BFNA Title: Rhodobryum
Author: J. Spence 
Date: February 7, 2005
Edit Level: R Brum+
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden

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XX. RHODOBRYUM (Schimper) Limpricht, Die Laubmoose Deutschlands, Oesterreichs und der Schweiz 2: 444. 1892  * [Greek rhodo, rose, and Bryum, a moss genus]

John Spence

Plants large for the family, dark green or olive-green, sometimes with red tints. Stems secondary to 6 cm, erect, arising from wiry creeping stoloniferous primary stems, unbranched or sometimes innovations arising from below the terminal rosette; rhizoids sparse to abundant, at base of stem or arising as macronemata in leaf axils, micronemata lacking on leafy stems. Leaves small and scale-like proximally, becoming enlarged distally and crowded in a terminal rosette, 4--12 mm, strongly contorted and shrunken when dry, erect-spreading when moist; margins bordered by elongate thickened cells or sometimes border weak or absent, 1-stratose, strongly serrate from mid leaf to apex; distal and median laminal cells hexagonal to rhomboidal, 3--4:1, proximal laminal cells elongate-rectangular, longer than distal cells, alar cells not differentiated; costa typically strong, subpercurrent to more often percurrent to short excurrent as a short and often recurved hairpoint or apiculus, in cross section with 2--4 layers of enlarged guide cells, stereid band small or absent. Specialized asexual reproduction lacking. Sexual condition dioicous; inner perichaetial leaves somewhat differentiated, smaller and narrower than surrounding rosette leaves; inner perigonial leaves small, broad, over-arching enlarged disc-like pale perigonia with abundant paraphyses. Seta 1--8 per perichaetium, red or brown, long-exserted, 2--5 cm, straight to slightly flexuose. Capsule inclined to nutant, brown to red-brown, oblong to cylindric, 3--5 mm, slightly curved and narrowed to mouth, mouth sometimes oblique; operculum low-conic; peristome double, well-developed, exostome teeth lanceolate, acuminate, brown or yellow-brown proximally, hyaline near apex; endostome with high basal membrane, segments lanceolate to subulate, keeled and perforate, cilia 2--4, nodose to appendiculate. Spores 10--22(--25) \um, finely papillose.


Species ca. 25 (2 in the flora): worldwide in temperate to tropical regions, all continents except Antarctica.


Rhodobryum is a genus characterized by relatively large plants with leaves in a distinct rosette (at least in the region of the flora), stoloniferous primary stems, guide cells in two or more layers, and reduced stereid band in the costa.  The chromosomes of Rhodobryum are distinctly different from those of Bryum and Rosulabryum (H. P. Ramsay and J. R. Spence 1996).  Like Roellia and Rosulabryum, more than one sporophyte can mature from the same perichaetium.  Roellia differs from Rhodobryum by its lack of stolons, less contorted shiny pale green leaves that are finely rugose, and much larger laminal cells.  Robust specimens of Rosulabryum andicola and R. canariense differ in their strongly developed stereid band with a single layer of guide cells, smaller leaves, lack of stolons, and presence of rhizoidal tubers and filiform leaf-axis gemmae.  Most species of Rhodobryum occur in the tropics, especially in montane regions.  Recent DNA research suggests that the genus, excepting only Leptostomopsis, is basal to and sister to the remainder of the Bryaceae.


SELECTED REFERENCES  Iwatsuki, Z. and T. Koponen. 1972. On the taxonomy and distribution of Rhodobryum roseum and its related species (Bryophyta). Acta Bot. Fennica 96: 1--22. Koponen, T., X. Li and M. Zang. 1982. A synopsis of Rhodobryum (Musci, Bryaceae) in China. Ann. Bot. Fennici 19: 75--80. Mohamed, M.A. Haji. 1984. A synopsis of the genus Rhodobryum in Asia. J. Hattori Bot. Lab. 55: 281--293. Ramsay, H. P. and J. R. Spence. 1996. Chromosome data on Australasian Bryaceae. J. Hattori Bot. Lab. 80: 251--270.


1. Rosette leaves typically 18--55 in number, leaf margins strongly revolute to mid leaf or well beyond, stereid band relatively well developed, reaching dorsal epidermal cells, without layer of thin-walled cells between.         1. Rhodobryum ontariense


1. Rosette leaves typically 15--21 in number, leaf margins weakly recurved to about mid-leaf, stereid band small, with at least one distinct layer of thin-walled cells before dorsal epidermal cells.     2. Rhodobryum roseum


1. Rhodobryum ontariense (Kindberg) Kindberg, Spec. Eur. N. Amer. Bryin. II: 346. 1897


Plants 1--5 cm tall, mostly unbranched or rarely with slender sub-apical innovations. Stem leaves 4--10 mm, numerous in rosettes, from 18--55, typically more than 20; margins strongly  revolute to above mid leaf, often nearly to apex, apex broadly acute to cuspidate; costa percurrent to short-excurrent into a slender hairpoint in rosette leaves, in cross section with distinct stereid band, reaching dorsal epidermal layer without intervening thin-walled layer of cells; distal and median laminal cells hexagonal, 25--35 × 50--80 \um, (3--4:1), proximal cells longer, to 100 \um, rectangular. Inner perichaetial leaves with costa strong, long-excurrent in denticulate hairpoint. Spores 16--24 µm.


Capsules mature late winter--late fall (Feb.--Nov.). Common on rich soil in forests, along forest edges, on rotten logs, tree bases, soil over rock or rock, often calcareous, sometimes in boggy sites; 0--3000 m, restricted to higher elevations in southern latitudes; Alta, Man., N.B., Nfld., N.S., Ont., Que., Sask.; se Ariz., Ark., Conn., Del., D.C., n Ga., Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Nebr., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Pa., R.I., n S.C., S.Dak., Tenn., w Tex., Vt., Va., W.Va., Wis.; Mexico; Eurasia; Asia (India, Japan, mainland southeast Asia).


This is a common and characteristic species of the eastern deciduous forests, occurring as far south as Arkansas and Georgia, with disjunct populations in the mountains of west Texas, New Mexico and southeastern Arizona.  Rhodobryum ontariense is not found in Arctic tundra and is rare in the northern boreal forests.


2. Rhodobryum roseum (Hedwig) Limpricht, Laubm. Deutschl. 3: 444. 1892


Plants 1--3 cm tall, commonly branched by slender sub-apical innovations. Stem leaves 3--8 mm, relatively few in rosettes, 18--22; margins revolute to about mid leaf or less, apex acute; costa variable, from subpercurrent to percurrent, with slender apiculus, to short-excurrent into a slender hairpoint on median rosette leaves, in cross section with small stereid band, not reaching dorsal epidermal layer because of a layer of intervening thin-walled cells; distal and median laminal cells hexagonal, 25--35 × 50--80 \um, (3--4:1), proximal cells longer, to 100 µm, rectangular. Inner perichaetial leaves with costa variable, from subpercurrent to percurrent or excurrent into a short, smooth to weakly denticulate hairpoint. Spores 16--20 \um.


Capsules mature late summer (Jul.--Sep.). Rare, rich soil, humus and litter in coastal tundra and shrublands or occasionally forests; 0--300 m; B.C.; Alaska; Eurasia; Asia (India, Japan).


This species is found only in coastal and near-coastal regions of Alaska, principally the Aleutian Islands, and adjacent far northwestern British Columbia, and disjunct in the Queen Charlotte Islands.  Sporophytes are rarely produced, and many populations consist of small plants that are sterile or only female. At least some locations of this species are in areas that remained ice-free during the last glaciation.