The green links below add additional plants to the comparison table. Blue links lead to other Web sites.
enable glossary links

hoary rock-moss, racomitrium moss, woolly fringemoss

Photo is of parent taxon
Habit Plants forming dark or grayish to yellowish green, yellowish to blackish brown tufts or patches, usually hoary when dry. Plants cladocarpous or rarely acrocarpous.

to 15 cm or more, radiculose at the base or not.

creeping, ascending, to erect, central strand absent.


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 or spreading, straight or curved, sometimes recurved when wet, lanceolate to oblong-lanceolate, less often elliptic, ovate to lingulate, keeled to canaliculate-concave;

margins recurved to revolute, entire or erose-dentate, serrate or cristate at the apex, costa rarely spurred or forked distally, sometimes ending in mid leaf, subpercurrent or excurrent, smooth or papillose, in transverse section reniform to elliptical, sometimes semi-terete or strongly flattened, with (2–)3–15 adaxial cells near base, much larger than abaxial cells, often excurrent as an awn, awn smooth, or toothed or papillose or both;

laminal cells smooth, pseudopapillose, or papillose;

basal cells rectangular to linear, nodulose-porose, usually thick-walled, always with spiral thickenings forming a colored strip along the insertion;

mid leaf cells quadrate to elongate, mostly strongly sinuose-nodulose.


1–3 per perichaetium, brown to reddish brown, 3–7(–10) mm, erect, flexuose.

usually long, straight or rarely slightly arcuate, smooth or papillose, one to several per perichaetium;

vaginula with sinuose-nodulose epidermal cells.

Sexual condition



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.

erect, exserted, symmetric, ovoid, obloid to cylindric, usually smooth or obscurely striate;

stomates present;

annulus present, deciduous;

operculum long-rostrate;

peristome mostly with basal membrane and preperistome, equally thickened and weakly trabeculate both adaxially and abaxially, irregularly split into 2–3 branches to the middle or regularly divided into two filaments nearly to the base.


conic-mitrate, not plicate, often papillose at the apex, covering operculum to 1/2 of capsule.


8–12 µm.


asexual reproduction very rare by gemmae arising from the base of the costa on the abaxial side.

Racomitrium lanuginosum

Grimmiaceae subfam. Racomitrioideae

Habitat Dry, exposed areas, mostly with high light intensity, acidic or seldom calciferous soil and rocks, boulders, cliffs, ledges, scree and in fellfields, polar tundra and tundra-like barrens in mountains, hummocks in peatland and moorland, over raw earth of bog margins
Elevation low to high elevations (0-2300 m) [low to high elevations (0-7500 ft)]
from FNA
AK; CA; ID; ME; MT; NH; OR; WA; AB; BC; MB; NL; NS; NT; NU; ON; QC; YT; Atlantic Islands (Azores, Canary Islands, Falkland Islands, Gough Island, Iceland, Madeira, South Georgia, Tristan da Cunha); Australia; Pacific Islands (Hawaiian Islands, New Zealand); Indian Ocean Islands (Heard Island, Îles Crozet, Îles Kerguelen, Prince Edward Islands, Réunion); Greenland; South Africa; arctic and temperate Asia (including Borneo, Java, New Guinea, Sumatra); Europe; South America (Argentina, Chile, Colombia, Ecuador, Peru); Central America (Costa Rica); Antarctica (Deception Island)
[WildflowerSearch map]

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.)

Genera 4, species ca. 75 (4 genera, 28 species in the flora).

Subfamily Racomitrioideae is characterized by a Racomitrium-type peristome, consistently sinuose-nodulose walls of the laminal cells and epidermal cells of the vaginula, absence of stem central strand, non-plicate calyptrae, and cladocarpous arrangement of the perichaetia. Taxa belonging to this subfamily have sometimes been associated with Ptychomitrium and Campylostelium, and placed in the subfamily Ptychomitrioideae in the Grimmiaceae. Despite their overall morphological similarity, these taxa seem to be only remotely related. In Ptychomitrium the laminal cell walls are straight or weakly sinuose, the calyptrae deeply plicate, and the plants acrocarpous. In addition, the preperistome is absent, and the peristome teeth lack trabeculae and have a characteristic air gap at their base. Moreover, Ptychomitrium is cryptoicous because the male branches are small and arise from the base of vaginula inside the perichaetial leaf circle. The Racomitrioideae consists of four genera that are segregates from the large and heterogeneous Racomitrium in the broad sense.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

1. Laminal cells smooth or pseudopapillose; peristome teeth short, divided to the middle, rarely deeper, into 2-3 irregular prongs.
1. Laminal cells papillose; peristome teeth long, split at least to the middle into 2(-3) filiform, ± regular filaments
→ 2
2. Laminal cells with tall, conical papillae situated over the lumina; alar cells hyaline or yellowish hyaline, thin-walled, forming prominent, decurrent auricles.
2. Laminal cells with large, flat papillae situated over the longitudinal walls; alar cells absent or distinct, brown to yellowish orange, not hyaline, thick-walled
→ 3
3. Hyaline hair-point always present, usually long, strongly papillose eroso-dentate, long decurrent down the leaf margins; seta papillose, sinistrorse when dry; costa percurrent, unbranched; capsule slightly ventricose at base; calyptra smooth or minutely roughened.
3. Hyaline hair-point absent or present, rarely long, smooth to denticulate, never papillose or decurrent; seta smooth, dextrorse when dry (in C. fascicularis and C. corrugatus only once twisted to the left immediately below the capsule and proximally twisted to the left); costa ending well before the apex, often branched and spurred distally; capsule never bulging at base; calyptra distinctly verrucose to papillose.
Source FNA vol. 27, p. 294. FNA vol. 27, p. 266.
Parent taxa Grimmiaceae > subfam. Racomitrioideae > Racomitrium Grimmiaceae
Subordinate taxa
Bucklandiella, Codriophorus, Niphotrichum, Racomitrium
Synonyms Trichostomum lanuginosum
Name authority (Hedwig) Bridel: Muscol. Recent., suppl. 4: 79. (1818) Bednarek-Ochyra & Ochyra: in R. Ochyra et al., Cens. Cat. Polish Mosses, 135. (2003)
Web links