nw North America, e Asia, temperate regions.
The family Pleuroziopsaceae was established solely for the genus Pleuroziopsis (R. R. Ireland 1968), primarily because of the unique stem lamellae first reported by A. Noguchi (1952b). The lamellae are abundant on the branches and branchlets and, in addition to being attached to the stems, they are attached to the abaxial surface of the leaf bases and proximal costa. The pinnate and 2-pinnate branching pattern, the ovoid, arcuate, cernuous capsule with hypnaceous peristome, and the absence of paraphyllia are additional morphological characters distinguishing this genus from Climacium. Recently, D. H. Norris and M. S. Ignatov (2000) discovered (1–)2–3-stratose longitudinal streaks (stem lamellae) on the stems of C. dendroides growing intermixed with Pleuroziopsis from. These lamellae are scattered along the stems of C. dendroides, the only species of Climacium in which they were observed. Whether or not these lamellae are morphologically similar to those of Pleuroziopsis is debatable. The lamellae of Pleuroziopsis, which are numerous, are attached to the leaf bases, the costa, and the epidermal cells of the branch and branchlet stems, continuing proximally toward the leaf below. The lamellae of C. dendroides are not attached to the leaf bases or costa, only to the epidermal stem cells. In addition to the lamellae, the authors noted that the structures referred to as paraphyllia in Climacium are actually rhizoids, just as they are in Pleuroziopsis. It is primarily because of stem lamellae that the authors believe Pleuroziopsis should be placed back in Climaciaceae. Capsules of Climacium and Pleuroziopsis are quite different (Ireland). The value at the familial level is not as important, since reduced peristomes are known to occur in some families of pleurocarpous mosses, as Ignatov et al. (1998) have pointed out for Brachytheciaceae.