236 American Midland Naturalist Monograph No. 6 



long to very long; capsule inclined to horizontal, cylindric, arcuate, when dry 

 constricted below the mouth, smooth, annulate; lid convex, apiculate. 



A difficult genus of over 40 species of water-mosses, quite largely swamp- 

 mosses, — often formmg quite large masses of vegetation, — almost exclusively 

 confined to temperate and cold regions; about 22 species occur in North Amer- 

 ica, perhaps the following 8 to be included in our list. Species not well- 

 defined and extremely variable. See Grout's Moss Flora for descriptions of 

 many forms and varieties. 



Key to the Species 



A. Stem without central strand or inflated cuticular cells; leaves without inflated alar 



cells 2. D. vernicosus 



A. Stems with central strand B 



B. Stem in cross-section displaying cortical layer of enlarged, thin-walled, hyaline 



cells E 



B. Stem without enlarged cuticular cells C 



C. Leaves usually entire ;— F 



C. Leaves serrulate, ends of stems and branches hooked D 



D. Costa usually less than three-fourths length of leaf; alar group of cells not reach- 

 ing over to the costa 7. D. ftuitans 



D. Costa extending well up to the apex of leaf; alar group of cells large, excavate, 



and extending over to the costa 8. D. exannulatus 



E. I eaves strongly plicate, 3-5 mm long I. D. uncinatus 



E. Leaves not plicate, about 2 mm long 3. D. intermedius 



F. Ends of stems and branches more or less strongly hooked (See also forms of 



D. Kneiffti) G 



F. Ends of stems and branches not or but moderately hooked (certain forms strongly 



hooked); leaves broad-lanceolate to ovate-oblong 5. D. Kneiffti 



G. Stem-leaves falcate-secund; enlarged, inflated, thin-walled, auricular cells usually 



reaching nearly to the costa; costa usually about to middle of leaf 4. D. adur.cus 



G. Enlarged, medium thick-walled, auricular cells not reaching costa; costa usually 



extending into the acumen 6. D. Sendlneri 



1. Drepanocladus uncinatus [Hedwig] Warnstorf 



{Hypnum uncinatum Hedwig; Amblystegium aduncum Lindberg) 



Rather slender and loosely interlaced, pale green or golden green: stems 

 distantly and irregularly pinnately branched, 2-10 cm long, in cross-section 

 showing a layer of large hyaline cortical cells and a central strand; leaves 3-5 

 mm long, rather crowded, regularly falcate to sub-circinate, little altered when 

 dry, spirally fllcxuous at the points in the younger and softer branches, narrov/- 

 ly elongate-lanceolate, strongly plicate both wet and dry, gradually very long 

 and slenderly acuminate, usually denticulate above, texture very thin; costa 

 narrow, about 0.30-0.35 mm at base, extending well into the acumen; leaf-cells 

 very long, linear- flexuous, thin-walled, pointed, uniform to the base and apex, 

 the alar forming a rather small and indistinct group of slightly enlarged and 

 slightly mflated cells, and extending decurrently below and marginally a short 

 distance above; perichaetial leaves erect, straight, long, plicate, sheathing: 

 seta variable, but usually 2-3 cm high; capsule cylindric, arcuate, orange-red, 

 darker when old, when dry and empty somewhat constricted below the mouth, 



