Rhodobryum (Schimper) Hampe, Linnaea. 38: 663. 1874.
[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, basal membrane high, segments lanceolate to subulate, keeled and perforate, cilia 2--4, nodose to appendiculate. Spores 10--22(--25) µm, 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.
