88 American Midland Naturalist Monograph No. 6 



sinuate-denticulate margin, or plane and entire; costa more or less excurrent- 

 cuspidate; upper cells short-rhombic, below rhomboidal, dorsally strong thick- 

 ened, smooth, rarely with a few high papillae, the lowest thin-walled, hyaline 

 and rectangular: seta very short; capsule sub-globose, cleistocarpous, immersed; 

 calyptra very small and delicate, conic-mitriform 3-5-cleft; spores small, brown, 

 subglobose, minutely granulose. 



A widely distributed genus, on soil, mostly in the temperate zone. Fifteen 

 species in all, 3 in North America, 2 in our region. 



Key to the Species 



A. Uppermost and perichaetial leaves sharply carinate; costa strongly excurrent 



1. A. triquetrum 



A. Uppermost and jserichaetial leaves concave; costa rarely excurrent 2. rufescens 



1. AcAULON TRIQUETRUM (Spruce) C. Mueller 



{Sphaerangium triquetrum Schimper) 



Plants minute, about 1 mm high, bulbiform, pale green or yellowish, dis- 

 tinctly triquetrous; protonema green, persistent; lower leaves small, rounded, 

 the middle leaves larger, broadly ovate, deeply concave, convolute, the upper 

 largest (perichaetial) broadly ovate, deeply carinate, triquetrous, all upper 

 leaves with reflexed margins, erose-denticulate above; costa strong, in upper 

 leaves excurrent in a recurved apiculus; basal leaf-cells elongate-hexagonal, 

 lax, thin-walled, hexagonal to ob long- hexagonal : seta about as long as capsule, 

 arcuate; capsule globose, smooth; calyptra minute, mitrate, cleft-lobed, cover- 

 ing only very apex of capsule; spores papillose, about .025-. 030 mm, mature 

 in early spring. 



On clayey or sandy soil in fields or on banks, Europe, Algeria, and, in 

 North America, from v/estern Canada to New England south to the Caro- 

 linas; occurs in Ohio and in Pennsylvania but not yet reported from our range. 



2. AcAULON RUFESCENS Jaeger 



(Phascum rufescens Kindb. ) 



Plants minute, bulbiform, about 1 mm high, yellowish-green, not markedly 

 triquetrous: protonema persistent; lower leaves very small, ecostate, the upper 

 much larger, broadly ovate^ deeply concave, convolute, plane-margined, erose- 

 denticulate at apex; in larger leaves the costa thick, excurrent into a squarrose- 

 recurved apiculus; leaf -cells about as in A. triquetrum: seta flexuose or arcuate; 

 capsule globose, smooth; calyptra and spores similar to those of A. triquetrum. 



On bare clayey or sandy soil in moist fields, eastern and central North 

 America. 



Indi.ana Co.: Derry. James. (Porter's Catalogue, as Sphaerangium muticum [Schre- 

 ber] Schimper). 



10. Phascum [Linnaeus] Hedwig 



Autoicous or synoicous: very small, closely gregarious: stem short, without 

 central strand, erect, simple or bushy-branched; leaves mostly ovate-lanceolate 

 to elongate-lanceolate, mostly with entire and revolute margins, the upper 



