Anatomy of Succulence and CAM in 15 Species of Senecio

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Abstract
The ability of some species of the genus Senecio to perform Crassulacean acid metabolism (CAM) in plants growing both under controlled conditions and outdoors and the anatomy of their photosynthesizing organs, leaves, and/or stems were investigated. The studies species differed in leaf morphology and in degrees of leaf and stem succulence. Malate accumulaton differed with enviromental conditions. The carbon isotope ratio .delta.13C indicated that, in most of the species, the C3 carboxylation pathway was operating, although malate fluctuations indicated that CAM cycling occurred. In some species, carbon isotope ratios ranged between C3 and C4 values, indicating switching of photosynthetic pathways. Only two leafless species that were apparently obligate CAM species had a .delta.13C typical of plants assimilating CO2 through the phosphoenolpyruvate carboxylase pathway.