VASCULAR PLANTS COMMON TO THE ARCTIC AND THE BRITISH ISLES 99 



Carex panicea - 112, H40. 

 C. vaginata - 16. 



C. magellanica s.l. (incl. C. paupercula Michx.) - 18, Hi. 

 C. rari flora - 6. 



Calamagrostis neglecta s.l. - 6, H4. 

 Nardus striata - 111, H39. 

 TOTAL = 48. 



Extinct are : 



Pinguicula alpina - formerly 1. 



Senecio congestus - formerly 8, according to Druce (1932). 



There are thus 309 species of vascular plants which are common to the Arctic and 

 the British Isles - at all events according to my computation and rather broad view of 

 specific limits. Of these a total of 172, or 55-66%, are to at least a considerable extent 

 * open soil ' plants or ones commonly to be found in habitats where there is little or no 

 competition, while a further 89, making a total of 84-98%, are fairly frequently to be 

 found growing in such circumstances. These percentages are lower than in the former 

 analysis, particularly owing to the extension southward of the coverage into regions 

 where open habitats no longer preponderate, although the higher one is only slightly 

 lower than its earlier counterpart. Altogether this affords solid confirmation of the earlier 

 contention that the majority of British vascular plants which reach the Arctic grow largely 

 in the absence of competition, while many more, comprising in all the vast majority, 

 are fairly frequently to be found in open habitats. Moreover, many of the above-mentioned 

 48 species that are normally restricted to closed habitats are occasionally to be seen growing 

 in open ones, though not to an extent which would seem to warrant any suggestion that 

 this circumstance might be phytogeographically significant. 



The further circumstance that many of the predominantly boreal plants which extend 

 far south do so largely on calcareous substrata has been noted e.g. by Patton (1923); 

 at least in some cases it seems likely that this may be due to the tendency for more open 

 vegetation and less competition in such areas, especially where precipitation and tem- 

 peratures are relatively low, although this would seem a worthy subject for future investiga- 

 tion. 



In all, 874 species of vascular plants are so far known to inhabit the Arctic, of which 

 833 are native and 41 apparently alien. Of these last, as indicated in the above lists, 

 at least 33 are natives of the British Isles, 6 more being considered aliens there also, 

 while at least 3 native arctic species appear to have been introduced into Britain. It 

 seems that only a single plant which has been introduced in the Arctic, Agrostis scabra, is 

 unknown in Britain in anything approaching a wild state, though presumably others will 

 be added when the arctic parts of the U.S.S.R. become better known to western civilisation. 

 The above figures also indicate that in the present-day native British flora there are 

 represented no less than 267 of the 833 recognized species of native arctic vascular 

 plants ; this is a percentage of just over 32. If aliens are included in the calculations, the 

 percentage rises considerably. 



REFERENCES 



CLAPHAM, A. R., TUTIN, T. G., & WARBURG E. F., 1952, Flora of the British Isles; Cambridge. 

 DRUCE, G. C, 1932, The Comital Flora of the British Isles ; Arbroath. 



LOUSLEY, J. E., 1951, Recent research and additions to the British flora, Nature, 168, 934-936. 

 , 1952, The changing flora of Britain, Nature, 169, 1076-1079. 



PATTON, D., 1923, Variations in the vegetation along the outcrop of the Lawers-Caenlochan schist, Rep. 

 Bot, Sac. and Exch. Club British Isles, 1922, 6, 797-807. 



