JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 150.131.192.151 on Sun, 05 Apr 2015 12:49:50 UTC All use subject to JSTOR Terms and Conditions Abstract. The checklist includes a listing of the genera and species of North American mosses thought to occur in the continental United States and Canada. The floras of Mexico and Greenland are not included. The list for Sphagnum is in an accompanying paper. Including Sphagnum, 1,320 species and 109 varieties are recognized in 312 genera and 72 families. Accompanying the list are a systematic arrangement of the genera, species, and varieties, and a list ofsynonyms and excluded species. Three nomenclatural changes are made: Limprichtia cossonii (Schimp.), comb. nov., Polytrichum papillatum (G. L. Sm.), comb. nov., and Schistidium heterophyllum (Kindb. in Mac. & Kindb.) McIntosh, comb. nov. The first comprehensive checklist of the mosses of North America north of Mexico was published by Grout (1940), with Andrews (1940) providing a list of Sphagnum species. In 1965, Crum, Steere, and Anderson produced their first checklist which was revised eight years later (Crum et al. 1973). The same three authors began a second revision of the list several years ago, but the effort was interrupted by pressures of other tasks. Shortly thereafter, Bill Steere regrettably withdrew from the project. Several years later Crum and Anderson resumed work on the list. William R. Buck's involvement dates back to his graduate student days at the University of Michigan.Through the years, especially recently, he has contributed enormously to all aspects of the checklist. The senior authors feel that his efforts fully justify their invitation to become a joint author. Thus, with the help of many bryologists throughout the world we present here the long overdue revision.The systematic arrangement of the genera and families, more or less, follows the sequence of Brotherus (1924)(1925). We have shifted several genera and we have made minor rearrangements of families. The current trend in bryology seems to be toward narrower generic and familial concepts, and we have more or less followed this trend. For those who disagree with our usage we have provided the authorities for names listed among the synonyms. The users of the checklist therefore can easily retrieve whatever names they wish.It is next to impossible to construct a checklist that is entirely updated and error free. It is also impossible to make one that will please anyone, even ourselves. Species are unequal in value, even in the same genus, and opinions concerning their limits vary enormously. Notions about generic lim-It is with respect and affection that we dedicate this checklist to our late friend and colleague, William C. St...

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In spite of the more general distribution of many bryophytes, dramatic disjunctions exist, many of them similar to those shown by vascular plants. Various explanations have been offered to explain these disjunctions including continental drift, long-distance dispersal, and the fragmentation of a once more continuous distribution. No single hypothesis is sufficient to accommodate all species within any disjunctive pattern. The most serious difficulty is tlie inadequacy of exploration of considerable areas of the globe.Various bryophyte disjunctions are mapped in 51 distribution maps, and details of sexual patterns and dispersal mechanisms are assessed.Most bryophytes are widely distributed. In the Northern Hemisphere more than 60% of the flora of arctic and boreal regions is made up of the same species.Within this wide range, however, each species has highly specific requirements and some are exceedingly local.Becavise bryophytes have air-borne diaspores their means of dissemination would appear to guarantee a wide distribution of all species. That disjunctions exist at all would seem somewhat anomalous, yet such disjunctions do exist, some of them very dramatic. The explanation of these disjunctions has led to numerous intriguing hypotheses, many of which have been derived from similar studies of flowering plant disjunctions.In North America tlie disjunctions that have received the greatest attention

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