| Summary: | This investigation presents a bryo-geographical study of the Alexander Archipelago and the adjacent mainland of southeastern Alaska. A flora containing the 572 taxa of hryophytes now known from southeastern Alaska (67.5 percent of the known Alaskan bryoflora) has been compiled from published records and 10,901 collections made by the author. These specimens were obtained from 130 sites during an accumulated field time of 40 weeks from 1966 through 1969. There are included 38 taxa new to the state and 94 which are new to southeastern Alaska. The local distribution of each taxon has been cited fully either within the text or as a distribution map. Habitat, biological, taxonomic, and distributional information are given for each entry. The most significant components of the flora are treated within 27 geographical elements. There are probably no bryophytes endemic to southeastern Alaska. Of the total bryoflora, taxa with widespread distributions comprise ca. 74 percent, northern Pacific Basin taxa constitute ca. 16.8 percent (over one half of these are western North American endemics), ca. 5.4 percent of the flora belongs to the western North American - western Eurasian disjunction, and ca. 3.8 percent of the total displays less distinct or individual distribution patterns. The regional flora is not particularly distinctive, is com posed primarily of broad endemics or plants of widespread ranges, and is a portion of the cool-temperate, oceanic geographical zone that extends from the northern Gulf of Alaska to Vancouver Island. Southeastern Alaska lies within the northern portions of the principal zone of western North American endemism. The bulk of the flora is of temperate, cool temperate, and boreal origins with exceedingly few taxa having tropical, subtrop-cial, or arctic affinities. It has been derived primarily from a widespread Arcto-Tertiary flora which has been dissected and has re-expanded with the fluctuating events of the Pleistocene. Taxa of the North Pacific Arc represent a diversity of distributional patterns which tends to favor a recent history of post-Pleistocene expansion from local rather than from trans-Pacific sources. Several taxa, primarily hepatics of hyperbeeanic habitats, display disjunct ranges wherein certain local populations are postulated to be essentially relict. Local refugia of undetermined age exist on the elevated marine terraces northward from Icy Point to the vicinity of Yakutat Bay. Mountain nunataks were not probable as important refugia during maximum glaciations, but seaward headlands of the outer islands, strandflats, and exposed portions of the continental shelf also may have served as refugia and supported diverse communities. A zone of significantly wetter climate extends along the outermost coast and adjacent to the Dixon Entrance. Over three percent of the local flora (mostly hepatics) are restricted to the zone and are diagnostic of that environment. Areas of drier climate occur within rainshadow zones of the archipelago, along the continental Boundary Ranges, and in the upper Lynn Canal complex. The last region may he especially sensitive to climatic change and an immigration route between the oceanic and continental floristic areas. Relict populations of bryophytes (primarily mosses) from Hypsithermal time persist in specialized habitats in the archipelago within the drier zone. Science, Faculty of Botany, Department of Graduate
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