The occurrence of triterpenoids from Euphorbia gummifera inside the fairy circles of Garub in the southern Namibian pro-desert

The cause and maintenance of the fairy circle phenomenon of the Namibian pro-desert have not yet been satisfactorily explained. Several diverse hypotheses have been put forward, but none have universally been accepted. In the current study a possible link between the barren patches (fairy circles) of the Garub region (southern Namibian pro-desert) and Euphorbia gummifera was investigated, by determining if a characteristic compound(s) from this poisonous plant is present inside the fairy circles. With the use of GCMS trace analysis it was possible to identify euphol, a characteristic triterpenoid of the Euphorbia genus, in substantial quantities in 19 out of 20 soil samples from inside fairy circles in the Garub region. Only trace amounts of euphol could be found in 3 of 20 samples from outside the fairy circles. This implies that E. gummifera was present where there are now fairy circles. A comparison of the size of the fairy circles and E. gummifera found within the same area (Garub) additionally linked the barren patches to E. gummifera. The circles in this area have an average diameter of 3.53 m and the plants 3.44 m. This study partially supports the first published hypothesis by Theron in 1979, that the fairy circles are caused by Euphorbia spp. or their remains.