it may have been overlooked due to its preference for growing on less accessible places and often in other shrubs.

The rock tannin-bush also occurs naturally in rocky places from the Eastern Cape northwards through the eastern half of South Africa and as far north as Ethiopia.

Its stiff, blue-green leaves are evergreen, smooth, thick and leathery and end in a sharp point. They are usually covered in a waxy layer, a feature found in many plants in arid regions because it reduces evaporation.

Male and female flowers grow on separate plants. They are very small, yellow-green and develop into fleshy stone-fruit, measuring about 1,5 x 1 cm and crowned by the persistent remains of the flower. Elliptic to almost ball-shaped, they are red to dark purple when ripe.

In Namibia the bark is pulverised and rubbed into incision above rheumatic or arthritic joints to alleviate pain. Taken internally, the powdered root is also used to treat diarrhoea since tannins have anti-inflammatory properties. In east Africa the root is known as a diuretic. In northern Africa the wood is also used as a substitute for sandalwood (Santalum album).

The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of red wine, strong tea, or an unripe fruit. Due to its astringent nature the powdered bark can also be used to stop bleeding.

Tannins are usually found in large quantities in the bark of trees where they act as a barrier for micro-organisms and protect the tree.

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