THE EVOLUTION OF HERBACEOUS PLANTS 



295 



aggressive herbaceous flora. Most of the dominant and widely 

 spreading plants of today, including practically all weeds, originally 

 belonged to this northern herbaceous vegetation. These "Scandi- 

 navian" plants have taken advantage of every opportunity to 

 become widely dispersed and to establish themselves in other parts 

 of the world, with the result that in the temperate regions of the 

 Southern Hemisphere, for example, there are well over two hundred 

 genera and even fifty or more species which are identical with 

 northern ones; and in practically all the south temperate floras 

 more than half of the herbaceous genera either have their center of 

 distribution in the Northern Hemisphere or are very common there. 

 There are comparatively few southern genera, on the contrary, 

 which have successfully invaded the North. 



That the evolution of herbs has taken place for the most part 

 since the close of the Mesozoic is indicated not alone by the fact 

 that refrigeration of climate seems to date from that time but also 

 from the following phytogeographical evidence. In the four great 

 temperate land masses of the Southern Hemisphere (AustraKa, New 

 Zealand, temperate South America, and South Africa) the endemic 

 genera and the very characteristic families, which undoubtedly 

 represent the most ancient element in the vegetation, are com- 



TABLE II 



Total 



Herbs 



Percentage 

 Herbs 



Australia — 

 Species of 

 Species of 



New Zealand — 

 Species of 

 Species of 



Patagonia — 

 Species of 

 Species of 



South Africa — 

 Species of 

 Species of 



non-endemic genera 

 endemic genera .... 



non-endemic genera 

 endemic genera. . . . 



non-endemic genera 

 endemic genera .... 



non-endemic genera 

 endemic genera .... 



2,301 

 4,024 



711 

 315 



920 

 667 



3,298 

 4,686 



1,251 

 677 



460 

 109 



720 

 320 



1,929 

 1,390 



54 

 17 



34 

 76 



55 

 29 



posed, in very large majority, of woody plants,^ as shown in Table H. 

 Most of the indigenous herbs, however, belong to genera, and often 



' "Endemic" genera are those which are either strictly confined to the region in 

 question or have only a very few species outside of it. 



