Notes on the Rare Moss Exobryum fragilicuspis (Pottiaceae, Bryophyta) in North America

Abstract

The moss Exobryum fragilicuspis (Broth.) R.H.Zander is reported from the Rocky Mountains of Alberta, Canada, in Jasper National Park. The species is synonymous with several previously recognized taxa, including Didymodon fragilicuspis Broth., Didymodon gaochienii B.C.Tan & Y.Jia, Didymodon murrayae Otnyukova, and Vinealobryum murrayae (Otnyukova) R.H.Zander. Exobryum fragilicuspis is distinctive in having specialized caducous propagules with barrel-shaped segments at the leaf apices. These detach readily and cause the apices of developed leaves to appear broken. Despite these distinctive features, the species is rarely reported in North America, where it was previously known from three sites in Alaska and British Columbia. The collection from Alberta is the most recent in 30 years in North America, and provides new insights into the species' distribution and ecology. Features of Exobryum fragilicuspis are compared to other related species from North America.