Bryum
Sp. Musc. Frond., 178, plate 42, figs. 8–12.
plates 43, 44. 1801.
Plants small, gregarious or in dense mats, rarely cushions, white, silver-green, olive, pale green, golden, yellow-green, brown, or yellow-brown. Stems 0.2–1(–2) cm, weakly to strongly rounded julaceous or short-gemmiform, not or weakly branched; rhizoids few or many, micronemata and macronemata absent from stems or present in clusters proximally. Leaves with fertile stem leaves imbricate when dry, erect to erect-spreading when moist, ovate-lanceolate to ovate, concave, 0.2–1(–1.5) mm; base not decurrent; margins recurved proximally, plane distally, or often plane throughout, ± entire, 1-stratose, limbidium absent; apex broadly rounded to acute or rarely acuminate; costa not reaching apex or excurrent, apiculus sometimes present if costa not reaching apex, often hyaline, smooth, guide cells usually absent; alar cells not or somewhat differentiated from juxtacostal cells, usually shorter; laminal areolation distinctly heterogeneous; proximal laminal cells quadrate or short-rectangular, 1–2(–3):1; medial and distal cells short-rhomboidal to elongate-hexagonal or rarely vermicular, (1–)3–6(–8):1, walls thin to incrassate, not pitted. Specialized asexual reproduction by leaf axil bulbils or absent. Sexual condition dioicous; perigonia and perichaetia terminal, leaves same size as vegetative leaves or usually larger, not forming rosette, inner leaves not much differentiated. Seta single, somewhat twisted when dry. Capsule inclined to pendent, ovate or clavate to pyriform, (1–)2–3 mm; hypophysis differentiated or not; operculum weakly convex, short-conic, not rostrate; peristome double; exostome pale yellow or tan, teeth slender lanceolate; endostome separate from exostome or sometimes adherent or absent, basal membrane low to high, segments present, perforate, cilia appendiculate or sometimes absent. Spores shed singly, not as tetrads, 8–15(–18) µm, finely papillose, pale tan or yellow-tan.
Distribution
Nearly worldwide, temperate to arctic-alpine regions, mountains of subtropical or tropical regions.
Discussion
Species 40 (7 in the flora).
Bryum in the strict sense is a genus of small julaceous plants, morphologically similar to Anomobryum. Molecular studies, however, consistently show that the types of the two genera, A. julaceum and B. argenteum, are not closely related. Anomobryum can generally be distinguished from Bryum by its vermicular distal laminal cells and elongate stringlike stems. Bryum species tend to have shorter laminal cells and relatively short, thick, rounded stems. Bryum consists of both silver-white species with hyaline leaf tips, and green to yellow-green species. Many collections of small sterile shoots are difficult to identify. There are at least three undescribed species in the flora area, two of which are discussed under related species. The third is highly distinctive and has been collected recently from southeastern Arizona. Bryum in the broad sense has a reputation for being taxonomically difficult; the genus is highly polyphyletic, and traditionally, many species have been distinguished by minor differences in peristome features. Previous classifications have overemphasized the peristome, placing taxa with strikingly different gametophytes in the same genus. The gametophytes of Bryum vary widely morphologically; this has been used as a basis to reclassify the genus and its relatives (J. R. Spence 2005; Spence and H. P. Ramsay 2005).
Selected References
Lower Taxa
Key
| 1 | Plants silver-green or white; leaves hyaline distally, including apiculus or awn; distal laminal cells elongate-hexagonal (short-hexagonal in B. argenteum var. muticum), less than 16 µm wide | > 2 |
| 1 | Plants yellow-green, golden, olive green, or bright green; leaves not hyaline distally, or apiculus if present sometimes hyaline; distal laminal cells elongate-vermicular to short-rhomboidal, occasionally hexagonal, 6-25 µm wide | > 3 |
| 2 | Plants white-green to silver-green; stems strongly rounded julaceous or sometimes gemmiform; costae not reaching apex, apiculus present or sometimes absent, irregularly incurved when dry; specialized asexual reproduction by leaf axil bulbils. | Bryum argenteum |
| 2 | Plants hoary white; stems evenly foliate, weakly julaceous; costae long-excurrent, awns slender, recurved when dry; specialized asexual reproduction absent. | Bryum lanatum |
| 3 | Distal laminal cells of innovation leaves linear-vermicular to elongate-hexagonal, 6-10 (-12) µm wide; specialized asexual reproduction by leaf axil bulbils; leaf bases red. | Bryum blindii |
| 3 | Distal laminal cells of innovation leaves not vermicular (except B. chryseum), usually 8-12 µm wide or more; specialized asexual reproduction absent; leaf bases red, green, or yellow-green | > 4 |
| 4 | Plants golden yellow to yellow-green, rarely pale green; leaves triangular to ovate; costae long-excurrent, awns slender. | Bryum chryseum |
| 4 | Plants yellow-green, olive green, or bright green; leaves ovate to suborbicular; costae not reaching apex or rarely percurrent, apiculus absent or short | > 5 |
| 5 | Plants green to yellow-green; distal laminal cells of fertile stem leaves elongate- hexagonal, 4-5(-6):1; leaf bases red. | Bryum oblongum |
| 5 | Plants olive green to bright green; distal laminal cells of fertile stem leaves irregularly rhomboidal to hexagonal, 1-4:1; leaf bases green | > 6 |
| 6 | Leaf apices broadly rounded to acute, cucullate; costal apiculus often present, of more than 2 cells; distal laminal cells irregularly rhomboidal, 12-25 µm wide; proximal cells predominantly quadrate. | Bryum calobryoides |
| 6 | Leaf apices acute, not cucullate; costal apiculus absent or of 1 or 2 cells; distal laminal cells hexagonal, 10-16 µm wide; proximal cells short- rectangular. | Bryum veronense |