032 A. HESSELBO 



291. Hypnum Kneiffii (Br. eur.) Schimp. 

 Amblystcginw Kneiffii Br. eur. 



This species is common, especially in N. and E. Iceland, and is 

 somewhat rarer in NW. and S. Iceland. It grows in ver}' wet situations 

 in bogs, in pools, along the banks ol' rivers or covering stones in the 

 water. 



Aquatic forms with slightly secund, longly pointed leaves are fre- 

 (juent; short and broad leaved orlhophyllous or drepanophyllous forms 

 occur more rarely. The size of the leaf-cells is dependent on the form 

 of the leaf; in f. brevifolia they are short in the middle of the leaf, 

 about 3—4 times as long as they are broad. In Esja a brevi-orthophyllous 

 form was collected in a moss-bog at an altitude of 410 metres. 



It has been collected in fruit only ncar Husavik in N. Iceland. 



292. Hypnum exannulatum (Giimb.) Br. eur. 



Amblystegiiiin exanniilatiiin De Not. 



Very common. 



Hypnum exannulatum occurs in numerous forms everywherc on a 

 damp substratum, often forming the bulk of the vegetation, either alone 

 or mixed with other Hypnaceæ {H. slramineum, H. revolvens, etc), with 

 Cinclidium, Mnium spp., and other bog mosses. It grows not only in 

 bogs. but also in pools, moss-bogs, along streams. and occasionally on 

 damp rocks. Near Akureyri it was abundant even at an altitude of 

 600 metres. 



Var. ptnjttirascens (Schimp.) (Hypnum purpurascens Limpr.) is the 

 most frequent form, at any rate in N. and E. Iceland. It is usually 

 purplish, more rareh' green, ercct, as much as about 20 cm. high, and 

 often forms large, pure growths on very wet ground, especially in the 

 water itself, for inslancc along the banks of small streams. In this form 

 the leaf- base is never decurrent. In the piants which have becn in- 

 vestigated the cells of the leaf base are sometimes quite typical, forming 

 a single row of large dilated cells across the entire leaf-base, and some- 

 times they approach those of the type by forming a more or le^s large, 

 triangular group of empty cells towards the leaf- margin. In typical 

 Hypnum exannulatum the leaves are ahvays narrowly decurrent. 



Var. Rofæ (De Not.) is without doubt an extreme aquatic form of 

 var. purpurascens, with which it is closely connected by intermediate 

 forms. It has the solid, tough stem with long, forwardly dirccted 

 branches and very narrow, slightly secund leaves peculiar lo all mosses 

 growing in swiftly flowing water. The nerve is very strong, usually 

 0.10 mm. wide at the base and, as a rule, vanishing in the apex, more 

 rarely excurrent. It grows in running water. often in streams flowing 

 through boggy ground. Typical specimens were collected in the following 

 localities: E. Iceland: Seydisfjordur !. rather common; Breiddalskard!; 

 Frodarheidi iH. J.;!. NW. Iceland: Kaldalon!; D.\njandil. W. Iceland: 

 Hvammur GrI.)!; Esja!, at an altitude of 100 metres. Only sterile 

 specimens have been found. 



