Jennings: Manual of Mosses — 31. Hypnaceae TT^ 



hyaline-bordered, the divisural zigzag, the teeth dorsally cross-striate, numer- 

 ously lamellate; lid convex-conic, acute to rarely rostrate. 



A genus of about 70 species, mostly growing on rocks and stones, rare in 

 the tropics; about 17 species in North America; at least 4 species in our region. 



Key to the Species 



A. Leaves spreading more or less uniformly in all directions B 



K. Leaves distinctly complanately disposed C 



B. Leaves erect-spreading; alar cells not inflated 2. P. Roeseanum 



B. Leaves squarrose, more or less serrulate; alar cells inflated L P. striatellum 



C. Costa forked, often reaching to the middle of the leaf; capsule usually striate when 



dry 3. P. sytvaticum 



<:. Costa thin, short and double, or none; capsule usually smooth when dry; lid conic 

 to short-rostrate 4. P. denticulatum 



1. Pl.agiothecium striatellum (Bride!) Lindberg 



(Hypnum MuehlenbeckH Schimper; Plagiothecium Muehlenbeckit 

 Bryologia Europaea; Leskea striatella Bridel) 



Plate LI 



Slender, dense, dark green, lustrous: stem prostrate, branches crowded, 

 erect or ascending, straight or slightly curved; leaves about 1-1.3 mm long, 

 crowded, sub-complanate, the branch-leaves squarrose-spreading, ovate-lanceo- 

 late or triangular-lanceolate with a long slender and flexuous acumen, plane- 

 margined, serrulate above at least, the base strongly decurrent: costa double 

 and faint; median leaf-cells linear-fusiform, flexuous, rather short, about 6- 

 10:1, the basal somewhat larger, the alar abruptly very much enlarged, inflated, 

 hyaline to colored, and forming the much decurrent and plainly distinct 

 auricles; inner perichaetial leaves half-sheathing, the apex filiform- flexuous and 

 usually recurved: capsules about 2 mm long, slightly curved, oblong-cylindric 

 with a tapering neck, distinctly striate when dry; lid conic, rather obtuse; 

 annulus large, compound; exothecial cells minute and rounded in three to five 

 series at the rim, below rapidly becoming irregularly oblong and more or less 

 incrassate; teeth short, yellowish, papillose above, dorsally cross-striolate below, 

 lamellate, strongly trabeculate, slightly confluent at base; segments about as 

 long, slender, pale, granulose, only slightly carinate cleft; basal membrane only 

 about one-fourth to one-third as high as the teeth; the cilia 1 to 3, a little 

 shorter than the segments; spores mature in late spring or early summer, 

 yellowish, papillose, rather incrassate, .007-.010 mm. 



On earth, rocks, and rotten logs, in woods, usually in non-calcareous habi- 

 tats; Europe, and from Arctic America south to North Carolina. 



Butler Co.: One mi. e. of Mercer Road Sta. C.M.B. Oct. 4. 194L Cambria 

 Co.: Ebensburg. T. P. James. (Porter's Catalogue). Favette Co.: Cucumber Falls, 

 Ohiopyle, June 22, 1940, and Laurel Run, Chestnut Ridge, Dunbar Twp., June 16, 

 1940. C.M.B. Lawrence Co.: Slippery Rock Creek, 1906. Miss Susan Gageby. Mc- 

 Kean Co.: On sandstone rocks, Rutherford Rocks, altitude 2000 feet, July 7, 1894, 

 Divide between Hawkins and Rutherford Hollows, April 25, 1893, and March 12, 1894, 

 and Langmade. May 9, 1896 (figured). All near Bradford. D.A.B. 



