HYPNACEAE 8 I 



This family is a large and somewhat heterogeneous one and 

 includes practically all the pleurocarpous mosses with elongated 

 smooth leaf cells and well developed peristomes, i. e., having 

 broad keeled segments and, usually, well developed cilia. Al- 

 though the leaf cells are often short and broad, they are more or 

 less rhomboidal or elongated-hexagonal in outline and in the 

 middle of the leaf are never regularly oval, rounded, or quad- 

 rate. 



The mosses of this family may be found in all kinds of habitats, 

 and some individual species have a wide range of habitat. 



The classification of this family is a matter upon which no 

 two bryologists would be likely to agree. No single character 

 can be relied upon as a basis of classification, and it is extremely 

 difficult to select combinations of characters that will indicate 

 relationships with any degree of accuracy. Many characters 

 relied upon in the past are almost certainly very highly modified, 

 if not actually produced, by habitat conditions. Short thick- 

 walled leaf cells are so frequently correlated with a xerophytic 

 habitat as to suggest a causal relation. There is almost cer- 

 tainly a relation between habitat and the curvature and direc- 

 tion assumed by the capsule, and between this last and the com- 

 pleteness of the peristome. These statements, of course, apply 

 to mosses outside this family, but the difficulties in classifica- 

 tion caused by these facts are particularly prominent here. 



The following grouping into subfamilies is primarily based 

 more on the structure and robustness of the costa and the 

 presence or absence of central strand in the stems than in most of 

 the older groupings. For exceptions to the characters indicated 

 in this key see the descriptions of the subfamilies. 



Key to the Subfamilies of the Hypnaceae 



I — Costa strong and extending to the middle of the leaf or beycnd, 



nearly always single, (exceptions in Hylocomium and Campylium) . . 3 



Costa short and double or lacking 2 



2 — Capsules erect and symmetric, or nearly so; cilia of inner peristome 



rudimentary or lacking Entodonteae 



Capsules unsymmetric, more or less curved, usually cernuous. .Hypneae 

 3 — Plants large, secondary stems stout and dendroid from creeping or 



stoloniferous primary stems 4 



Plants smaller, scarcely dendroid 5 



