Racomitrium lanuginosum
Racomitrium
hoary rock-moss, racomitrium moss, woolly fringemoss
racomitrium moss
to 15 cm or more, radiculose at the base or not.
mostly pinnately branched, with many short, lateral branchlets.
crowded, erect-appressed when dry, erectopatent when wet, straight to falcate-secund, linear-lanceolate, 3–5 × 0.6–0.9 mm;
margins recurved to revolute for 1/2–2/3 the leaf length, entire proximally the echlorophyllose part formed by decurrencies from the awn;
apices gradually tapering to a long and slender awn, not decurrent, canaliculate distally, concave to broadly carinate proximally, awn hyaline, densely papillose, broadly and evenly decurrent to 1/4–1/3 along the margins, with decurrencies consistently flat, erosodentate to nearly entire and short, to 30 µm, sharp or blunt teeth, distinctly papillose throughout, spreading at a 40–90º angle;
costa in tranverse-section rectangular to reniform in outline, strongly convex abaxially, 75–100 µm wide basally;
basal laminal cells long-rectangular, 40–90 × 7–8 µm, strongly nodulose, forming a broad orange strip along the insertion;
medial cells becoming long-rectangular to linear, 50–60 × 6–8 µm wide;
distal laminal cells short-rectangular, (10–)15–40 × 7–9 µm.
erect to slightly secund when dry, loosely erect to erect-spreading or spreading-recurved when wet, narrowly ovate- to linear-lanceolate;
margins 1-stratose, recurved to revolute, entire proximally, coarsely dentate along the hyaline border;
apices gradually tapering to a long, slender, hyaline acumen;
awns densely papillose, erose-dentate, long-decurrent, with the decurrencies flat or ruffled;
costa percurrent, in transverse section 2-stratose, becoming 3-stratose in the proximal portion;
laminal cells 1-stratose, sinuose, dull and opaque, distinctly papillose with large, flat papillae covering the longitudinal walls and almost the whole of the lumina except for a narrow central groove;
basal marginal laminal cells long-rectangular, forming 1(–2)-seriate band, consisting of to 30 rectangular, translucent, not sinuose cells;
alar cells not differentiated;
medial cells long-rectangular;
distal cells short-rectangular.
1–3 per perichaetium, brown to reddish brown, 3–7(–10) mm, erect, flexuose.
single or often 2–3 per perichaetium, sinistrorse when dry, strongly papillose.
brown, 1–1.7 mm, smooth, glistening;
peristome teeth (300–)500–700(–900) µm, reddish brown, arising from a low basal membrane, 2-fid almost to the base into filiform, terete, densely spiculate-papillose divisions.
straight, ovoid to ovoid-cylindric, somewhat ventricose in the base;
annulus revoluble, 2–4-seriate;
operculum long-rostrate;
peristome teeth, long, reddish brown, split nearly to the base into 2 filiform, strongly papillose branches.
conic-mitrate to cucullate, naked.
8–12 µm.
spherical, pale yellow, finely roughened.
perichaetial leaves hyaline, oblong, oblong-lanceolate to elliptical, abruptly constricted into a short, smooth or weakly papillose awn.
Racomitrium lanuginosum
Racomitrium
Racomitrium lanuginosum is widely distributed throughout the Nearctic and Greenland, where it reaches the highest possible latitudes, becoming rare and scattered southwards. It usually occupies habitats of varying moisture regimes, but exhibits a tendency for growing in exposed, dry, and insolated situations. The often extensive and tumid patches of it found on rocks and soil are mostly hoary when dry. This is due to the very long hyaline awns that at once separate it from all other species of the broadly conceived Racomitrium. The shape of the hair-points is unique not only in the Grimmiaceae but among the mosses. Niphotrichum species often have a similar hoary appearance due to their long, papillose, hair-pointed leaves, but they differ from R. lanuginosum in having non-decurrent awns and tall, stout, conical papillae distributed over the leaf cell lumina, as well as large and often decurrent hyaline alar cells.
The laminal papillae of Racomitrium lanuginosum are identical to those of the genus Codriophorus, but species of that genus are usually readily distinguished by their muticous leaves. The only exception is C. varius, which often has pilose leaves but the awns are non-decurrent, smooth to faintly denticulate, and never papillose. Moreover, it has long-cylindric capsules, smooth setae, and very long, 1–1.8 mm peristome teeth, but in general sporophytes are produced infrequently in R. lanuginosum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species 3 (1 in the flora).
Traditionally, Racomitrium has been considered as a homogeneous genus characterized by its laminal cells having thick and strongly sinuose to nodulose longitudinal cell walls. This characteristic leaf areolation was typically coupled with a peristome of linear teeth arising from a low or high basal membrane and divided nearly to the base into two filiform, somewhat paired segments that are equally thickened and less prominently trabeculate on both external and internal sides. In addition, the genus was characterized by the consistent lack of a central strand, usual presence of the prostome, sinuose-walled epidermal cells of the vaginula, and cladocarpous sexual condition. This combination of characters made Racomitrium readily recognizable. Revisionary studies of the genus showed that in its traditional circumscription it was an artificial, heterogeneous taxon and, as a result, it has been recently split into four genera, Racomitrium in the narrow sense, Codriophorus, Niphotrichum, and Bucklandiella. Racomitrium in the narrow sense is characterized by: distinctly papillose setae twisted to the left; long, hyaline, strongly papillose awns that are long-decurrent and erose-dentate; large, flat papillae with small secondary papillae densely covering the longitudinal cell walls and almost the whole lumina except for a narrow groove in the middle; peristome teeth divided to the base into 2(–3) filiform branches; and capsules slightly ventricose at the base. The papillosity of the setae is a unique feature of this genus, and is unknown in other acrocarpous mosses. That character, the unusual shape of the awns, and the ventricose capsule make the narrowly conceived Racomitrium readily distinguishable from its segregates.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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