Leaf and stem anatomy of Bulgarian endemic Marrubium frivaldskyanum Boiss. (Lamiaceae)

In the Bulgarian flora, the genus Marrubium L. is represented by four species, of which M. frivaldskyanum is a rare species and Bulgarian endemic. The study presents information about the anatomy of leaves and stems of M. frivaldskyanum, collected from the floristic region of the Rhodopes Mts (western). The leaves show bifacial structure, with mesophyll which is differentiated as palisade and spongy parenchyma. The stomata are of anomocytic and diacytic types, located primarily on the abaxial epidermis. The leaf and stem surfaces are covered with two types of trichomes: non-glandular (unicellular and multicellular) and glandular. The cross-section of the stem represents the typical anatomy structure of dicotyledons. In terms of the shape, it is quadrangular, and collenchyma tissue can be seen under the epidermis in the area of the edges.