Epicuticular waxes and glaucousness of Encephalartos leaves

Abstract

The epicuticular leaf waxes from four glaucous and four non-glaucous species of Encephalartos were examined by GC-mass spectrometry and SEM techniques. The four glaucous-leaved species, E. horridus, E. lehmannii, E. princeps and E. trispinosus, all occurring in xeric conditions in the Eastern Cape Province of South Africa, were conspicuous in having leaf waxes containing a series of secondary alcohols. In addition to 10-nonacosanol as the principal wax component, minor amounts of C 25C 31 10-alkanols, 4,10-, 5,10- and 7,10-nonacosanediol and the ketone, 10-nonacosanone, were detected in these species. The adaxial leaflet surfaces of the glaucous species all showed a distinctive trabecular deposit of wax platelets when viewed microscopically. By contrast, secondary alcohols and ketones were absent in waxes from the non-glaucous species, and the surface of leaflets of these taxa were relatively featureless microscopically. Varying quantities of alkanes, fatty acids, primary alcohols, aldehydes and alkyl esters were present in all samples. Amongst the non-glaucous species, E. altensteinii, E. natalensis and E. woodii were similar in their wax composition, but differed from E. villosus. Alkanes were dominant in the latter species, which had high proportions of hentriacontane and tritriacontane in parallel with the most prominent oxygenated wax compounds, C 32 and C 34 fatty acids and aldehydes.