532 A. HESSELBO 



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

 Amblgstegium 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 very wet situations 

 in bogs, in pools, along the banks of rivers or covering stones in the 

 water. 



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

 quent; short and broad leaved orthophyllous 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 near Husavik in N. Iceland. 



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



Amblystegium exannulatum De Not. 



Very common. 



Hypnum exannulatum occurs in numerous forms everywhere on a 

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

 or mixed with other Hypnacecc (H. stramineum, 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. purpuntxcens (Schimp.) (Hypnum purpurascens Limpr.) is the 

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

 purplish, more rarely green, erect, as much as about 20 cm. high, and 

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

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

 the leaf -base is never decurrent. In the plants which have been 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 alwaj's narro\vly decurrent. 



Var. Rotcv (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 directed 

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

 growing in swiftty 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 (lowing 

 through boggy ground. Typical specimens were collected in the following 

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

 Frodarheidi (H J.)!. NW. Iceland: Kaldalon!; DVnjandi!. W. Iceland: 

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

 specimens have been found. 



