Evolution of trichome and its phylogenic significance in the genus Phlomoides (Lamioideae; Lamiaceae)

Trichomes of 64 species of the genus Phlomoides representing all recognized sections and subsections were examined using stereomicroscopy and scanning electron microscopy. Trichomes provide valuable characteristics in the delimitation of sections, subsection, and species. Trichome characters of taxonomic interest were: glandular, non-glandular, branched, simple, papillate, and/or smooth on the surface. Two basic types of trichomes can be identified: non-glandular and glandular. Both trichome types can be simple or divided. Different kinds of branched trichomes were observed in most species of sect. Phlomoides, whereas the species of sect. Filipendula were mostly covered by simple trichomes. Moreover, variation in trichome characters appears to have a particular value, not only in classification at sectional or subsectional rankbut also in separating different species within a section. For example, all studied species of subsect. Fulgentes are characterized by various kinds of stellate trichomes, while the trichome variability in subsect. Tetragonae was sufficiently high for species discrimination. Following evolutionary trends are suggested here regarding trichome characters in Phlomoides: (1) long simple trichomes are derived against branched hairs, (2) multi-nodal branched trichomes are primitive against uni-nodal branched ones, and (3) presence of stalked glandular trichomes is advanced against subsessile or sessile ones

کلیدواژه ها:

Phlomoides ، Hair micromorphology ، Evolutionary trends ، Classification