An altitudinal survey of grasses and sedges was conducted on the Sirimon and Chogoria tracks on Mount Kenya to supplement previous surveys restricted to the Timau track. Thirty seven grasses and twenty three sedges were recorded and stable carbon isotope analysis was used to identify the photosynthetic pathway (C3 or C4) used by these species. The occurrence of a group of C4 graminoids was confirmed close above the tree line, and the literature suggests this may also hold for the Aberdares Range and other East African mountain massifs. Lower altitude graminoids are C3 forest species, and this distribution upsets the assumption that C4 gives way to C3 with increasing altitude. The significance of this is discussed in relation to the interpretation of palaeoenvironments through carbon stable isotope proxies.
