Survey of Foliar Trichomes in Combretum Loelf. (Combretaceae) in Parts of West Africa

摘要

We studied the foliar trichome types, density and distribution among the genus Combretum Loelf. in parts of West Africa. Fresh and herbarium specimens were used. These specimens were fixed, peeled, trichome types identified and micro-photographed using a Leica WILD MPS 52 microscope camera on a Leitz Diaplan microscope. Generally, two major trichome groups were identified among these species studied. These include glandular trichomes: multicellular gland head with uniseriate stalk (MGU), cylindrical uniseriate clavate trichome (CUCT), unicellular gland with unisariate stalk (UGHU), cylindrical uniseriate trichome (CUT), paltate gland head (PGH) and combretaceous eglandular (non-glandular) conical trichome (long and short types). The eglandular trichome types were the most widely distributed trichome found in the species and could be used to distinguish the genus. They occurred in all the species studied except C. glutinosum and C. micranthum. Among the glandular trichomes, cylindrical uniseriate trichome was the most dominant occurring in 11 species namely; C. aculeatum, C. bracteatum, C. collinum subsp. binderianum, C. collinum subsp. hypopilinum, C. constrictum, C. capitatum, C. hispidum, C. nigricans, C. panuculatum, C. platypterum and C. zenkeri. This is followed by multicellular gland head with uniseriate stalk (MGU) trichome type which occurred in 9 species (C. bracteatum, C. collinum subsp. binderianum, C. collinum subsp. hypopilinum, C. constrictum, C. excelsum, C. hispidum, C. mooreanum, C. platypterum and C. racemosum). The trichome density varied from 1.25±0.44 trichomes per 100 cells to 600 trichomes per 100 cells. The distribution/occurrence, density and type of these trichomes formed dependable character for delimitating Combretum species. The findings of this study showed that trichomes provide good taxonomic characters useful for in differentiating the genus Combretum in West Africa.