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Field guide to the succulent euphorbias of southern Africa, 2019:
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title page (Rolf Becker) page 4 of cover (Rolf Becker; professor of biochemistry at the University of Limpopo for 20 years; currently Dean of the Faculty of Natural Resources and Spatial Sciences at the Namibia University of Science and Technology; has been studying euphorbias for the last fifteen years)
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ResearchGate.net, October 1, 2020
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(Rolf Werner Becker; Namibia University of Science and Technology, Faculty of Natural Resources and Spatial Sciences)