Gradstein, S. R., S. P. Churchill and N. Salazar-Allen 2001. Guide to the Bryophytes of Tropical America. NYBG Press. Recent coverage of moss and liverwort genera in tropics of western hemisphere, including excellent descriptions, keys, illustrations, and references to current taxonomic literature.
 

Zander, R. H. 1993. The Genera of the Pottiaceae: Mosses of Harsh Environments. Bull. Buffalo Soc. Nat. Sci. 32:1-378. An indispensible reference for work on this large and taxonomically difficult family of mosses.

Crum, H. A. and L. E. Anderson 1981. Mosses of Eastern North America, Vols. I & 2. Columbia University Press. The best bryoflora coverage available in North America. Most of the taxa treated also occur in the PNW: indispensible for taxonomic notes, descriptions, and illustrations.

Sharp, A. J., H. Crum, and P. M. Eckel 1994. The Moss Flora of Mexico, Vols. I & 2. NYBG Press. Covers a significant component of the bryoflora of western North America.

Flowers, S. 1973. Mosses: Utah and the West. Brigham Young University Press. Though somewhat nomenclaturally dated (and out of print), descriptions, keys and illustrations are a useful resource.
 

Paton, J. A. 1999. The Liverwort Flora of the British Isles. Harley Books. A concise (626 pp.) treatment with good keys, illustrations, and descriptions. Since many liverworts are circumboreal this flora is useful in our region, though there are many differences between the two regions.

Frye, T. C. and L. Clark 1937-1947. Hepaticae of North America. U. Washington Pub. Biol. 6 (1-5): 1-1022. Out of date and out of print, but still a useful reference (if you can find it).

Nash, T. H. 1996. Lichen Biology. Cambridge University Press. Thorough review of current research in lichen biology and excellent summary of what is known: morphology, physiology, ecology, systematics.

Esslinger, T. L. and Egan, R. S. 1995. A sixth checklist of the lichen-forming, lichenicolous, and allied fungi of the continental United States and Canada. Bryologist 98(4) 467-549. The checklist is now updated regularly on the internet (http://www.ndsu.nodak.edu/instruct/esslinge/chcklst/chcklst7.htm). The extensive bibliography is also updated.

Goward, T., B. McCune and D. Meidinger 1994. The Lichens of British Columbia, Part 1 - Foliose and Squamulose Species. Ministry of Forests Research Program.

Goward, T. 1999. The Lichens of British Columbia, Part 2 - Fruticose Species. Ministry of Forests Research Program. These volumes, which are downloadable (free), provide excellent illustrated keys to the macrolichens of PNW and include many arctic/alpine species likely to be found in our region.

Thomson, J. W. 1984. American Arctic Lichens, 1. The Macrolichens. Columbia University Press.

Thomson, J. W. 1997. American Arctic Lichens, 2. The Microlichens. University of Wisconsin Press. Descriptions, keys, photographs and illustrations to Arctic species, but very useful for for the alpine lichens of our region.

Purvis, O. W., B. J. Coppin, D. L. Hawksworth, P. W. James and D. M. Moore 1992. The Lichen Flora of Great Britain and Ireland. British Lichen Society. Excellent keys and descriptions, useful for many species in our region. Especially valuable for it’s coverage of microlichen genera.

Recent Literature on Lichens, a series published in The Bryologist, a journal of The American Bryological and Lichenological Society, listing all recently published papers in lichenology. A searchable database is available on the internet:
(http://www.toyen.uio.no/botanisk/bot-mus/lav/sok_rll.htm)
 

Vitt, D. H., J. E. Marsh, and R. B. Bovey 1988. Mosses Lichens and Ferns of Northwest North America. Lone Pine. This compact little field guide contains concise introductions to morphology as well as ecology and methods of study. The keys are helpful, though incomplete for our area. The pictures provide an excellent introduction to many of the common species, but cannot be relied on for positive identification. A brief bibliography provides additional sources for serious students beginning study.