Abstract
Drepanocladus crassicostatus Janssens is described as new from North American collections of living populations and from fossils of Pleistocene and Holocene age. The species is compared with D. capillifolius (Warnst.) Warnst., D. exannulatus var. rotae (De not.) Loeske, D. exannulatus var. purpurascens (Schimp.) Herz. and D. trichophyllus (Warnst.) Podp. Drepanocladus crassicos- tatus is differentiated from these mosses by less well-developed groups of alar cells, a strong, wide costa, and the absence of brush-like branch tips. It is known only from western North America and occurs in more minerotrophic habitats than D. trichophyllus. Evidence for the occurrence of D. trichophyllus in North America is a single collection. Many late Tertiary and Quaternary sediments in glaciated and periglacial areas of North America are particularly rich in bryophyte remains. Fragments of mosses can be extracted from fluviatile, deltaic, and lacustrine sediments, in addition to peats. The specimens are not substantially altered by diagenetic processes and most can be handled by the same techniques as are used with specimens of living bryophyte populations. Late Cenozoic bryophytes in North America can all be referred to extant moss taxa, and the distinct microscopic features of the leaves make it possible to identify most frag- ments to species level. Miller (1980) listed 725 records in his catalogue of Quaternary fossil bryophytes of North America. In addition, approximately one thousand bryophyte records from Pleistocene and Holocene sediments have been accumulated in the course of my work on Alaskan, Yukon, and other sediments from the Arctic Archipelago and on Min-
Published Version
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