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Vegetation of coastal Bohusliin 115Fig. 2. A characteristic featureof the vegetation of the coastalrocky hills is the Calluna heathoccupying crevices with a littlesoil, whereas only lichens andmosses adhere to the once icescouredand sea-worn granite rockitself. Otteron Island, Tanum,northern Bohuslan. Aug. 8, 1964.Photo H. P. Hallberg.1937, 1955). On many shores, Elymus is the onlyspecies, but in North Bohusliin the number ofspecies is generally greater. Sometimes Ammophilaarenaria, Asparagus officinalis, Agropyron junceiforme,Eryngium maritimum, and Lathyrus maritimus,which are all rare in BohusHin, can be seenon one and the same shore.Non-littoral rock vegetation and Calluna heathROCK AND CREVICE VEGETATION.-0n the rocksfurther inland, which are not so strongly affectedby the proximity to the sea, a number of lichen andmoss communities grow that differ from those ofthe shore (DEGELIUS 1939, cf. Du RrETZ 1925 a).On the north-facing slopes, Lecidea taeniarum andL. tenebrica are common among the crustaceouslichens, and species of Cladonia, Parmelia andU mbilicaria among the fruticulose and foliaceouslichens. The crustaceous lichen communities exposedto wind and sun are often dominated byLecanora spp. (Aspicilia) or by Rhizocarpon geographicum,etc., and the foliaceous lichen communitiesby Parmelia spp. On surfaces with trickling· water the Umbilicariaceae are the most frequent.The shallow soil of the small rock crevices andclefts harbours many different communities. In thebare skerry region, on soil deficient in nutrients, therare Atlantic Sedum anglicum - Sagina subulataassociation (TuxEN 1951, p. 160, GILLNER 1964a,p. 223) is to be found. :Irairly rare is also the SubatlanticAira praecox - Sedum rupestre association(TUXEN 1951, p. 163, HALLBERG 1959, p. 56). AW oodsia ilvensis - Asplenium septentrionale communityis present in small fissures that are deficientin soil (BLoM 1929, p. 294, TuxEN 1951; p. 167).Far more frequent is another rock crevice communitythat appears throughout BohusHin. In thecoastland, it is represented by .l;lgrostis canina ssp.montana, Aira praecox, Rur(l;ex acetosella (mainly ssp.tenuifolius), Scleranthus perennis, Silene rupestris,Viscaria vulgaris, Viola tricolor, Polytrichum juniperinum,P. piliferum, several Cladonia species, etc.(SKOTTSBERG 1925, p. 44; it resembles Agrostideto­Rumicetum tenuifolii in the study by TuxEN 1951,p; 160). Further, species such as Sedum acre,Saxifraga granulata, Potentilla argentea, Lotus corniculatus,and others, occur in greater quantities thanotherwise in the rock crevice vegetation in contactwith arable land or pastures.HEATHS.-The Calluna heath of coastland BohusHin(ATLESTAM 1942) usually differs from thetype that occurred earlier in large areas of Hallandand Vastergotland. Calluna vulgaris grows in Bohuslanin the rock fissures, seldom on soils of anymarked thickness. On the boulder-fields that occasionallycover the rock, it is replaced by communitiesdominated by Vaccinium myrtillus. In theActa Phytogeog.r. Suec. 50