BFNA Title: Pleuroziopsaceae
Robert R. Ireland
Plants glossy, medium-sized to large, in loose to somewhat dense tufts. Stems with a creeping primary stem producing an erect, frondose-dendroid secondary stem, pinnately and bipinnately branched; lamellae on branches and branchlets numerous, 1--4 cells high, attached to epidermal cells of stems and abaxial surface of leaf bases and costa; lamellae cells smooth, hyaline, inflated, thin-walled; rhizoids abundant on primary and secondary stems, whitish or reddish brown, much branched, papillose, those on secondary stems branches and branchlets on apical cells of lamellae, usually dichotomously branched, smooth; paraphyllia and pseudoparaphyllia lacking; Secondary stem leaves complanate to slightly concave, erect, oblong-ovate, apiculate. Secondary stem branch and branchlet leaves erect-spreading, long-decurrent; cells of decurrent regions many, hyaline, inflated; median cells long, vermicular; costae single. Sexual condition dioicous. Seta elongate. Capsule lateral on stem, ovoid, arcuate, cernuous; peristome hypnaceous, double, teeth trabeculate, cilia lacking.
Genus 1, species 1; temperate climates.
The family Pleuroziopsaceae (R. R. Ireland 1968) was established for the genus Pleuroziopsis primarily because of the presence of the unique stem lamellae first discovered by A. Noguchi (1952). 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 part of the costa. Also, the pinnate and bipinnate branching pattern, the ovoid, arcuate, cernuous capsule with a hypnaceous peristome and the lack of paraphyllia were additional morphological characters making it distinct it from Climacium. Recently, D. H. Norris and M. S. Ignatov (2000), discovered (1--)2--3-stratose longitudinal streaks (stem lamellae) on the stems of Climacium dendroides plants growing intermixed with Pleuroziopsis plants from Alaska. These stem lamellae are scattered along the stems of C. dendroides, the only species of Climacium in which they were observed. Whether 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 Climacium dendroides are not attached to the leaf bases or costa but instead only to the epidermal stem cells. In addition to the lamellae the authors noted that the structures referred to as paraphyllia in Climacium are rhizoids, just as they are in Pleuroziopsis. However, it is primarily because of the stem lamellae that the authors believe Pleuroziopsis should be placed back in the family Climaciaceae.
SELECTED REFERENCES Ireland, R. R. 1968. Pleuroziopsidaceae, a new family of mosses. J. Hattori Bot. Lab. 31: 59--64. Noguchi, A. 1952. Mosses of Climaciaceae. Oita Daigaku Gakugeigakubu Kenkyu Kiyo 1: 65--77.
PLEUROZIOPSIS E. Britton, Bryologist 9: 39. 1906 • Pleurozium, a pleurocarpous moss genus; Greek opsis, appearance or likeness
Climacium sect. Girgensohnia Lindberg; Girgensohnia (Lindberg) Kindberg, not Girgensohnia Bunge
1. Pleuroziopsis ruthenica (Weinmann) E. Britton, Bryologist 9: 39. 1906 "ruthenicum"
Hypnum ruthenicum Weinmann, Bull. Soc. Imp. Natural. Moucou 18: 485. 1845; Girgensohnia ruthenica (Weinmann) Kindberg
Plants light green with red secondary stems and branches, green or red branchlets, 4--8 cm, erect, frondose-dendroid, in loose to somewhat dense tufts arising from stoloniferous primary stems matted with whitish or reddish-brown, papillose rhizoids. Secondary stems with pinnate and 2-pinnate branches, branches attenuate, 1.5--3.0 cm, branchlets attenuate, 4--7 mm; lamellae apical cells round, elliptic, square, or rectangular in cross-section, branched rhizoids often arising from the top surface, smooth. Stem leaves clasping stem, 3--4 ´ 1.5--2.5 mm, smooth or wrinkled, ovate, apiculate or obtuse to acute, entire, long-decurrent with many hyaline, inflated cells, 1-stratose, margins plane, costa single, weak, smooth, ending near leaf middle, leaf cells smooth or minutely prorulose, cell walls non-pitted or pits not evident, median cells vermicular, 40--81 ´ 5--7 µm; proximal branch leaves similar to stem leaves, smaller, gradually grading distally into leaves similar to branchlet leaves above; median branchlet leaves 0.5--1.0 ´ 0.3--0.5 mm, plicate, ovate to ovate-lanceolate, broadly acute, irregularly and strongly toothed to serrate from apex to leaf middle, serrate to entire proximally, long-decurrent with many hyaline, inflated cells, 1-stratose, margins plane or narrowly recurved near base, costa single, strong, commonly dorsally toothed, ending below apex, leaf cells smooth or minutely prorulose by projecting cell ends, cell walls non-pitted or pits not evident, median cells vermicular, 28--45 ´ 5--7 µm. Sexual condition dioicous; archegonial and antheridial plants similar, perigonial and perichaetial buds on stem near branches; perigonial bracts broadly ovate, acute; perichaetial bracts ovate, acute to acuminate. Seta orange to red, smooth, twisted, ca. 1.5 cm. Capsule red, solitary, ovoid, arcuate, cernuous, smooth, not contracted below mouth, 3 ´ 1 mm; annulus none; operculum not seen, reported as long-conic, almost rostrate; peristome hypnaceous, endostome as long as exostome, cilia lacking. Calyptra cucullate, covering 1/2 capsule. Spores 12--24 µm, sometimes germinating inside capsule.
Humus on ground or logs along creeks and rivers, or other moist, shaded habitats; 15--550 m; w B.C.; w Alaska, nw Wash.; Asia.
This is a distinctive species somewhat reminiscent of Climacium because they both have erect secondary stems arising from a creeping primary stem and the plants occur in wet habitats. Pleuroziopsis is lighter green, more slender in appearance with a frondose-dendroid habit, an ovoid, arcuate, cernuous capsule with a hypnaceous peristome, the teeth with fine cross striolations, compared to the coarser dendroid habit of Climacium that has a cylindric, straight, erect capsule with narrow peristome segments that are densely papillose. Another important feature differentiating Pleuroziopsis from Climacium that was not stressed when the family Pleuroziopsidaceae was described is the nature of branching that distinguishes the two genera and the family Climaciaceae. In Pleuroziopsis, the plants are erect from a creeping primary stem, just as they are in Climacium, but they are also frondose-dendroid, i.e., they are flattened and the secondary and tertiary branches are divided, often several times, so the plants are noticeably frondose. In Climacium, on the other hand, the plants are not flattened but the branches arise around the distal end of the erect, secondary stem and the branches seldom, if ever, produce branchlets. The capsules of the two genera are quite different (R. R. Ireland 1968). However, the value at the familial level is not as important since reduced peristomes are known to occur in some families of pleurocarpous mosses, as M. S. Ignatov et al. (1998) have pointed out for the Brachytheciaceae.
Ignatov, M. S., H. Robinson and E. A. Ignatova. 1998. Studies on the exostome of Brachytheciaceae (Musci). Arctoa 7: 153--188.
Norris, D. H. and M. S. Ignatov. 2000. Observations on stem surface anatomy in Climacium and Pleuroziopsis (Climaciaceae: Musci). Arctoa 9: 151--154.