Ultrastructure and carbon isotope ratios of leaves in c₄ species of Rhynchospora (Cyperaceae) that differ in the location of Kranz cells

The genus Rhynchospora in the Cyperaceae includes both C₃ and C₄ species. The C₄ species shows two distinct Kranz anatomies: the rhynchosporoid and the fimbristyloid-chlorocyperoid intermediate. This study reports the use of herbarium specimens to obtain the leaf ultrastructure in eight Rhynchospora C₄ species in relation to their C₄ biochemical subtypes, together with carbon isotope ratios. Despite the use of dried materials, electron microscopic observation revealed the structures of chloroplasts and cell walls. In C₄ species with the fimbristyloid-chlorocyperoid intermediate anatomy, Kranz cell chloroplasts had reduced grana and convoluted thylakoids, and suberized lamellae occurred in the mestome sheath cell walls. In C₄ species with the rhynchosporoid anatomy, the Kranz cell chloroplasts also had reduced grana and convoluted thylakoids but with less convolution; suberized lamellae occurred in the Kranz cell walls. These data show that the Rhynchospora C₄ species have ultrastructural features present in the NADP-malic enzyme-type C₄ sedges. The Kranz species had δ¹³C values typical of C₄ plants, as expected, and the values did not differ significantly between the two Kranz anatomies. This study demonstrates that dried herbarium specimens can be used for ultrastructural observation of C₄ leaves and provide valuable information for understanding of the photosynthetic diversity.