18 American Midland Naturalist Monograph No. 6 



at or beyond the middle of the hii\ cells rarely linear, mostly quadrate and 



parenchymatous, or hexagonal and short-prosenchymatous 



Amblystegium, p. 218 



109. Aquatic; leaves mostly short and broad, rojnJed and LLint, soft; median leaf- 

 cells linear-vermicular, the alar forming a distinct group, sub-rectangular or 



somewhat inflated Hygrohypnum, p. 243 



109. Not with the above combination of chnracters 110 



110. Leaf-cells narrowly linear; leaves broadly ovate to cordate or lanceolate, 



prolonged into awl-shaped reflexed squarrose tips Campylium, p. 247 



110. Not with above combination of characters HI 



111. Leaves oval- to oblong-lanceolate, more or less long acuminate; leaf-cells nar- 

 row, prosenchymatous; plants shining Homomallium, p. 225 



111. Not with characters combined as above 112 



112. Plants very slender, not shining; leaves usually spreading in all directions, 

 lanceolate to linear-lanceolate; cells rhomboidal to long hexagonal, 2 to 



4, or rarely 6-8, times as long as broad Amblystegiella, p. 223 



112. Leaf-cells prolonged-linear, mostly very narrow 113 



113. Leaves erect-spreading or imbricated, oblong-ovate to nearly circular, obtuse or 



apiculate, often very concave; costa short and double, or none 



Calliergonella, p. 242 



113. Leaves more or less falcate-secund to circinate, from a mostly narrowed and 

 somewhat decurrent base, becoming ovate- to triangular- or cordate-lanceo- 

 late, more or less slenderly acuminate; cost^ weak and reaching above the 



middle, or rarely even excurrent Drepanocladus, p. 235 



1 14. Paraphyllia numerous; leaves more or less concave, from abruptly to 



gradually acuminate, mostly plicate Hylocomium, p. 255 



1 14. Paraphyllia none or few 115 



1 15. Stem-leaves more or less squarrose-spreading to falcate-secund, acuminate 117 



1 15. Stem-leaves more or less crowded, imbricate but with more or less spreading 



or secund tips 116 



1 15. Stem-leaves elliptic, concave, apex obtuse; branches julaceous Hypnum, p. 258 



1 16. Stem-leaves turgidly imbricate and secund, rugose, narrowly lanceolate- 

 acuminate from a broadly oblong base, glossy; apex distinctly serrate; 



cilia two; annulus present Rhytidium, p. 254 



1 16. Stem-leaves close or loosely imbricate, not secund, broadly ovate or 

 rounded with an obtuse apex, olive or grayish-green, ap>ex faintly crenu- 



late; cilia three; annulus none Hypnum, p. 258 



116. Leaves broad, obtuse, concave; alar cells inflated Calliergonella, p. 242 



117. Alar cells not at all or but very little differentiated; plants distantly and 



irregularly pinnate; leaves squarrose or spreading-secund 



Rhytidiadelphus, p. 252 



117. Alar cells distinctly differentiated; plants closely pinnate; leaves circinate- 



secund Ctenidium, p. 25 1 



118. Plants large, to 15 cm, closely and regularly pinnate leaves linear-acumini- 

 nate from a broadly ovate base, stem-leaves plicate, falcate-secund; 

 cilia 3 or 4 Ptilium, p. 259 



118. Plants large to quite slender, simple or pinnate, mostly irregularly pin- 

 nate; leaves ovate- to cordate-lanceolate, shortly to slenderly acuminate, 

 generally circinate-secund in two series Stereodon, p. 260 



1 18. Characters not combined as above 128 



1 19. Leaf-cells very narrowly prosenchymatous, alar cells mostly not differentiated; 

 leaves oblong to linear, short (winted, or ovate- to linear-hnceolate, acute to 



long-acuminate or piliferous hopterygium, p. 269 



1 19. Leaf-cells not so narrow, alar cells mostly broader, hyaline and thin-walled; 

 leaves broadly lanceolate to oval, more or less long-acuminate, decurrent 

 Plagiothecium, p. 274 



