174 EILIF DAHL 



Europe and America. This brings up the question of how to discriminate 

 between native and introduced plants. 



This is not a serious question as far as recent dispersal is concerned where 

 often, if not the actual introduction, the subsequent phase of dispersal in the 

 new country has been observed. It is much more difficult if the introduction 

 took place long before any systematic botanical investigations were carried 

 out. 



In general more species seem to have been spread from the east towards the 

 west than vice versa and the problem is not very difficult as far as American 

 species introduced to Europe is concerned. 



The question of the impact on the flora of the Norse colonists in Green- 

 land and Iceland has been discussed by many authors. Ostenfeld (1926) 

 believed that as much as 14 per cent of the Greenland flora had been introduced 

 this way whereas Porsild (1932) thinks this figure too high, probably not more 

 than 5 per cent. Modern intensive studies in the infra-specific races throw 

 hght on these questions since among the anthropochorous species (species 

 following human occupation) some races may be anthropochorous and others 

 not. Also palynological research is of help ; e.g. Angelica archangelica which 

 has been suspected of being introduced to Greenland by Norse colonists 

 has been identified in pollen deposits considerably older than the Norse 

 colonization (Iversen, 1953). But still, several doubtful cases are known. 

 I have here accepted the evaluation given by Bocher, Holmen and Jakobsen 

 (1957) regarding Greenland, and Love and Love (1956) regarding Iceland. 



In Newfoundland and adjacent areas a peculiar isolated European element 

 of plants occurs which Fernald (1929) considered a relict, indigenous element. 

 However, Lindroth (1957) has pointed out that many of the species were 

 probably introduced during the period of fishing as early as in the sixteenth 

 century by British, French, and Iberian fishing boats carrying ballast west- 

 wards and throwing it ashore and bringing fish back. For this reason, all 

 plants apparently native only in the Newfoundland-Nova Scotia area in 

 America, but common somewhere along the coast from south England to 

 Portugal and taxonomically indistinguishable from the European populations, 

 have been considered here as introduced by man during the early fishing 

 period. This makes a list of about 60 taxa (species and taxonomic entities of a 

 lower rank than species) to be excluded from the number of possible Amphi- 

 Atlantic plants. 



THE WESTERN AMPHI-ATLANTIC ELEMENT IN EUROPE 



AND THE EASTERN AMPHI-ATLANTIC ELEMENT IN 



AMERICA 



A western Amphi-Atlantic element in the flora of Europe can be recognized, 

 consisting of taxa found in eastern America and not occurring east of the 

 River Lena, the Carpathians and the Balkans in the Old World. Altogether 83 



