Abstract: | The carbon isotope ratios (δ13C values) of samples of Kalanchoë species collected in Africa were compared with previous data obtained with species from Madagascar. In contrast to the Malagasy species which cover the whole range of δ13C values from ?10 to ? 30%o, indicating high inter- and intraspecific diversity of CAM performance, in the African species nearly all δ13C values were less negative than ?18%0. Thus, in the African species the CAM behaviour is characterized by CO2 uptake proceeding mainly during the night. The distribution of δ13C values among the species clearly mirrors the taxonomic groups and the three sections of the genus Kalanchoë sensu lato. The Kitchingia section comprises only groups having CAM with a high proportion of carbon acquisition by the C3-pathway of photosynthesis. The same holds true for the first three groups of the Bryophyllum section, whereas in the following groups of the section CAM with CO2 proceeding mainly during the night is common. The latter CAM mode is typical also for the majority of groups and species in the section Eukalanchoë. The African Kalanchoë species belong to the Eukalanchoë section, whereas in Madagascar all three sections are abundant. The data support the view that the centre of adaptive radiation of the genus is located in Madagascar. They also suggest that high CAM variability is abundant in the more primitive taxa of the genus, whereas the phylogenetically more derived taxa show a stereotype CAM with CO2 uptake taking place only during the night. |