40 TORTULACEAE 



of cells, costa strong; basal cells usually thin-walled, hyaline 

 and rectangular; upper cells usually thick-walled, quadrate to 

 subcircular, papillose. Seta straight; calyptra cucullate, smooth, 

 capsule erect and symmetric or nearly so; cleistocarpous, gym- 

 nostomous, or, usually, peristomate; peristome when present 

 of 1 6 straight or spirally twisted teeth which are often divided 

 into two filiform papillose divisions, appearing as if there were 

 2,2 teeth. 



Key to the Genera 



i — Leaves widest at or near base, usually tapering to an acute apex. . 4 

 Leaves increasing in width from the base upwards, usually broad 

 in outline and rounded at the apex except for the excurrent costa 



(some forms of Barbula ungidculata may be sought here) 2 



2 — Peristome lacking (in our species) 12 



Peristome present (very short in some species of Desmatodon) 3 



3 — Costa strongly excurrent into a hair point; peristome of 32 filiform 



teeth from a high basal membrane, twisted to the left Tortula 



Costa not excurrent (except in D. plinthobius) ; peristome teeth 16. 



Desmatodon 



4 — Plants minute; cleistocarpous 5 



Plants larger; capsule opening by a lid; peristome lacking or present. . 6 

 5 — Areolation dense and strongly papillose above; upper leaf margin 



strongly involute Astomum 



Leaves more loosely areolate, margin slightly revolute above. .Phascum 



6 — Peristome lacking; leaf margins plane or revolute Gymnostomum 



Peristome lacking; leaf margins involute (forms of) Weisia virdula 



Peristome present 7 



7- — Leaves with margin more or less revolute (scarcely so in Barbula 

 convoluta), curled or occasionally crisped when dry; basal cells 



rarely hyaline, usually yellowish or reddish 8 



Leaves with margin plane or involute; basal cells mostly hyaline; 



costa often excurrent ; leaves usually crisped when dry 9 



8 — Peristome teeth 16, more or less divided or perforate along the 



median line, erect or twisted to the right Didymodon 



Peristome teeth 32, filiform, strongly twisted to the left Barbula 



9 — Leaf margin strongly involute Weisia viridula 



Leaf margin plane or leaves concave 10 



10 — Basal leaf cells hyaline, elongated-rectangular and extending 



obliquely up the margin; peristome of 32 long twisted teeth. Tor tella 

 Basal cells not as above, or, if so, not extending up the margin; 



peristome of 16 untwisted teeth (in our species) II 



1 1 — Leaves as in Tortella, except that the hyaline cells do not extend up 



the margin Trichostomum cylindricum 



