Beschreibung:
Abstract C₄ photosynthesis independently evolved >62 times, with the majority of origins within 16 dicot families. One origin occurs in the poorly studied genusAnticharisEndl. (Scrophulariaceae), which consists of ∼10 species from arid regions of Africa and southwest Asia. Here, the photosynthetic pathway of 10Anticharisspecies and one species from each of the sister generaAptosimumandPeliostomumwas identified using carbon isotope ratios (δ13C). The photosynthetic pathway was then mapped onto an internal transcribed spacer (ITS) phylogeny ofAnticharisand its sister genera. Leaf anatomy was examined for nineAnticharisspecies and plants fromAptosimumandPeliostomum. Leaf ultrastructure, gas exchange, and enzyme distributions were assessed inAnticharis glandulosacollected in SE Iran. The results demonstrate that C₃ photosynthesis is the ancestral condition, with C₄ photosynthesis occurring in one clade containing four species. C₄Anticharisspecies exhibit the atriplicoid type of C₄ leaf anatomy and the NAD-malic enzyme biochemical subtype. SixAnticharisspecies had C₃ or C₃–C₄ δ13C values and branched at phylogenetic nodes that were sister to the C₄ clade. The rest ofAnticharisspecies had enlarged bundle sheath cells, close vein spacing, and clusters of chloroplasts along the centripetal (inner) bundle sheath walls. These traits indicate that basal-branchingAnticharisspecies are evolutionary intermediates between the C₃ and C₄ conditions.Anticharisappears to be an important new group in which to study the dynamics of C₄ evolution.