The foliar trichomes of Combretum apiculatum subsp. apiculatum (Combretaceae): Morphoanatomy and histochemistry

Abstract

Combretum apiculatum Sond. subsp. apiculatum is an important plant used in the traditional medicinal treatment of many diseases including gastrointestinal disorders, conjunctivitis, aches and leprosy. The plant's medicinal properties are putatively associated with secondary metabolites present in trichomes found on the leaf surfaces. This study aimed to investigate the distribution and morphology of the glandular trichomes of C. apiculatum at various stages of leaf development (emergent, young and mature) using stereo-, compound-light- and scanning electron microscopy, as well as to determine the leaf phytochemical constituents and to correlate the plant's medicinal properties at the cellular level by histochemical analyses. The microscopical studies revealed multicellular subsessile/sessile peltate, glandular trichomes and unicellular to multicellular non-glandular trichomes at all leaf developmental stages. Emergent leaves consisted of dense distributions of trichomes located in epidermal depressions, suggesting emergence during the early stages of leaf development. Trichome density decreased with leaf maturation, potentially attributable to the leaf expansion theory. Histochemical analyses on the leaves and trichomes detected alkaloids, phenolic compounds, lignin, terpenoids, resin acids, pectins, mucilage, carboxylated and hydroxylated polysaccharides, polyphenols, total lipids, total proteins and nucleic acids, indicating cell viability. These compounds possess medicinal properties, thereby providing supporting evidence for the plant's traditional medical use.