Grown-up trees of C. rosea (girths larger than 7 cm, heights taller than 2 m) in the Virgin Islands have a strong component of nocturnal CAM-type CO2 fixation as indicated by their δ 13 C values of ≈ −18‰ reaching up to the low end of the range typical for CAM (−9 to −18‰). Seedlings (girths up to 3.5em and heights up to 1.2m) have a smaller but still notable CO 2 -dark fixation as suggested by ODC values of ≈ −21 to ≈ −26‰, and only very small seedlings appear to be exclusively C 3 (δ13C = −29‰). The larger variation of δ 13 C-values among seedlings suggests that seedlings make more flexible use of the options of CO 2 dark- and light-fixation than adult trees, while the larger variation of δD-values among trees supports the conclusion, that overall the trees are more flexible in their use of water in transpiration. More negative values of δ 13 C and δD in terrestrial plants as compared to their epiphytic sympatriotes suggest that the ratio of dark fixation to light fixation of CO 2 is smaller in terrestrial plants and that epiphytic plants transpire more of the water available to them. Leaf-N levels support the assumption of a better supply of the terrestrial plants. The analyses of stable isotopes and leaf-N levels, which are very suitable for screening in the field, corroborate the high ecophysiological flexibility of C. rosea as shown by more elaborate experimental approaches in the laboratory and in the field.