ABSTRACT
In studying the mountain flora of Central Africa, one is struck by the similarities found in mountainous massifs often separated by considerable distances. This inevitably implies a common origin, which must be located in time and space. Particularly in the Congolese mountains, the phytogeographic interest revealed by the Ruwenzori—which is, except for the adjacent Virunga, very isolated in relation to the other massifs of comparable altitude—must be stressed. As to the exogenous hypsophilic species, of extratropical origin, their introduction could occur only under two conditions: if the mountains had attained a sufficient altitude, and if there were vacant habitats ready to receive them. The scheme outlined here, therefore, supposes the existence on the East African plateau, in the Tertiary, of a relatively mesophilic climate, permitting the old submontane flora (with Lobelia) to coexist with the hygrophilic forest flora. The climate would have progressively dried and warmed while the mountains built up.
