δ13C values of grass species collected in the northern Sahara desert.

δ13C values were measured for 45 Poaceae species collected in the northern Sahara desert, at the foot of the Saharan Atlas. The results indicate a clear relationship between carbon isotope discrimination and phytogeographical distribution of the grasses. Mediterranean species predominantly had δ13C values indicating the C3 pathway of photosynthesis. By contrast, nearly all species belonging to the Saharo-Arabian and /or Sudanian group showed a C4 like carbon isotope composition. Leaf material of two species, Lygeum spartum and Stipa tenacissima, had δ13C values in the region of-20‰, i.e. intermediate between the mean δ13C values of C3 and C4 plants. However, additional speciments of both these grasses obtained from a different source (herbarium of the Hebrew University, Jerusalem) yielded a C3 like carbon isotope composition.