High altitude profoundly influenced plant diversity and distribution on mountains of southern Sinai (Egypt). Plants exhibiting the C3-mode of photosynthesis were widely distributed along the altitudinal transect. Plants exhibiting the C4-mode were restricted below an altitude of about 1400 m above sea level. The transition from C3-dominated areas to C4-dominated areas occurred between 1200 and 1400 m a.s.l. and O. H. Sayed, M. K. Mohamed.