512 A. HESSELBO 



Grows on stones and dry or soniewhat damp rocks, and appears 

 to be frequent, although not abundant, in all parts of the country up 

 to about 300 melres above sea-level. In NW. Iceland it is very common 

 on stony slopes, and is often richly fruiting while it has or less been 

 found sterile only. 



227. Lescuræa Breidleri (Kindb.) Arn. et Jensen. 



Plijchodiiim oligocladnm Limpr. 



E. Iceland: Berutjardarskard!, at an altitude of 600 metres; Seydis- 

 tjordur!, 500 metres. N. Iceland: Reykjahlid!; Akureyri, at an altitude 

 of about 770 metres!. Grimsey (O. D.)!; Oxnadalsheidi (Grl.) ! . NW. Ice- 

 land: D.\rafjordur!; Gnupsdalur!; Isafjordur!; Sugandaljordur !; Grunna- 

 vik!. S. Iceland: Barkarstadr!, at an altitude of 530 metres. 



Frequent on rocks and stones in the more highly situated parts of 

 the country. It occurs in greatest abundance and in its most typical 

 form on mountain heights at elevations of above 500—600 metres, where 

 it is often the most abundant constituent of the vegetation. It has its 

 main distribution in NW. Iceland, where, for instance around Isatjordur 

 and Sugandafjordur, it occurs very abundantly on the rocky flåts from 

 about 200 metres upwards. $ piants are common, (^ piants and fruit 

 have not been observed. 



Lescuræa filamentosa and L. Breidleri, judging from the Iceland spe- 

 cimens, are well-deiined forms which, as a rule, may easily be distin- 

 guished from each other. 



L. filamentosa is the lowland form, which has its main distribution 

 in the birch region, and does not ascend much higher than about 300 

 metres above sea-level. Here it forms low, dense, dark-green or blackish- 

 green tufts on stones, and prefers somewhat damp localities. (^ piants 

 are very frequent. ^ piants occur more rarely. 



L. Breidleri is the Alpine form, which descends only by exception 

 to the upper limit of the birch region. It forms deep, loose, yellowish 

 tufts of great extension upon the dry stony slopes of the mountain 

 heights, or upon large blocks of rock. Only sterile ^ piants have been 

 found. Both the habit and the colour easily distinguish the two species 

 from each other. L. Breidleri is almost branchless, but with some long, 

 ascending branches often hook-shaped at the apex; L. filamentosa is 

 densely and irregularly branched. In its most lowly situated habitats, 

 for instance near Reykjahlid at an altitude of about 300 metres, and 

 in some localities in NW. Iceland, L. Breidleri shows, however, a tendency 

 to develop forms which approach in habit the vigorous forms of L. 

 filamentosa var. hrachyclados. The leaf-cells in all the investigated spe- 

 cimens of L. filamentosa were short, oval or roundish and thick-walled, 

 more or less but always distinctly papillose, frequentlj' as far down as 

 to the leaf-base, the nerve was very rough at the back, which features 

 most certainly distinguish doubtful forms frorti L. Breidleri. In the latter 

 species the leaf-apex is longer, the nerve is narrower towards the apex 

 and usually smooth, rarely indistinctly toothed at the back. The leaf- 

 tissue in L. Breidleri is much more translucent than in L. filamentosa. 



