Micromorphological variations of trichomes in the genus Ocimum L.

Ocimum L. is an attractive fragrant ornamental plant with medicinal aromatic compounds. The study using digital microscopy revealed the distinct epidermal trichome morphology in five species of Ocimum including O. americanum L., O. basilicum L., O. gratissimum L., O. kilimandscharicum Gurke and O. tenuiflorum L. A distinguished variation in size, shape, type and abundance of trichomes on leaves and stem of all species are described and photographed. Both glandular and non-glandular trichomes scrutinized in all the species in which glandular type comprised capitate and peltate trichomes. On the stem, the longest glandular capitate trichome (GCT) and non-glandular trichome (NGT) were observed in O. tenuiflorum while O. basilicum possessed longest glandular peltate trichome (GPT). In case of foliar trichomes, the longest GCT observed on leaves of O. americanum; and O. basilicum showed the longest GPT and NGT. In the species, the septate or aseptate NGT possessed uni, bi or multicellular base with acute or broad apex. A distinguished variation in the number of cells in stalk and head of GT was observed in the study. Presence of silica bodies in peltate trichome of O. kilimandscharicum was noticed as the characteristic feature. Among the five species, the trichomes were abundant in O. kilimandscharicum; while O. basilicum showed sparse distribution. Trichomes with disrupted cells were also noted in O. americanum. Due to the presence of specific trichome characteristics, the efficient taxonomic key is prepared to identify the taxa at species level.