HYPNACEAE 101 



2 — Leaf cells short, 2-5: 1 Amblystegiella 



Leaf cells usually narrowly linear-flexuose 3 



3 — Costa usually pronounced; aquatic! Hygrohypnum 



Costa faint or lacking 4 



4 — Epidermal cells of capsule strongly collenchymatous; operculum 



beaked Raphidostegium 



Epidermal cells of capsule not collenchymatous 5 



5 — Alar cells little differentiated Plagiothecium species 



Alar cells strongly differentiated, inflated 6 



6 — Leaves spreading to squarrose as in Campylium; capsules striate. 



Plagiothecium striatellum 

 Leaves imbricated; capsules not striate, long-cylindric. 



Hypnum Haldanianum 



HYGROHYPNUM Lindb. 



Aquatic or subaquatic mosses growing on stones in and near the 

 beds of brooks, especially in mountainous regions, often forming 

 extensive mats, more or less filled in below with sand and gravel. 

 Stems mostly creeping or prostrate, with ascending branches; 

 central strand present, usually few-celled. Leaves in most 

 species usually concave, more or less falcate-secund, compar- 

 atively short and broad, soft in texture and often obtuse at apex, 

 rarely acutely acuminate, sometimes apiculate, mostly entire or 

 slightly denticulate at apex; costa double, of varying length, or 

 single and forking, sometimes reaching above the middle; alar 

 cells plainly differentiated, hyaline, colored, or subopaque in the 

 various species, often remaining on the stem when leaves are 

 stripped off for examination. Capsules inclined and unsym- 

 metric, rather short and thick; peristome perfect. 



Nearest to Drepanocladus, from which it is distinguished by- 

 its habitat in running streams and its broader concave more 

 obtuse leaves. Scorpidium is distinguished from this genus by 

 its gigantic size and rugose leaves; Collier gon by its habitat and 

 general appearance. Aquatic Raphidostegia are very close to 

 some species of Hygrohypnum, and Limpricht and Brotherus put 

 Hypnum Novae-Caesareae Austin in this genus, but in general 

 the alar cells of Raphidostegium are more strongly developed, 

 the costa is shorter or wanting, and the operculum rostrate. 

 Certain Brachythecieae, such as B. plumosum or Eurhynchium 

 rusciforme have a similar habitat and appearance, but are easily 



