Micromorphological and chemical characteristics of cuticular waxes of Cleistes (Orchidaceae, Pogonieae)

Abstract

Micromorphology of cuticular waxes of leaves of 13 species of South American Cleistes Rich. ex Lindl. (Vanilloideae: Pogonieae) were observed by scanning electron microscopy. Chemical constituents of the waxes of eleven species were identified by gas chromatography. The observations were carried out with individuals of native populations occurring in South, Southeastern, Northeastern and Central-Western Brazil. The micromorphology of the cuticular waxes varied from amorphous deposits to parallel stacked platelets. The latter morphological pattern seems to be more common in plants from dryer habitats. Alkyl acids are predominant constituents of waxes of most species. Alkyl alcohols predominate in other species and alkanes are predominant in only one of the studied species. Alkyl esters, monoglycerides and sterols are minor compounds, having not been detected in some species. Either hexadecanoic or octadecanoic are main homologues of alkyl acids; regarding alkyl alcohol homologue distribution, hexacosanol, octacosanol and triacontanol predominates; pentacosane, heptacosane, octacosane, nonacosane and hentriacontane predominate in alkane homologue distributions. No correlation exists between chemical composition and micromorphology of the wax deposits. Stomata distribution restricted to the adaxial or on both foliar surfaces, morphology of wax deposits and chemical composition do not correlate with molecular phylogeny. On the other hand, all these attributes may be useful for species characterization and distinction between species.