Grimmia reflexidens
Grimmia orbicularis
orb dry rock moss
1–2 cm, central strand absent.
2–5 cm, central strand present.
absent.
ovate to oblong-lanceolate, 0.1–1.15 × 0.3–0.5 mm, keeled, not plicate, margins plane, awns 1–2 mm, very long, smooth to slightly denticulate, flattened basally, long-decurrent, costal transverse section prominent, semi-circular;
basal juxtacostal laminal cells rectangular, sometimes nodulose, thin- to thick-walled;
basal marginal laminal cells rectangular with thickened transverse walls, pellucid in 2–4 rows;
medial laminal cells rounded-quadrate, slightly sinuose, thick-walled;
distal laminal cells yellowish green, 1-stratose with 2-stratose ridges, not bulging, marginal cells 2-stratose, not bulging.
appressed and twisted when dry, erect when moist, broadly lanceolate, abruptly contracted into awn, 2–2.5 × 0.4–0.6 mm, keeled, margins recurved in the middle of the leaf on one or both sides, awns short to long, smooth to denticulate, costa weak proximally, projecting on abaxial side;
basal juxtacostal laminal cells short- to long-rectangular, sinuose-nodulose, thick-walled;
basal marginal laminal cells short- to long-rectangular, straight, with thickened transverse walls;
medial laminal cells subquadrate, sinuose, thick-walled;
distal laminal cells 1-stratose.
arcuate, 2–3 mm.
dioicous, perichaetial leaves enlarged.
autoicous.
absent in northern hemisphere material, emergent to shortly exserted, yellowish brown, oblate, exothecial cells irregularly short-rectangular, thin-walled, stomata absent, annulus of 1 row of quadrate, thick-walled cells, operculum mammillate to rostrate, peristome present, nearly fully-developed, split and perforated only in apex, papillose.]
usually present, exserted, bent down into the cushions by the arcuate setae, yellowish brown to chestnut brown, globose to ovoid, smooth to weakly ribbed, when dry and empty wide-mouthed, exothecial cells thin-walled, annulus present, operculum mammillate, peristome teeth orange, broad, cribrose and irregularly cleft at apex.
cucullate.
Grimmia reflexidens
Grimmia orbicularis
Of conservation concern.
Previous to its discovery in Iceland, as Grimmia grisea (H. C. Greven 1998), G. reflexidens was known from only the Southern Hemisphere. It had previously been collected east of East Bay, Newfoundland, now the only known locality in North America, but was not recognized as G. reflexidens. The latter is similar to G. asperitricha Dixon & Sainsbury of New Zealand, and the two species have been confused by G. O. K. Sainsbury (1945) as well as by R. Ochyra (1993). J. Muñoz (1998b) synonymized G. reflexidens with G. sessitana. However, the former is readily separated from the latter by: (1) enlarged perichaetial leaves, (2) decurrent awns, (3) non-bulging laminal cells, and (4) dioicous sexual condition. Capsules are unknown from Northern Hemisphere material, but G. reflexidens lacks stomata while they are present for G. sessitana. Although G. reflexidens and G. teretinervis both have decurrent awns they are easily separated by a number of characters: G. reflexidens grows in compact cushions, has long awns, and a semicircular costa; G. teretinervis grows in loose clumps, is hyaline-tipped to short-awned, and has a unique costa that is distally almost completely circular in transverse section.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Grimmia orbicularis is a thermophilous species with a preference for sunny, basic substrates. In North America it is known only from scattered localities in the Southwest. It may be confused with G. pulvinata, as both species form comparable hemispherical cushions and usually grow in the same habitat. However, they differ markedly in both gametophytic and sporophytic characters. Grimmia orbicularis has leaves with short- to long-rectangular basal juxtacostal cells with thick and nodulose lateral walls, and 1-stratose margins while G. pulvinata has leaves with quadrate to short-rectangular, thin-walled, basal juxtacostal cells and 2-stratose margins. Grimmia orbicularis has globose to ovoid capsules with broad, orange, cribrose and cleft peristome teeth, and mammillate opercula while G. pulvinata has obovoid capsules with fully developed dark red peristome teeth and rostrate opercula.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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