XVI International Botanical Congess

Species of the family Chenopodiaceae have been subjects for studies on the carboxylation pathways (C3 and C4) because the order Caryophyllales has four carboxylation variants (C3, C4 NADME, C4 NADPME and CAM) with the Chenopodiaceae having the first three of these. The grasses are the only other group to show similar variation but with CAM absent and C4 PCK present. As elsewhere, the carboxylation variants of the Caryophyllales are correlated with anatomical and ultrastructural characters. The distribution of the C4 carboxylation syndrome in the Caryophyllales is examined. The anatomical and ultrastructural variations associated with the carboxylation pathways in the Chenopodiaceae are described and examined in detail. Various proposed classifications of and within the family are examined in relation to the anatomical and ultrastructural characteristics. It is concluded that while the characteristics of the various carboxylation pathways help in understanding some relationships, our current knowledge leaves almost as many problems as answers.