50 ORTHOTRICHACEAE 



consists of 16 rather short teeth, which are nearly always reflexed 

 when dry and are often united in pairs; the inner peristome is 

 usually represented by 16 slender hairlike processes, often called 

 cilia, but really homologous with the segments of the type of 

 peristome found in Mnium and Hypnum. In some cases the 

 peristome may be simple or even wanting, as in Amphidium. 

 This family is often united with the Grimmiaceae, from which 

 it is distinguished by the italicized characters. Members of 

 these two families may become so dry and brittle as to crumble 

 to dust in the fingers and yet retain their vitality unimpaired, 

 springing into renewed growth with the next rain. 



Key to the Genera 



i — Calyptra smooth, cucullate; peristome none or very short and 



single; rock-growing except Drummondia 2 



Calyptra mitrate, nearly always hairy; peristome well developed, 



almost always double; growing almost exclusively on trees 3 



2 — Tree-growing; capsule long-exserted; peristome single, short and 



truncate. Common Drummondia 



Rock-growing; capsule barely exserted; peristome lacking . ..Amphidium 



3 — Capsule exserted; leaves crisped, except U. Americana Ulota 



Capsule immersed or emergent; leaves not crisped when dry. 



Orthotrichum 



AMPHIDIUM (Nees) Schimp. (Amphoridium and Zygodon 



of authors) 



Slender-stemmed dichotomously branching plants growing on 

 rocks, usually in dense tufts from 3-8 cm. in depth, rather 

 densely radiculose. Leaves linear to lance-linear, twisted and 

 contorted to crispate; costa strong, reaching nearly to apex; 

 upper leaf cells small, thick- walled, rounded or angular, said to 

 be papillose but the papillae are very low and inconspicuous; 

 basal cells becoming gradually elongated-rectangular and thin- 

 ner walled, also lighter colored or even hyaline. Calyptra 

 cucullate, without hairs. Capsules erect, emergent or exserted, 

 with a distinct neck, becoming urn-shaped and 8-striate when 

 dry; peristome none. 



Both species mature their spores in summer. 



Autoicous; leaf margins plane; seta 1.5 mm. long or less lapponicum 



Dioicous; leaf margins recurved below; seta about 3 mm. long. . . .Mougeotii 



