104 American Midland Naturalist Monograph No. 6 



ments; operculum conic to convex, rostrate; calyptra campanulate, plicate, 

 covering most of the urn, glabrous, hirsute or papillose. 



A cosmopolitan genus of about 200 species, on trees or rocks, rare, however, 

 in the Tropics; about 60 species occur in North America; at least 5 in our 

 region. 



Key to the Species 



A. Peristome simple, teeth 16, erect or erect-spreading when dry B 



A. Peristome double, teeth more or less reflexed when dry D 



B. Capsule half-emergent, 16-striate (O. cupulatum [Hoffmann] Schwaegrichen) 



B. Capsule immersed to half-emergent, 8-striate C 



C. Capsule ovate-cylindric, half-emergent when leaves are dry 1. O. strangulatum 



c. Capsule much shorter, ovate-globose, practically immersed in the dry leaves 



2. O. Lescurii 



D. Capsule smooth when dry, immersed E 



D. Capsule plicate when dry F 



E. Teeth 16, in pairs; segments 8, short, filiform ( O. pusillum Mitten) 



E. Teeth 16, not in pairs; segments 16, comparatively broad 



(O. elegans Hooker & Greville) 



F. Leaves more or less obtuse at the extreme apex G 



F. Leaves usually distinctly acute at the extreme apex ! 



G. Capsule strongly contracted below thg mouth when dry and very decidedly plicate 



with reddish-brown folds 3. O. stellatum 



G. Not very strongly contracted nor very decidedly plicate H 



H. Stomata immersed; leaf-margins revolute 4. O. ohioense 



H. Stomata not immersed; leaf-margins erect; leaves short and broad, oblong-ovate to 



lingulate, obtuse, usually with brood-bodies 6. O. obtusijolium 



I. Capsule but little contracted below mouth when dry, ribs orange, segments 8; leaves 



oblong-lanceolate 5. O. pumilum 



I. Capsule strongly contracted under the mouth when dry J 



J. Capsule with very prominent reddish-brown ribs when dry, half-emergent 



3. O. stellatum 



J. Capsule with less prominent light colored ribs, usually immersed (or emergent) 



(O. sard dum Sullivant) 



L Orthotrichum strangulatum Schwaegrichen 



(O. Porteri Austin; O. cupulatum var. Porteri Venturi) 



Plate XVIII 



Densely cespitose, about 1 cm high: stems densely leaved, branched; upper 

 leaves lanceolate, about 3 mm long, the lower ovate, shorter, acute, margins 

 entire or papillose, more or less revolute, lamina often somewhat bi-stratose 

 at margins and apex; costa strong, almost percurrent; basal leaf-cells quadrate 

 at margin to rectanoular (2:1) towards costa, smooth, hyaline, the median 

 rounded-hexagonal, dense, papillose, becoming towards apex densely incrassate- 

 rounded, arranged in quite regular rows: seta short, about 0.5 mm, capsule 

 about 1.5 mm long, oblong-cylindric, tapering rather gradually to the seta, 

 when dry often only partly immersed, when wet always immersed, dark reddish- 

 brown, deeply 8-costate and 8-furrowed, the costae with about 3 rows of rectan- 

 gular cells with thicker longitudinal walls, stomata few, immersed, calyptra 

 mitrate, quite densely erect-hirsute; operculum low with a rounded apiculation; 

 peristome single, teeth paired, papillose, erect-spreading when dry, irregularly 



