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The halophytic genus Suaeda (Chenopodiaceae) includes species with the C-3 and C-4 photosynthetic pathways. North American species of this genus were investigated to determine whether C-3 and C-4 leaf anatomy are consistent within the two sections of Suaeda, Chenopodina and Limbogermen, present on this continent. All species from section Chenopodina were found to possess C-3 anatomy, whereas all species from section Limbogermen were found to he C-4 species, Characteristics of leaf anatomy and chloroplast ultrastructure are similar to those reported from C-3 and C-4 species. respectively, from the Eastern Hemisphere. All species from section Limbogermen have the suaedoid type of leaf anatomy, characterized by differentiation of the mesophyll into palisade parenchyma and a chlorenchymatous sheath surrounding central water-storage tissue, as well as leaf carbon isotope ratios (delta(13)C) of above -20. All species from section Chenopodina have austrobassioid leaf anatomy without a chlorenchymatous sheath and delta(13)C values of below -20. According to our literature review, the photosynthetic pathway has now been reported for about half (44) of the Suaeda species worldwide. The C-3 and C-4 photosynthetic syndromes are with few exceptions distributed along sectional or subsectional lines. These findings throw new light on the infrageneric taxonomy of this genus.