The adaptative value of leaf features (indument, stomatal type, morphology of guard cells and epidermal cells, glandular mucilagene surfaces, epicuticular wax, cuticular structure, ornamentation and thickness of the cuticle, and mesophyll) of South American species of Chenopodium subg. Ambrosia is discussed. Their taxonomic and evolutionary significance in sect. Adenois are analysed. Data on the distribution and habitat of the species are given. Stomata are shown to be important characters of taxonomic and evolutionary value. This is the first time that the morphology of guard cells has been studied in the Chenopodiaceae, and a terminology for their description is proposed in the French language. The pectinized areas of the outer walls of the guard cells have not been previously reported in any family of seed plants. Obtured stomata are reported for the first time in the Chenopodiaceae. A diagram of evolutionary relationships in sect. Adenois is proposed.
Chenopodium subg. Ambrosia, Chenopodiaceae, South America, leaf anatomy, ecology, evolution