fulltext - DiVA

208 ERIK JULINserina ssp. Egedii, Chamaedaphne calyculata, Primulasibirica ssp. finmarchica, Lactuca sibirica andChaerophyllum bulbosum ssp. Prescottii; the lastspecies does not occur in this area however, butconsiderably farther north, near Pajala.Many species occur in a much greater frequencyon the Finnish side of the Torne river than on itsSwedish side. This is true above all of a great numberof species that here in the north are more orless exclusive to rich fen, e.g. Calamagrostis canescens,Eriophorum latifolium, Rhynchospora alba,Carex diandra, C. panicea, C. flava, C. capillaris,Orchis incarnata, Gymnadenia conopsea, Listera ovata,Salix myrsinites, Stellaria crassifolia, Saxifragahirculus, Saussurea alpina, Cirsium palustre andCrepis paludosa. The same conditions are validfor a few species preferring dry soil, e.g. Dianthussuperbus, Pimpinella saxifraga, Fragaria vesca andGalium verum and some apomictic microspeciesbelonging to the genera Taraxacum, Hieracium andRanun:culus (auricomus group). In contrast only afew species seem to be more frequent on the Swedishthan on the Finnish side of the river: Isoetesechinospora, I. lacustris, Sparganium angustifolium,Carex macloviana, C. lapponica and Sedum annuum.The surroundings of the Torne River thus constitutea transitional floristic area. This is due inpart to the westward progress of the eastern elements,in part to the generally richer flora in theedaphically favourable area that is chiefly situatedon the Finnish side of the frontier.THE PRIMULA SIBIRICA GROUP.-Some seashoreplants have a disjunct area on the Gulf of Bothnia(occasionally even reaching the Baltic proper),separated from their main distribution area on theshores of the Arctic Ocean. This group, known as thePrimula sibirica group, includes Primula sibirica(nutans) ssp. finmarchica (see further L. & Y. M.A.KI­NEN 1964), Carex halophila, C. paleacea, C. glareosa,C. Mackenziei, Potentilla anserina ssp. Egediiand Sonchus arvensis var. bottnicus (see below).Puccinellia phryganodes and H ippuris tetraphylla(absent in the north-east corner of Sweden) alsobelong to the group which is considered to haveimmigrated from the White Sea to the Gulf ofBothnia in early Post-glacial time when the dis-tance between these waters was quite short. As aslight salinity might have been favourable the periodin question might have been that of the YoldiaSea about 9000 years ago. A similar disjunct distributionhas for instance Potamogeton vaginatus, aspecies of brackish water, and Arctophila fulva var.pendulina, growing near fresh water, with its mainFennoscandian occurrence along the Torne river.TRENDS TOWARDS ENDEMISM.-The long andnarrow coastal zones and the archipelagos of theBaltic seas occasionally during the sequence oftheir history may have favoured the isolation ofplant populations in limited areas. Differences inclimate and salinity between the north and thesouth, and in particular changes during the differentepochs of the Baltic development, might haveexerted an influence cauing tendencies towardsendemism in some of these populations. Eventhough the time has been short, hardly more than10,000 years, the difficulties of immigration andinitial dispersal might have contributed to theseparation. Among sexual endemics only very fewhave reached a state of separation on the specificlevel. Three of these, Deschampsia bottnica, Euphrasiabottnica and Artemisia bottnica (A . borealis ssp.bottnica) occur in the north-east of Sweden. Oncloser examination possibly more of the seashoreplants within the area might prove to differ fromthe main types, although still constituting populationsof low taxonomic value. Examples are Artemisiavulgaris var. coarctata, Silene nutans with anisolated population growing on sand dunes on acouple of islands in the archipelago off Haparandaand probably belonging to its var. infracta, andseashore ecotypes of Euphrasia frigida, having anarea probably disjunct from that of the mountainecotype. Only weakly differentiated are the seashoreecotypes of V icia cracca and Chrysanthemumvulgare, which through their habit are distinguishablefrom the ecotypes of the same species growingas weeds. Sonchus arvensis var. bottnicus accordingto MARKL UND ( 1940) has a population along theBothnian Bay having completely glabrous involucresand stalks, and another population on theshores of the Gulf of Finland, slightly glandulous onthe same parts..Acta Phytogeog1·. Sue c. 50