the historically formed aggregate of plant species unique to a definite geographic area owing to present natural conditions and to the geological past. The flora of one region is in more or less stable relationship with the flora of other, especially adjacent, regions. Theoretically the term “flora” embraces all the plants of a given territory, but in practice it often refers only to seed plants and ferns of the area being studied. Aggregates of lower and other higher plants are usually given such designations as the flora of spore plants, the flora of algae, and the flora of mosses. Imported naturalized plants, in particular weeds, are considered a natural link in the chain of a flora.
The makeup of a particular flora is to some extent arbitrary, since it depends on the size of the region under study. The object of study and description may be the flora of a country, for example, the flora of the USSR. Sometimes the flora of only certain parts of a country is studied, for example, the flora of Leningrad Oblast. Also studied are the floras of territories independent in respect to their natural history (for example, the Caucasus or Middle Russia), botanicogeographic regions, (for example, Manchuria or Antarctica), or parts of the earth that are more or less isolated by natural boundaries (for example, Iceland and Kamchatka).
Analysis of a particular flora is based on the species and genus composition. The various species are subdivided according to specific characteristics into elements of the flora. Specifically, geographic elements unite species with the same geographic distribution, and genetic elements unite species that are closely related in geographic origin and history of distribution. In the course of botanicogeographic (geographic and genetic) analysis, the relationship of the flora under study with other floras is determined. Ecophytocenological analysis delimits elements of flora according to their connection with ecological conditions and with various types of vegetation. Age analysis makes it possible to identify progressive (young in time of origin and in time of distribution), conservative, and relict elements. Relicts are regarded as survivals of past states of the vegetational cover. The availability of paleobotanical data makes it possible to determine the age of certain elements of a flora and the time the elements became part of the flora.
One of the most important features of a flora is the systematic structure, that is, the existence of representatives of various systematic groups that are characteristic of various botanicogeographic regions. There are definite quantitative ratios between each group. Changes in these ratios are among the most important factors in the comparative characterization of floras.
In the first approximation the richness of a flora is determined according to an inventory of the various species and genera. However, the dependence of the number of species and genera on the size of the habitat of each flora hampers a comparative evaluation of the richness of floras. Methods for comparative study of floras are needed that ensure the comparability of juxtaposed data—approximate equality of the quantitative indexes that characterize various floras. The method of studying specific floras yields the best possibilities for comparative determination of the richness of floras. Analysis of the inventory of species and genera, particularly geographic and genetic analysis, and a comprehensive comparative interpretation serve as the basis for floristic regionalization of the earth.
The term “flora” is the traditional heading for comprehensive treatises on the systematic composition of the plant world in a given region. Floras contain detailed descriptions of plant species, keys for identification, data on growth conditions and geographic distribution (on the territory encompassed by the flora and throughout the world), and information about economically important properties and uses of the plants. The territory covered by an individual flora is determined by the extent of field work conducted in preparation for publication. Many floras summarize the knowledge of the systematic composition of the plant world of a given territory, thereby serving as an important basis for further botanical study.
A. I. TOLMACHEV
in Roman mythology, the goddess of flowers, youth, and spring flowering. The Floralia, a festival celebrated in honor of Flora, consisted of games that sometimes took on a licentious character. In art Flora has frequently been depicted as a young girl with flowers; the goddess has been the subject of works by many great artists, including Titian, Poussin, and Rembrandt.