Micromorphological studies on nutlet and leaf indumentum of genus Teucrium L. (Lamiaceae) in Iran

The micromorphology of leaf indumentum and nutlet surface of 12 species belonging to the 6 sections of the genus Teucrium L. was studied by scanning electron microscope (SEM). Eight types of trichomes are identified including unbranched unicellular trichomes, unbranched multicellular trichomes, sessile glands, subsessile glands, stalked-multicellular glands long clavate glandular trichomes (with 3-5 cells), trichomes with large thin-wall, trichomes with non-micropapillate basal cell, which are the most general types on the adaxial side of the leaves, and branched trichome with long axis is the exclusive type and present in Teucrium polium L. Thus, trichomes can be used as a distinctive taxonomic character in species classification. Nutlet shapes in most species are elliptic-ovate, the surface of which is polygonal with different ornamentations and wall thickness, and the indumentum varies in different species, but it has some significant similarities within the sections. The absence or presence of the indumentum and its different types has high taxonomical values among the species.