Distribution and evolution of C⁴ syndrome in Eleocharis, a sedge group inhabiting wet and aquatic environments, based on culm anatomy and carbon isotope ratios

In order to clarify the occurrence of the C₄ syndrome in Eleocharis, a group of bladeless sedges inhabiting wet and aquatic environments, the anatomical characteristics and carbon isotope ratios of culms were investigated in 118 species. Among these, only six species of the series Tenuissimae showed the Kranz type of anatomy and δ13 C values typical of C₄ plants. In spite of there being rather few C₄ species, they demonstrated anatomical variability in the structure of bundle sheaths and in the location of metaxylem vessels. In these C₄ species, E. baldwinii, E. retroflexa and E. vivipara had the characteristics of amphibious plants. On the other hand, there was an anatomical gradation from typical non-Kranz type to typical Kranz type in the genus, showing various levels of the development of vascular parenchyma cells and the radial arrangement of mesophyll cells. E. quinquangularis, E. reverchonii and E. spegazzinii possessed intermediate or Kranz-like anatomy. This genus provides a unique opportunity to study the adaptive and evolutionary aspects and the expression of C₄ syndrome.