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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.

The current study presents data about the diversity and ecology of filamentous blue-green algae, found in the phytoplankton of 42 standing water basins in Bulgaria. We identified 9 species from Cyanoprokaryota, which belong to 5 genera from order Nostocales. Ecological characterization of the identified species has been performed. Data about the physicochemical parameters of the water basins are also provided.

This study reports data on the diversity of Pteridophyte of the “Bulgarka” Nature Park. Twenty-nine species belonging to the divisions Lycopodiophyta, Equisetophyta and Polypodiophyta were identified, including six new species to the park: Asplenium onopteris, Dryopteris dilatata, Equisetum palustre, Huperzia selago, Ophioglossum vulgatum and Polystichum lonchitis. Among the identified species the ferns were prevailing. Fifteen species were medicinal plants and eight species have conservation significance. The status of the populations and major threats to the habitats were discussed.