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.
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