Chapter XI 

 CONCEPT OF FLORAL ELEMENTS 



An investigation of the origin and history of development of a flora 

 should be based on a study of paleobotanical data and an analysis of 

 the areas of the species of which the given flora is composed. As a 

 result of such an analysis, the flora may be subdivided into definite 

 groups of species. In making this subdivision it is necessary, first of all, 

 to ehminate not only the "aliens" and "escapes" but also the "wides", 

 i.e., species having such an extensive range that they embrace in their 

 area of distribution several phytogeographical regions. Such widely 

 distributed species, called by EiG (1931) "polychores" or "pluri-re- 

 gional species", cannot give any clues to the origin and history of a 

 flora, at least not unless their centers of origin and time of dispersal 

 have been determined. After these three types of species have been 

 eliminated, the remaining species may be classified into a number of 

 groups, which are termed floral elements. 



The endemic species in the flora under investigation should first be 

 studied. It would be erroneous to consider that endemic species, since 

 their areas are limited to the given flora, do not require analysis. The 

 establishment of relationships between endemic species, of neo- and 

 paleoendemism, and, in the latter case, the determination of the former 

 areas of these species, as well as the determination of geographical 

 series of vicarious species — all this gives very important clues to the 

 origin of a flora. The remaining species should then be divided into 

 groups according to the geographical character of their areas. This will 

 make clear the regions from which these groups of species originated, 

 and from these data the genesis of the given flora may be established. 

 In other words, on the basis of a geographical analysis of its component 

 species we may establish the origin of any given flora. 



The concept of floral elements, as we have defined it, appears so 

 simple that any special explanation would seem superfluous. In fact, 

 however, due to the conflicting interpretations that have been given to 

 this concept, the question assumes considerable complexity. It seems 

 advisable, therefore, to summarize briefly the various points of view. 



The concept "phytogeographical element" was first introduced into 

 science simultaneously by two investigators: by Christ (1867) in his 

 investigation of the origin and distribution of the flora of the Alps and 

 by Areschoug (1867) in his history of the Scandinavian flora {see also 

 Degelius, 193s). But even earlier a number of writers, e.g., Willde- 

 Now (1802), Unger (1852), Hooker (1855), and others, in giving 

 analyses of floras, had in mind precisely such groupings of species, al- 

 though they did not use the term "element". 



The grouping of species within any given flora may differ widely 

 according to the principle upon which this grouping is based. A sur- 

 vey of this problem was first made by Jerosch (1903) in her book 

 devoted to a history of the flora of the Alps. Many investigations of 

 the same problem have since been made — by Schroter (1913), 



