Leaf anatomy of species in some dicotyledon families as related to the C3 and C4 pathways of carbon fixation

Species in the families Amaranthaceae, Aizoaceae, Chenopodiaceae, Convolvulaceae, Euphorbiaceae, Nyctaginaceae, Portulacaceae, and Zygophyllaceae were examined for leaf anatomy typical of plants having the C4 type photosynthetic carbon fixation pathway. They are assembled by families into three groups: genera in which all species possess the specialization; genera in which some but not all species possess the specialization; and genera in which no species possess the specialization. The specialization in leaf anatomy was noted in species of 24 genera. Its presence is highly correlated with a habitat of limited water availability and (or) with a tropical origin. The carbon dioxide compensation points of nine species in the Chenopodiaceae family were measured. Low values were obtained only for those species that possess a form of specialized leaf anatomy (Atriplex confertifolia (Torr. & Frem.) Wats., A. falcata (M. E. Jones) Standl., Halogeton glomeratus (Bieb.) Meyer, Salsola kali L. var. tenuiflora Tausch.). The latter two species, having centric leaves, do not possess the more typical differential bundle sheath chlorenchyma but do possess two, individually distinct, single-cell layers of chlorenchyma, adjacent and external to the peripheral veins.