Terry T. McIntosh, Steven G. Newmaster

Mnium sect. Rhizomnium Mitten ex Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. 219[I,3]: 612. 1904

Plants 1-8(-12) cm, in tufts or mats. Stems red or reddish brown, becoming darker, sometimes black when old, usually erect, rarely sinuate at maturity or sterile stems sometimes arching, usually simple, not dendroid; rhizoids brown, macronemata often matted proximally, mainly restricted to stem bases distally, not in longitudinal rows, micronemata present or absent. Leaves green, dark green, or occasionally reddish, reddish brown, or yellow-green, somewhat contorted when dry, erect-spreading and flat, sometimes undulate when moist, obovate, elliptic, or rarely ± orbicular, 1-7(-13) mm; base narrowly short- to long-decurrent; margins plane, green, reddish, or brown, rarely blackish with age, 1-4-stratose, entire; apex usually rounded, occasionally retuse or emarginate, sometimes apiculate; costa ending well below apex (to about 7/8 leaf length and often 2-fid distally), subpercurrent, or percurrent, distal abaxial surface smooth; medial laminal cells elongate, sometimes short-elongate or ± isodiametric, 35-180 µm, sometimes in weakly developed diagonal rows, usually collenchymatous, walls pitted or not; marginal cells differentiated, linear, rhomboidal, or rectangular, in (1-)2-3(-6) rows. Specialized asexual reproduction absent (sometimes by green protonematous rhizoids in R. punctatum). Sexual condition dioicous or synoicous. Seta single, reddish brown, occasionally orange, often pale, 1-5 cm, straight to somewhat flexuose. Capsule horizontal to pendent, yellow or yellowish brown, elliptic, ovate, subglobose, oblong, or cylindric, 1-4.5 mm; operculum conic, conic-apiculate, or conic-rostrate; exostome yellow or brown when mature; endostome yellow or yellowish brown, . Spores 25-50 µm.

Species 13 (8 in the flora): nearly worldwide; mostly Northern Hemisphere.

The presence or absence of micronemata along mature stems is essential when separating species in Rhizomnium (micronemata are smaller, less branched and paler than macronemata, mainly restricted to leaf or branch bases distally). In most instances, micronemata are easy to observe, but growing stems often lack them, particularly in plants of R. magnifolium, so this character should be assessed using older stems, which are sometimes buried in the litter. Occasionally, patches of weakly developed plants of R. gracile have nearly naked stems requiring close inspection of a number of stems in order to observe the micronemata or micronemata initials. Five species of Rhizomnium are circumtemperate or circumboreal, one species is circumarctic, and two are endemic to the flora area.

SELECTED REFERENCE Koponen, T. J. 1973. Rhizomnium (Mniaceae) in North America. Ann. Bot. Fenn. 10: 1-26.

Lower Taxa

• Rhizomnium andrewsianum (Steere) T. J. Koponen
• Rhizomnium appalachianum T. J. Koponen
• Rhizomnium glabrescens (Kindberg) T. J. Koponen
• Rhizomnium gracile T. J. Koponen
• Rhizomnium magnifolium (Horikawa) T. J. Koponen
• Rhizomnium nudum (R. S. Williams) T. J. Koponen
• Rhizomnium pseudopunctatum (Bruch & Schimper) T. J. Koponen
• Rhizomnium punctatum (Hedwig) T. J. Koponen