The Thracian Plain, between the Sredna Gora and the Rodopi, originally featured a mixture of midlatitude forest and Mediterranean flora. The forests have been removed from the level lands and have been replaced by a diversification of crops, including truck vegetables, fruit orchards, strawberries, raspberries, vineyards, tobacco, and cotton. The plain also produces a variety of herbs and medicine derivatives. Digitalis is produced from foxgloves; menthol, from peppermint; opium, from a species of poppy; linseed oil, from flaxseed; laxatives, from iris and rhubarb; and castor oil, from the castor bean. All of them are grown on this plain.
Where the plain touches the Black Sea, varieties of tropical or subtropical vegetation appear. Vegetation is dense along the Kamchiya River and on the banks of a few of the smaller streams as they approach the sea. Reeds, lianas, exotic flowers, and huge old trees that grow nowhere else in the country flourish in this region.
In the southern Rodopi, where a few of the river valleys--those of the Struma, Mesta, and Maritsa, for example--open to the south, the vegetation is typically Mediterranean. Natural species include the Mediterranean scrubby underbrush, maquis, and an assortment of flowering plants and shrubs. Vineyards and subtropical fruit grow well in these valleys. Such areas produce the country's peaches, figs, and peanuts.
Mountainous regions feature Alpine meadows and pastures above the tree line, where the terrain permits, and conifer forests immediately below the tree line. Deciduous trees are native to all of the uplands of the country with tolerable elevations. Beech predominates at intermediate elevations, particularly on northern slopes, and oak, on the lower foothills. There are dense elm, oak, and ash forests at lower elevations in the Kamchiya River valley where it descends from the eastern part of the Stara Planina. Scrub and brush prevail at all upland elevations where terrain and soil conditions are poor or where the original forest has been removed and has not been replaced.
The Stara Planina has grassy meadowland and pastures on rounded summits and higher slopes. In the springtime these higher lands may also be brilliant with wild flowers and flowering shrubs. Cherry laurel, for example, grows wild over wide areas. The meadows usually give way to beech and to other mixed deciduous forests at lower elevations. Mixed forests may contain varieties of oak, chestnut, hornbeam, elm, and ash.