THE GENUS EQUISETUM 



number, are virtually devoid of direct fossil history. Nevertheless, signs of age are not 

 lacking from the evidence of geographical distribution. The total distribution of the 

 living genus is almost worldwide, though Australia and New Zealand contain none and 

 there are relatively few species in the southern hemisphere and in the tropics. With this 

 proviso it is striking that at least half of the living species have a distribution which 

 straddles the entire range of the genus, and all the European species are at least circum- 

 polar. Only in America can there be found any considerable number of species which 

 do not extend beyond that continent. These facts are perhaps most clearly revealed by a 

 citation of the general distribution of the European species, and since only two of these 

 are non-British and all are quoted in Hegi's Flora, the information easily obtainable from 

 this source is reproduced in the following list : 



Species General distribution 



E. sylvaticum L. North and central Europe, north Spain, Balkans, north Asia, North America. 



E. pratense Ehrh. British Isles, north- and east-central Europe, Caucasus, Siberia, North America. 



E. maximum Lam. Europe (except Scandinavia and a large part of Russia), west Asia, western North Africa, 



North Atlantic Islands, western North America. 



E. arvense L. Europe, north Asia, North Africa, Canaries, South Africa, North America. 



E. palustre L. Europe (except for parts of the Mediterranean region), Caucasus, temperate Asia, northern 



North America. 



E. limosum Willd. Europe (except for parts of the Mediterranean region), north Asia, North America. 



E. ramosissimum Desf. South and central Europe, temperate Asia, India, China, most of Africa (including Mada- 

 gascar), America both north and south. 



E. hiemale L. Europe (except parts of Mediterranean region), north Asia as far as Japan, North America. 



E. variegatum Schl. Europe (except for the true Mediterranean region and certain parts of the Danube countries, 



Russia and Denmark), Siberia, North America. 



E. scirpoides Michx. North Europe (Iceland, Spitzbergen, Scandinavia), Siberia and northern and arctic 



America. 



Outstanding in this list are E. arvense and E. ramosissimum, which are not only circum- 

 polar but present in the southern hemisphere also. Other interesting distributions are 

 those of £■. maximum and E. scirpoides. The former, though circumpolar in total extent, is 

 discontinuously so to an extreme degree, being present on the west sides of Eurasia, 

 Africa and America, but not on the east of these continents. This strongly suggests 

 regional extinction on a large scale, an event which can scarcely be entirely recent. 

 Direct signs of local extinction are given under somewhat different circumstances by 

 E. scirpoides (Fig. 211). This is not a British plant, having on the whole a more northerly 

 distribution, being met with right into the Arctic circle in Europe, Siberia and America. 

 It has, or perhaps had, in addition, one outlying station in central Europe, namely, at 

 Heihgenblut near the Pasterze Glacier in Austria. It was well known in this locality a 

 hundred years ago, though it has not been seen recently and may have died out. Since 

 this species is inconspicuous and of no economic or horticultural importance, it is im- 

 possible to imagine that either its introduction or its extermination, if it is in fact exter- 

 minated, in a station many hundreds of miles away from its main areas of occupation 

 can owe anything to human interference, and it therefore seems necessary to suppose 

 that both events are indicative of important changes of climate. E. scirpoides in central 

 Europe seems, in fact, to be a relict from glacial times, and if this is correct, one must 



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