ABSTRACT

The halophytic genus Suaeda (Chenopodiaceae) includes species with the C₃ and C₄ photosynthetic pathways.  North American species of this genus were investigated to determine whether C₃ and C₄ 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 C₃ anatomy, whereas all species from section Limbogermen were found to be C₄ species.  Characteristics of leaf anatomy and chloroplast ultrastructure are similar to those reported from C₃ and C₄ 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 ( d¹³C) of above –20.  All species from section Chenopodina have austrobassioid leaf anatomy without a chlorenchymatous sheath and d¹³C 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 C₃ and C₄ photosynthetic syndromes are with few exceptions distributed along sectional or subsectional lines.  These findings throw new light on the infrageneric taxonomy of this genus.

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