IN September each year, South Africa’s Gauteng province turns purple. The cities of Johannesburg and Pretoria are well covered with trees – and jacarandas (Jacaranda mimosifolia), with their purple blooms in late spring, are a prominent part of this urban forest. JENNIFER FITCHETT, Associate Professor of Physical Geography, University of the Witwatersrand About 16% of the land in the Gauteng City Region is planted with trees, forming one of the world’s largest and most densely vegetated man-made urban forests. Johannesburg alone is recorded to have over 10 million trees. Jacarandas were introduced to Pretoria and later Johannesburg in the early…