Prosopis (Prosopis chilensis & Prosopis spp.)

LUISE HOFFMANNPROSOPIS is not indigenous to Namibia but is included in this series since it is so very common and highly invasive in our country.

Prosopis chilensis was imported to what was then South West Africa in 1912 by the German botanist Kurt Dinter to provide shade and fodder in the arid southern parts of the country.

Various subspecies of prosopis, in particular P. glandulosa, were accidentally introduced with horse feed. Hybridising easily, they become highly invasive especially along dry water courses all over the country from Outjo southwards where they out compete the indigenous camel thon (Acacia erioloba) and sweet thorn (A. karroo).

It is a multi stemmed tree, usually branching from the base and 5 – 18 m high, the branches growing erect at first and then bending outwards, or forming spiny and shrubby impenetrable thickets especially in the Auob and Nossob Rivers.

In September October the prosopis is very visible because its bright green feathery leaves appear while the remaining vegetation is still dry and grey. The leaves are twice compound with 2 4 pinnae, the leaflets much bigger and the pinnae much longer than those of our acacias.

Young branches are smooth and shiny reddish brown with very sharp, strong spines of the same colour growing in pairs. The prick of the spines is particularly painful and they are lethal to tyres.

Names: E. Honey locust, mesquite; A. Soetpeul, Suidwesdoring; N/D. /narab Afrikaans bdquo;soetpeul “, meaning bdquo;sweet pod “, refers to the sweet and nourishing pith of the pods. “Suidwesdoring ” or “southwest thorn ” refers to the former name of Namibia, indicating that this tree is very common in the country.

Another name commonly used in southern Africa is Algarroba. However, that name is also used for the carob tree (Ceratonia siliqua) hailing from the Mediterranean regions, which is as hardy and nutritious as the prosopis but not invasive.

Pale yellow flower spikes appear in October hanging from quite a length of the branches, unlike those of our acacias, which usually flower at the tips of the branches. They produce copious amounts of pollen to which many people are highly allergic.

The pods are brownish yellow to purple, up to 20 cm long and the seeds are embedded in a sweet, floury pith.

Prosopis is a threat to biodiversity, to farming and to tourism by creating impenetrable thorny thickets, depriving local vegetation of water and space and by e.g. invading the banks of the Orange River, already making it difficult for participants of popular boat trips to find suitable spots to camp.

The Windhoek municipality destroys prosopis chemically because of its allergenic pollen and because the roots are highly aggressive, invading drain pipes through the tiniest crevices and clogging them. This tree should not be planted anywhere and all young seedlings must be removed immediately.

In the south western United States, this tree’s country of origin, prosopis, known as “mesquite “, has invaded 28 million ha of former productive grazing and is known as “the tree too tough to kill “.

The tree provides good fire wood and the wood is used for high quality furniture and flooring.