ENDEMISM AS A CRITERION OF ANTIQUITY 

 AMONG PLANTS 



Edmund W. Sinnott 



Connecticut Agricultural College 



Those species, genera, or families of plants which are restricted 

 in their distribution to a particular region, and which from this 

 circumstance are termed "endemic" in that region, have frequently 

 been regarded as constituting the most ancient element in its 

 flora. A discussion of the extent to which this characteristic of 

 endemism may be used as a safe criterion of antiquity, particularly 

 when we are dealing with plants belonging to different growth 

 forms, is the purpose of the present paper. 



An ecological analysis of the endemic elements in the floras of 

 various regions throughout the world provides us with some sug- 

 gestive facts which bear on this problem, for such an analysis 

 shows that the important endemic types in the north temperate 

 zone are radically different from those in the south temperate zone. 

 The writer has compiled a list of the genera of dicotyledons which 

 have 95 per cent or more of their species confined to Canada, the 

 United States, and northern Mexico, and which may therefore 

 fairly be said to be "endemic" in temperate North America. 

 These genera comprise over 2,200 species, of which only 235, or 

 slightly over 10 per cent, are trees or shrubs. In the non-endemic 

 portion of the flora of this region, on the contrary, approximately 

 25 per cent of the species are woody plants, over twice as large a 

 proportion as in the endemic. An analysis of the essentially 

 endemic genera of Europe and adjacent temperate Asia and 

 Africa reveals a similar preponderance of herbs here as compared 

 with the non-endemic types. 



In the southern hemisphere, however, precisely the reverse is 



true. In Australia, for example, 83 per cent (3,347 out of 4,024) 



of the species of the endemic genera are trees or shrubs, but only 



37 per cent (623 out of 1,687) of the species of the non-endemic 



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