90 American Midland Naturalist Monograph No. 6 



1. PoTTiA TRUNCATa [Hedwig] Fuernrohr 



(P. truiicatiila Lindbsrg; GymnoUomum truncjtum Hedwig) 



Plate XVII 



Densely cespitose, dull green: stems simple or sparingly branched, erect, 

 about 2.5 mm high, radiculose at base; leaves numerous, the upper much larger 

 than the lower, obovate to oblong-spatulate, about 1.5-2.5 mm long, soft, 

 spreading, the margins plane, minutely crenulate with the projecting trans- 

 verse cell-walls, the leaves when dry become twisted, apex abruptly acute, costa 

 strong and excurrent into a short point; basal leaf-cells quadrate to rectangular, 

 large, lax, hyaline, more or less inflated, above becoming gradually smaller, 

 the median and upper medium- to thin-walled, smooth, hexagonal: seta erect, 

 about 3-4 mm high, mostly yellowish; capsule broadly oval or turbinate, erect, 

 symmetric, about 0.6-0.8 mm high, exannulate, more or less castaneous, when 

 dry and empty smooth and turbinate-hemispheric; lid broadly convex to flat- 

 tish with a beak about one-half as long as the urn; exothecial cells medium- 

 walled, castaneous, pellucid, irregularly quadrate to rectangular, the upper two 

 or three rows at the rim much smaller, rounded-quadrate, obscure; spores 

 orange-pellucid or brownish-pellucid, minutely punctulate, large, .026-030 mm, 

 mature from autumn to spring. 



On moist soil in grasslands, along streams, etc., Europe, Asia, northern 

 Africa, and from Ontario to New England and Maryland, Pennsylvania, 

 and Michigan. 



Rare in our region. McKean Co.: Corydon Street, Bradford. D.A.B. (figured). 



12. Desmatodon Bridel 



Autoicous: slender plants in mostly low, soft, green to yellow-green tufts, 

 dense to loose: stem mostly with central strand, thickly foliate, forking; leaves 

 when dry appressed and more or less plicate, when moist erect-spreading, cari- 

 nate to concave, obovate to ovate or lance-linear, mostly with recurved mar- 

 gins below, plane above, often serrate, sometimes margined; costa ending below 

 the apex or less often mucronately or aristately excurrent; leaf-cel's loose, thin- 

 walled, above rounded-quadrate or more or less hexagonal or rhomboidal, 

 mammillose to papillose, below rectangular and long-hexagonal, hyaline, smooth: 

 seta elongate, mostly straight; capsule erect, inclined, or even pendent, mostly 

 symmetric, ovate to cylindric; annulus persistent or falling away in pieces; 

 peristome inserted below the rim of urn, the basal membrane forming a tube 

 which is slightly exserted from the urn, thickly articulate, the 16 teeth rather 

 broad, divided to the base into two or three flat, filiform, papillose, divisions, 

 united here and there, usually twisted; lid stoutly and obliquely rostrate, with 

 the cells more or less spirally arranged; calyptra cucullate, smooth, long- 

 rostrate; spores large. 



A. genus of 8 species, mainly on rich humus-soil in the mountains or on 

 mostly limestone rocks; one species in our re2ion. 



Key to the Species 



A. Costa of at least the upper leaves excurrent into a long smooth point 



- (D. piimhobius) 



