POTTIACEAE 107 



similar capsule is Physcomitrium, which is a little larger 

 and more common than Pottia. It also has short stems 

 and leaves similar in shape, but lighter colored; the 

 seta is longer and the capsule is larger, lighter colored, 

 and more urn-shaped; that is, with the outline more 

 curved. See illustration of Physcomitrium (p. 122). 

 Weisia (p. 100) resembles Pottia in size, but the leaves 

 are hair-like and the capsule is cylindrical and more 

 slender than that of Pottia. 



17. TORTULA Hedw. (Tor-tu-la) 



A large genus widely distributed. But two species 

 are described here, and they are very rare. Name 

 derived from the Latin for " twisted," referring to the 

 peristome. 



Plants growing close together on rocks and on trees in 

 dense cushions or patches; light or dark green; fruit some- 

 times abundant in T. muralis. 



Stems erect, short, about /4 inch long, or less. 



Leaves broad and short in T. papulosa; longer in T. 

 muralis, with the midrib extending beyond the leaf in a 

 hair-like tip, not easily seen without a lens; only slightly 

 crisped when dry; light or dark green. 



Seta in T. muralis about H inch long; yellowish to reddish. 



Capsule in T. muralis long-cylindrical, erect; yellowish 

 or reddish; mature in spring. 



Peristome twisted as in Tortclla (p. 102) and Barhula 

 (p. 105). Seen with a lens. 



Operculum long-beaked. 



