Foliar structure and mesophyll succulence of three Korean Orostachys species, O. japonicus A. Berger, O. malacophyllus Fisch., and O. sikokianus Ohwi, were examined to survey the presence of CAM in this group. Both features demonstrated that all of them were probably CAM performing species. The foliar structure of all three species was rather simple, exhibiting only epidermis, undifferentiated mesophyll, and vascular bundles. The mesophyll consisted of large water-storing cells, each containing a large central vacuole and chloroplasts in the thin peripheral cytoplasm. A well-developed intercellular space system was found in all species. In many cases, mucilaginous materials appeared in the intercellular spaces. In addition, attention was paid to the features of the vascular tissues. Paucity of vascular tissue was a general phenomenon. The arrangement of the vascular bundles differed for each species. The mesophyll succulence (Sm) is a possible indicator of CAM. This ranged from 4.65 to 7.38 for these species. This was well within the range of Sm reported for CAM plants. The anatomical implications of ecological adaptation, and a plausible evolutionary phylogeny are also discussed.
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