HYPNACEAE I07 



leaves usually much alike, ovate to ovate-lanceolate or oblong- 

 lanceolate, little concave, margins usually plane; differentiated 

 alar cells few (except in striatelliim and latebricolor) ; median cells 

 long, linear-flexuose to linear-rhomboidal; costa lacking, or short 

 and double, or forking. Capsules oblong-ovoid to cylindric, 

 usually inclined and more or less unsymmetric (except latebricolor 

 and laetum). 



P. striatellum, because of squarrose leaves and inflated alar 

 cells, is likely to be sought under Campylium. Hypnum pra- 

 tense forms are apt to be sought under Plagiothecium because of 

 the complanate leaves. The two subgenera are, by many 

 authors, treated as separate genera, and there are good reasons 

 for so doing, but in a work of this kind conservatism is believed 

 to be most helpful. 



Key 



Mostly very slender plants, light yellowish green to whitish, glossy; 

 leaves little or not at all decurrent; median leaf cells narrowly 

 linear, alar little or not at all differentiated; capsules not plicate 

 (except in turfaceum) Isopterygium 



Usually larger, darker green; leaves decurrent; leaf cells wider; alar 



clearly differentiated; capsules often plicate Euplagiothecium 



Isopterygium Mitt. 



I — Leaves entire, scarcely a trace of serration on any leaf; cortical cells 

 of stem very large; plants of cold ravines, growing mostly in moist 



crevices of ledges Muellerianum 



Leaves (some or all) more or less serrate 2 



2 — Leaves strongly serrate in the upper half 3 



Leaves serrulate at or near apex only 6 



3 — Plants very slender, usually growing on decayed wood or humus, 



sometimes on soil 5 



Plants largest of the subgenus, resembling Euplagiothecium, growing 



on earth and stones 4 



4 — Plants dark green; leaves distant, apex usually bluntish as in 



Eurhynchium Mans geophilum 



Plants lighter green, usually yellowish and glossy; leaves closer, not 



blunt deplanatum 



5 — Leaves short-acuminate; capsule not striate; operculum rostrate. .Groutii 

 Leaves long and slenderly acuminate; capsules somewhat striate 



when dry and empty; operculum conic turfaceum 



6 — Plants light yellowish-green; costa very faint or none; growing 



chiefly in the lowlands from Long Island southwards micans 



