How to Identify Prosopis Glandulosa var. Torreyana

Mar 29, 2022 | Environmental Education, Gouritz Ecological Corridors Project, Gouritz Resilient Rivers

Author: Boudine Kruger | Article adapted from Ken Coetzee’s “Prosopis, a Deadly Green Cancer” 

The Honey Mesquite Tree (or Prosopis Glandulosa var. Torreyana) is an invasive species that is fast becoming one of the more threatening, invasive plant species in South Africa, putting down roots across many of our arid regions such as the Karoo and Klein Karoo. Most notably, large areas north and west of Beaufort West are now dominated by this species. This tree is the main invasive Prosopis species in South Africa, although it may also sometimes hybridise with Prosopis Velutina.

This plant, known for thriving in harsh and difficult conditions, is taking advantage of some of our country’s drought-stricken veld areas. As a result, they create a significant risk for some of our indigenous species. To solve this invasion, enough awareness must exist to motivate people to assist in the eradication of this dangerous invader. (Which is precisely why we are writing these blogs.)

Identifying the Threat.

To identify this invader, it’s crucial to know what it looks like, especially in relation to other species with which it can be confused. We know that Prosopis Glandulosa var. Torreyana is the main culprit in this invasion, but because of its hybridisation with Prosopis Velutina, it can be somewhat tricky to identify. These hybrids are just as invasive and also pose a considerable risk. Here are some ways that you can identify this tree:

Physical Description.

  • A multi-stemmed shrub or small tree.
  • It closely resembles an Acacia.
  • Up to 10m high with dense thickets.
  • Straight paired thorns.
  • Young branches have a reddish-brown colour.
  • Small yellow flowers that occur in spikes (Like a small bottlebrush).
  • It has feathery, dark green compound leaves.
  • Individual leaflets are approximately 10-20mm in length.
  • Narrow yellowish or purplish woody pods (fruits), favoured by both livestock and game.

The Prosopis tree is phreatophytic, meaning it can get its water from the saturated zone above the water table in the soil. It can withstand significant water stress because its taproot can reach deep groundwater, penetrating more than 50 meters underground. Its roots may spread up to 40 meters laterally, allowing it to use upper soil moisture and much deeper groundwater efficiently. Prosopis is said to have the world’s deepest roots of any tree. 

The Root Of The Problem.

The Prosopis is native to northeastern Mexico and the southwestern United States of America. In 1897, German settlers in South West Africa (now Namibia) first planted this plant for shade and animal feed. Dense invasions, which were difficult to control, were already a recognised threat by the 1960s. 

In South Africa, it was first planted for windbreaks and shade in Upington, from where it expanded over the Great Karoo and the Kalahari Thornveld. Prosopis is a genus of about 45 species, some of which have become a global problem. However, other Prosopis species, such as the djembe (Prosopis Africanus), are native to Africa.

Prosopis’ rapid growth in South Africa is a severe catastrophe. It’s evident that the problem isn’t being treated as effectively as it should be, putting millions of hectares of grazing rangelands, rivers, wetlands, and groundwaters at risk. A new level of awareness is required, and landowners must be instructed, assisted, and encouraged to take action in the face of new and spreading Prosopis infestations. Farmers’ associations, farmers’ unions, and the formal agricultural industry all have a significant role to play in raising awareness about the threat of the Prosopis invasion.

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