the plant species that are characteristic of mountain regions. The species and especially the genus composition of mountain flora is usually poorer than that of lowland areas (with the exception of the flora of mountains near deserts). According to the altitude-zone principle, mountain flora may be divided into the so-called midmoun-tain, or montane, flora, occupying the slopes below timber-line, and the high-mountain flora (alpine in the broad sense), found above this boundary. All mountain flora is genetically linked with the surrounding flora and therefore is treated as an integral part of the same botanical-geographical region as that occupied by the flora of the lowlands. There are well-developed links between the flora of various mountain regions owing to the similar conditions of their development and to the history of plant dispersal.
The high-mountain flora of the nontropical part of the northern hemisphere is characterized by a predominance of low shrubs and bushes and especially of perennial herbaceous plants, many of which form a dense turf. Abundantly represented, especially in the mountains of Asia, are the families Gramineae, Cyperaceae, Ranunculaceae, Cruciferae, Compositae, Saxifragaceae, and Primulaceae. Montane flora is characterized by a limited variety of ligneous species: on the higher slopes there are mainly coniferous trees, such as firs and spruces, and on the lower levels there grow representatives of the Fagaceae, Juglandaceae, Aceraceae, and other families. In the arid regions of the Mediterranean (including Middle Asia) there is an abundance of perennial herbs and shrubs belonging to the families Compositae, Leguminosae, Gramineae, and Labiatae and of ligneous plants of the order Rosales, such as the (hawthorn, rose, and shadbush).
In the equatorial belt the greatest variety of ligneous species may be found in tropical rain forests, and a somewhat smaller selection of these species occurs among midmountain flora (forests in the fog belt). Epiphytes are abundant in the equatorial belt, especially mosses, small ferns, and arborescent ferns. Higher up the mountain slopes the typical tropical genera are joined by species of Juglandaceae and Fagaceae, and here ericaceous shrubs are widespread. The high-mountain regions are characterized by turf-forming perennial herbs and “columnar” ligneous forms of the families Compositae, Campanulaceae, and Leguminosae.
REFERENCESVul’f, E. V. Istoricheskaia geografiia rastenii. Istoriia flor zemnogo shara.Moscow-Leningrad, 1944.
Tolmachev, A. I. “O proiskhozhdenii nekotorykh osnovynkh elementov vysokogornykh flor Severnogo polushariia.” In the collection Materialy po istorii flory i rastitel’nosti SSSR,no. 3. Moscow, 1958.
A. I. TOLMACHEV