Taxonomic Significance of Foliar Micromorphology and Their Systematic Relevance in the Genus Solanum (Solanaceae)

Abstract

Micromorphology of vegetative and reproductive plant organs is the object of research to resolve the taxonomic problems of critical species and genera. Trichomes are distributed at the surface of aerial plant parts, having various functions and are extremely variable in their presence across plant, location on plant organs, density, form, etc., and, therefore, their morphology and structure can be used as taxonomic markers in the infrageneric classification of the genus. The purpose of this investigation was to analyse the degree of differentiation in micromorphological characters between the six species and to assess the expression of these characters in individuals with intermediate macromorphology. Of the several traits on leaf surface, the stomata are perhaps the most significant from the point of view of systematics and phylogeny. Stomata that are highly characteristic of the epidermis occur in widely divergent parts of the plants including common foliage leaves. Stomatal size is an ecologically important attribute. The size, ­distribution and frequency of stomata have been recognized as species specific and these characters were used as significant parameters in the angiosperm taxonomy as well as phylogeny; qualitative and quantitative micro morphological characters, distribution and systematic relevance of both glandular and eglandular foliar trichomes using ­scanning electron microscope (SEM) in species of genus Solanum (Solanaceae) including S. melongena var. incanum, S. aculeatissimum, S. erianthum, S. macrocarpon, S. mammosum and S. virginianum were characterized. Both the abaxial and adaxial surfaces were characterized by anisocytic stomata which were more prevalent on the abaxial surface than the adaxial surface. Glandular trichomes were capitate while nonglandular trichomes were stellate with many arms or linear fingerlike. Glandular trichomes play important roles in protecting plants from biotic attack by producing ­defensive compounds. The trichomes in the family Solanaceae vary from unicellular to multicellular, conical to elongated and smooth to ridges, with or without flattened disk at the base. Glandular capitate trichomes were the most unique on leaf surfaces of the examined taxa. In summary, the variation in morphology and distribution of foliar trichomes emerged as an important supportive taxonomic tool in delimiting species of genus Solanum.