Photosynthetic pathways and ecological distribution ofEuphorbia species in Egypt.

The photosynthetic pathways of 42 species of the genusEuphorbia growing wild, naturalized or cultivated in Egypt were investigated. The criteria used included the δ13C- and δD-values and Kranz anatomy of the leaves. There is a relationship between the photosynthetic pathway and the ecological conditions in the habitat of a particular species. All 4 CAM species are succulent shrubs, wild or cultivated. The 11 species with C4 pathways are mainly summer annuals of tropical origin and flourish under the hot summer conditions. The 27 C3 species are either winter annuals, perennials, perennials flourishing in winter or shrubs; the majority are Mediterranean, European or Saharo-Arabian. Summer annuals with C3 pathways grow under the shade of the summer crops. Generally, C3 plants grow under conditions of relatively better water resources and lower temperature than the C4 plants. The majority of the CAM and C4 species occur in the southern part of the country, where high temperature is a common feature of the climate.