E. S. Martins & J. R. Timberlake 
Flora Zambesiaca Volume 8 Part 8 [PDF ebook] 
Labiatae, Pogostemonoideae to Nepetoideae Tribe Mentheae

The Flora Zambesiaca series, published in more than two hundred parts, provides comprehensive descriptive accounts of the flowering plants and ferns native and naturalized in Zambia, Malawi, Mozambique, Zimbabwe, Botswana, and the Caprivi Strip. Meticulous botanical illustrations illustrate an example of each genera. An essential tool for ecological surveys, as no other publication provides the depth and scope. Published in paperback following a modified Bentham & Hooker system, as parts or as whole volumes as and when they are complete.