Anatomical characterization of Strobilanthes (Acanthaceae) species from the northern Western Ghats of India and its implication in identification at vegetative state

Abstract

A comprehensive study of stem, leaf and petiole anatomy of Strobilanthes from northern Western Ghats of India was carried out to identify characteristics which would enable species identification when flowering material was unavailable. In Strobilanthes, some species bloom annually, others are plietesials, i.e. they grow without blooming for several years and then produce huge quantities of flowers, release seeds and die. Therefore, alternative methods, such as anatomical characters, became essential to distinguish Strobilanthes species in their vegetative stage. During the study, ten species of Strobilanthes were collected from northern Western Ghats of India for anatomical characterization. Under the bright-field microscope, stem cross-sections of different species were noted as undulate, quadrangular, quadrangular-winged or terete. Study of the stem revealed a distinct outer and inner cortex, the distribution of cystoliths (CaCO sub(3) crystals), raphides (CaC sub(2) H sub(2) O sub(5) crystals), and sclereids which varied from species to species. Study of leaf anatomy showed structural variation and varied vascular bundle shapes between the species. Leaf epidermal characters under light and scanning electron microscopy exhibited variation in characters such as stomatal index, stomatal length and width, stomatal type and glandular or non-glandular trichomes. The petiole anatomy was distinct especially with respect to vascular bundle structure between species and distribution of structures such as sclereids, cystoliths, sphaeraphides and tannin cells varied. Hence, unique anatomical features of the stem, leaf and petiole could be used as taxonomic characters to identify Strobilanthes species in a vegetative state.