THE BRYOLOGIST 



Vol. XX November, 19 17 No. 6 



THE RHACOMITRIUMS OF WESTERN NORTH AMERICA 



T. C. Frye* 



The genus Rhacomitrium has given more or less trouble in regard to the 

 identification of the western species because a number have been described 

 insufficiently, sometimes no drawings were made to show what the descrip- 

 tion was based on; and because a number of species usually recognized as such 

 are quite close in their approach to each other. It is hoped that this may prove 

 to be of value to those who find difficulty with western material: 



RHACOMITRIUM 



Plants mostly branched. Stem without central strand, with rhizoids only 

 at base. Leaves with or without hyaline point, lanceolate; vein extending to 

 tip except in R. palmeri, margin mostly entire except the hyaline point; surface 

 often sunken over the cell-cavities or over the walls. Cells strongly sinuose, 

 the lower usually elongated, the upper isodiametric to elongated. Dioicous. 

 Calyptra mitrate, rather long-beaked. Seta straight or curved, twisted to the 

 right or left. Capsule oval to cylindric, smooth, with stomates. Lid conic, 

 with long beak; beak 3^ to once the length of the capsule-body. Annulus pres- 

 ent. Peristome single; teeth divided to below the middle into 2-3 divisions, 

 with swollen joints. (Gk. rAa^05= frayed, mitrion=a. cap; referring to the fringed 

 calyptra.) 



Key to the Species 

 A. Upper green leaf-cells isodiametric or nearly so. 



B. Hyaline points lacking on all leaves, even on those of the branch-tips. 

 C. Leaves with 2-4 ridges several cells high on the under side of the vein. 



I. R. patens 



CC. Leaves without ridges on the vein. 



D. Leaves distinctly papillose on both sides; seta twisted to the left. 



10. R. canescens 



DD. Leaves not papillose; seta twisted to the right. 



E. Isodiametric leaf-cells restricted to the marginal row above, and 

 to a few cells in the tip; capsule-body 3.3-3.8 mm. long. 



9. R. varium 



EE. Isodiametric leaf cells predominating above except in the vein; 

 capsule-body 2.6 mm. or less long. 



* The writer is indebted to Mrs. E. G. Britton, R. S. Williams. J. W. Bailey, and J. M. Macoun 

 for assistance. 



The September number of the Bryologist was published October 13, 1917. 



