Beyond the Scent: New Evidence about Micromorphological, Phytochemical and Biological Features of Plumeria rubra ‘Tonda Palermitana’ (Apocynaceae)

Plumeria rubra L. is an ornamental Caribbean plant widely known for its ethnobotanical uses and pharmacological activities. The ‘Tonda Palermitana’ cultivar, on which no data are to date available, is commonly cultivated in Sicily. The aim of our study was to characterize the micro-morphological features of leaves and flowers of this cultivar by light and Scanning Electron Microscopy and to investigate the phytochemical profile and the biological properties of their foodgrade extracts (LE and FE, respectively) by LC-DAD-ESI-MS analysis and different in vitro assays. Numerous branched laticifers were observed, and their secretion contained alkaloids and lipophilic compounds as confirmed by histological analyses. Phytochemical analyses showed the presence of alkaloids (9%), terpenoids (13%) and fatty acids (6%), together with a very abundant presence of iridoids (28%) and polyphenols (39%). The most notable biological activity of both extracts appears to be the antioxidant one, showing half-inhibitory concentrations (IC50) about 5 times lower than those detected in anti-inflammatory assays (383.74 ± 5.65 and 232.05 ± 2.87 vs. 1981.23 ± 12.82 and 1215.13 ± 10.15, for FE and LE, respectively), with LE showing the best, and statistically significant (p < 0.001), biological activity. These results allow us to speculate promising nutraceutical and cosmeceutical applications for this old Sicilian cultivar.