In regard to its flora the country may be divided into (1) the northern plain sloping from the Balkans to the Danube, (2) the southern plain between the Balkans and Rhodope, (3) the districts adjoining the Black Sea, (4) the elevated basins of Sofia, Samakov and Kiustendil, (5) the Alpine and sub-Alpine regions of the Balkans and the southern mountain group. In the first-mentioned region the vegetation resembles that of the Russian and Rumanian steppes; in the spring the country is adorned with the flowers of the crocus, orchis, iris, tulip and other bulbous plants, which in summer give way to tall grasses, umbelliferous growths, dianthi, astragali, etc. In the more sheltered district south of the Balkans the richer vegetation recalls that of the neighbourhood of Constantinople and the adjacent parts of Asia Minor. On the Black Sea coast many types of the Crimean, Transcaucasian and even the Mediterranean flora present themselves. The plateaus of Sofia and Samakov furnish specimens of sub-alpine plants, while the vine disappears; the hollow of Kiustendil, owing to its southerly aspect, affords the vegetation of the Macedonian valleys.
The flora of the Balkans corresponds with that of the Carpathians; the Rila and Rhodope group is rich in purely indigenous types combined with those of the central European Alps and the mountains of Asia Minor. The Alpine types are often represented by variants: e.g. the Campanula alpina by the Campanula orbelica, the Primula farinosa by the Primula frondosa and P. exigua, the Gentiana germanica by the Gentiana bulgarica, etc. The southern mountain group, in common, perhaps, with the unexplored highlands of Macedonia, presents many isolated types, unknown elsewhere in Europe, and in some cases corresponding with those of the Caucasus. Among the more characteristic genera of the Bulgarian flora are the following: - Centaurea, Cirsium, Linaria, Scrophularia, Verbascum, Dianthus, Silene, Trifolium, Euphorbia, Cytisus, Astragalus, Ornithogalum, Allium, Crocus, Iris, Thymus, Umbellifera, Sedum, Hypericum, Scabiosa, Ranunculus, Orchis, Ophrys.
The principal forest trees are the oak, beech, ash, elm, walnut, cornel, poplar, pine and juniper. The oak is universal in the thickets, but large specimens are now rarely found. Magnificent forests of beech clothe the valleys of the higher Balkans and the Rilska Planina; the northern declivity of the Balkans is, in general, well wooded, but the southern slope is bare. The walnut and chestnut are mainly confined to eastern Rumelia. Conifers (Pinus silvestris, Picea excelsa, Pinus laricis, Pinus mughus) are rare in the Balkans, but abundant in the higher regions of the southern mountain group, where the Pinus peuce, otherwise peculiar to the Himalayas, also flourishes. The wild lilac forms a beautiful feature in the spring landscape. Wild fruit trees, such as the apple, pear and plum, are common. The vast forests of the middle ages disappeared under the supine Turkish administration, which took no measures for their protection, and even destroyed the woods in the neighbourhood of towns and highways in order to deprive brigands of shelter. A law passed in 1889 prohibits disforesting, limits the right of cutting timber, and places the state forests under the control of inspectors.
According to official statistics, 11,640 sq. m. or about 30% of the whole superficies of the kingdom, are under forest, but the greater portion of this area is covered only by brushwood and scrub. The beautiful forests of the Rila district are rapidly disappearing under exploitation.