BFNA Title: Hylocomiaceae
Author: J. R. Rohrer
Date: Dec. 1999
Edit Level: R
Version: 2

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden

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Edit Level R Jan. 30, 2008

 

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XXX. HYLOCOMIACEAE

 

Joseph R. Rohrer

 

Plants medium-sized to robust, forming wefts, often in extensive sheets, growth sympodial or monopodial. Stems prostrate to ascending or erect, often with ascending-arching innovations, irregularly branched to regularly pinnate; paraphyllia sometimes present, branched, cells elongate; pseudoparaphyllia foliose; rhizoids sparse, at base of stems and tips of attenuate branches. Stem leaves often differentiated from branch leaves, very broadly ovate to lanceolate; margins serrate to serrulate, less commonly nearly entire; apex generally acuminate, sometimes acute to rounded; costa typically double, extending 1/4--2/3 leaf length, sometimes single or nearly absent; median cells prosenchymatous, narrowly elliptic to linear-flexuose; alar cells sometimes differentiated. Branch leaves usually smaller, narrower, more sharply toothed, with stronger costa. Sexual condition dioicous. Seta elongate, smooth. Capsule mostly inclined to horizontal; peristome double, exostome commonly reticulate on abaxial surface, but variable, papillose distally; endostome generally with high basal membrane, segments broad, perforate along the keel by narrow slits or broadly elliptic gaps, cilia 1--4. Calyptra cucullate, smooth, naked. Spores spherical, 10--25[--50] \um, finely papillose to nearly smooth.

 

Genera 11, species 26 (7 genera, 12 species in the flora): primarily cool-temperate to subarctic regions worldwide, extending to the tropics in montane habitats.

 

The Hylocomiaceae include some of the largest pleurocarpous mosses of North America. Hylocomium splendens, Pleurozium schreberi, and Rhytidiadelphus triquetrus, which carpet vast areas of forest floor across the northern half of the continent, are among our most common and widespread mosses. The genera of Hylocomiaceae are poor in species but rich in individuals. Many of the North American species are also common across northern Europe and Asia. Because of their robust size, handsome appearance, and abundance, several species in this family are commercially harvested for decorative use in planters. Since its original description, the family has been studied and redefined several times (A. L. Andrews 1954; A. Noguchi 1972; J. R. Rohrer 1985a). Phylogenetic analyses based on ontogenetic, morphological, and anatomical evidence by T.-Y. Chiang (2000) and L. Hedenäs (2004) each suggested that the genera of Hylocomiaceae as defined by J. R. Rohrer (1985b) comprised two or more clades, but the composition of the two main clades differs greatly between the two studies.  Analysis of molecular data has so far been inconclusive (L. Hedenäs 2004). Many of the genera are isolated phenetically, and clearly their cladistic relationships are debatable. The genera of Hylocomiaceae, as defined here, share various combinations of the following derived characters: sympodial growth, branched paraphyllia with elongate cells, differentiated stem and branch leaves, sharply serrate leaf margins, highly variable costa that are often long and double, or single and branched, prosenchymatous prorate leaf cells, reticulate exostome ornamentation, and endostome segments with broadly elliptic perforations.

 

 

SELECTED REFERENCES Andrews, A. L. 1954. Taxonomic notes. XII. The families Rhytidiaceae and Hylocomiaceae. Bryologist 57: 251--261. Noguchi, A. 1972. On the delimitation of the genera of Hylocomiaceae and Rhytidiaceae. J. Hattori Bot. Lab. 35: 155--168. Hedenäs, L. 2004. Morphological and anatomical evidence suggest that ‘Hylocomiaceae’ taxa belong to at least two clades.  J. Bryol. 26: 125--135. Rohrer, J. R. 1985a. A phenetic and phylogenetic analysis of the Hylocomiaceae and Rhytidiaceae. J. Hattori Bot. Lab. 59: 185--240. Rohrer, J. R. 1985b. A generic revision of the Hylocomiaceae. J. Hattori Bot. Lab. 59: 241--278.

 

1. Stems without paraphyllia.

2. Leaf apices rounded to obtuse, often appearing bluntly apiculate because of broadly incurved margins; margins entire except at apex   5. Pleurozium, p. xx.

2. Leaf apices acute to acuminate; margins serrulate throughout.

3. Plants large, at least 2 mm wide measured across leafy stem; stem leaves longer than 2 mm, not or only slightly decurrent; capsules horizontal    4. Rhytidiadelphus, p. xx

3. Plants slender, less than 2 mm wide measured across leafy stem; stem leaves shorter than 2 mm, narrowly decurrent; capsules erect   7. Leptohymenium, p. xx

1. Stems with dense covering of paraphyllia.

4. Plants wider than 4 mm measured across leafy stem, sparsely branched, growth monopodial; stem leaves crowded, falcate-secund, longer than 3.5 mm          6. Rhytidiopsis, p. xx

4. Plants narrower than 4 mm measured across leafy stem, irregularly to pinnately branched, growth typically sympodial; stem leaves not crowded, heteromallous, shorter than 3.5 mm.

5. Stems regularly (1--)2--3-pinnate, usually with yearly innovations forming an ascending series of flat frondose tiers; stem leaves appressed-sheathing on stipe to erect among branches; leaf cells occasionally prorulate          2. Hylocomium, p. xx

5. Stems remotely and irregularly branched to 1--2-pinnate; innovations usually inconspicuous and rarely forming flat frondose tiers; stem leaves erect-spreading to squarrose; leaf cells smooth.

6. Stem leaves broadly cordate-clasping at base, moderately plicate (not obscuring costa); branch leaves with double costa extending less than 1/2 leaf length   3. Loeskeobryum, p. xx

6. Stem leaves not cordate-clasping at base, strongly plicate (often obscuring costa); branch leaves with single, double, or branched costa extending 1/2--3/4 leaf length         1. Hylocomiastrum, xx

 

1. HYLOCOMIASTRUM Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. ed. 2, 11: 486. 1925   *  [Hylocomium, a related genus, and Latin -astrum, incomplete resemblance]

 

Plants prostrate with ascending-arching innovations; growth sympodial. Stems remotely and irregularly pinnate to regularly 1--2-pinnate; paraphyllia dense, highly divided from a multiseriate base into 1--2-seriate branches. Stem leaves often remote, erect-spreading to spreading, broadly ovate, ovate-deltoid, or ovate, strongly plicate, not rugose, not to somewhat decurrent; margins spinose-serrate to serrate in distal two-thirds, serrulate to nearly entire at base; apex acute to acuminate; costa single, double, or rarely triple, sometimes branching, extending 1/3--3/4 leaf length, sometimes ending in a sharp spine; cells smooth; alar cells not differentiated. Branch leaves broadly ovate to ovate-lanceolate, apex acute to acuminate; costa extending 1/2--3/4 leaf length, spinose. Capsule inclined to horizontal; operculum conic; exostome teeth irregularly cross-striolate to somewhat reticulate proximally on exterior surface; endostome segments with narrow perforations along keel.

 

Species 3 (2 in the flora): cool-temperate and boreal regions, North America, Eurasia, n Africa.

 

Proximal leaves of stems and branches of Hylocomiastrum are distinctly shorter than the others and have nearly entire margins, acute to bluntly apiculate apices, and weaker costa. Hylocomiastrum differs from Hylocomium, with which it is often combined, in its shorter-branched paraphyllia, strongly plicate leaves, strong costa that are often single and end in a spine, smooth leaf cells, endostome segments with narrow perforations, and conic-apiculate opercula.

 

 

1. Stem leaves erect, loosely imbricate, ovate to elliptic-ovate, usually longer than 1.7 mm; branch leaves usually longer than 1.2 mm; costa single 1. Hylocomiastrum pyrenaicum

 

1. Stem leaves wide-spreading, distant, broadly ovate to deltoid, usually shorter than 2 mm; branch leaves usually shorter than 1.2 mm; costa usually double in stem leaves, single in branch leaves, but variable      2. Hylocomiastrum umbratum

 

 1. Hylocomiastrum pyrenaicum (Spruce) Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. ed. 2, 11: 487. 1925

 

Hypnum pyrenaicum Spruce, Musci Pyren., no. 4. 1847; Hylocomium pyrenaicum (Spruce) Lindberg

 

Plants soft in appearance, 1--3 mm wide measured across leafy stem, to 12 cm long. Stems irregularly branched to loosely 1-pinnate, not frondose or bushy, innovations inconspicuous; branches turgid. Stem leaves loosely imbricate, becoming more tightly imbricate toward stem tips, erect to erect-spreading, ovate to elliptic-ovate, somewhat concave, 1.5--2.5 x 1.0--1.4 mm; margins serrate distally, serrulate to nearly entire toward base; abruptly narrowed to apex; costa single; median cells 30--60 x 5--7 \um. Branch leaves imbricate, ovate-lanceolate to lanceolate, 1.3--2.0 x 0.4--0.9 mm; costa single. Seta 10--30 mm. Capsule ovoid, 1.3--1.8 mm.

 

Soil, humus, old logs, and rock in moist forests, rarely fens and tundra, often along streams or besides waterfalls, perhaps more common in calcareous areas; 0--3000 m; Greenland; Alta., B.C., N.B., Nfld. and Labr.Nfld., N.W.T., N.S., Ont., Que., Yukon; Alaska, Colo., Maine, Mich., Minn., N.H., N.Y., Vt., Wash., Wis.; Eurasia.

 

2. Hylocomiastrum umbratum (Hedwig) Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. ed. 2, 11: 487. 1925

 

Hypnum umbratum Hedwig, Sp. Musc. Frond. 263. 1801; Hylocomium umbratum (Hedwig) Schimper in P. Bruch, W. P. Schimper & W. T. Gümbel

 

Plants wiry in appearance, 1--2 mm wide measured across leafy stem, to 15 cm long. Stems irregularly to regularly 1--2(--3)-pinnate, often somewhat frondose or bushy from arching innovations; branches slender. Stem leaves distant, erect-spreading to wide-spreading, broadly ovate to deltoid, only slightly concave, 0.8--2(--2.5) x 0.8--1.5 mm; margins spinose-serrate distally, serrulate at base; gradually tapered to apex; costa usually double, sometimes single, single and branched, or triple; median cells 30--65 x 4--7 \um. Branch leaves loosely imbricate, ovate, 0.4--1.2 x 0.3--0.8 mm; costa often single, but variable. Seta 20--45 mm. Capsule ovoid-ellipsoid, 1.5--2.5 mm.

 

Soil, humus, old logs, and rocks in moist forests, especially under spruce-fir; 0--2000 m; B.C., N.B., Nfld. and Labr., N.S., Ont., P.E.I., Que.; Alaska, Maine, Mass., Mich., N.H., N.Y., N.C., Tenn., Vt.; Eurasia.

 

In addition to the numerous highly branched paraphyllia, stems in Hylocomiastrum umbratum (but not H. pyrenaicum) also bear some scattered larger paraphyllia. These are more than twice the size of typical paraphyllia, are lanceolate-subulate with toothed margins, and closely resemble the foliose pseudoparaphyllia. Under a dissecting microscope these larger paraphyllia are clearly visible at 30x magnification scattered among the shorter paraphyllia. In otherwise difficult specimens, the presence of these larger foliose paraphyllia can be used to distinguish H. umbratum from H. pyrenaicum.

 

2. HYLOCOMIUM Schimper in P. Bruch, W. P. Schimper, and W. T. Gümbel, Bryol. Europ. 5: 169. 1852  *  [Greek hylokomos, thick-grown with wood, a deep forest habitat]

 

Plants prostrate to more commonly arching-ascending with annual growth increments forming an ascending series of frondose tiers; growth sympodial, rarely appearing monopodial in reduced Arctic-alpine forms. Stems regularly (1--) 2--3-pinnate; paraphyllia numerous, branched from a multiseriate base into several, long, slender 1--2-seriate strands. Stem leaves somewhat differentiated, tightly appressed on stipe to erect among branches, oblong-ovate to ovate, lightly plicate, sometimes rugose in acumen, not decurrent; margins serrate to serrulate distally, serrulate to nearly entire proximally; apex abruptly narrowed to long, crimpled acumen, occasionally rounded, obtuse, or abruptly acute; costa double, extending 1/4--1/2 leaf length, or sometimes nearly absent; cells occasionally minutely prorate; alar cells not differentiated. Branch leaves smaller, erect-spreading, ovate to elliptic-lanceolate; margins broadly incurved near apex, reflexed at base; apex short acuminate, bluntly acute, or obtuse. Capsule inclined to pendent, mostly bent horizontal at neck; operculum obliquely long-rostrate from conic base; exostome teeth reticulate proximally on exterior surface; endostome segments with broadly elliptic perforations along keel, usually split wide open into one large gaping perforation.

 

Species 1: cool-temperate, boreal, and arctic regions, North America, Eurasia, n Africa, Australia, Pacific Islands (New Zealand).

 

1. Hylocomium splendens (Hedwig) Schimper in P. Bruch, W. P. Schimper, and W. T. Gümbel, Bryol. Eur. 5: 173. 1852

 

Hypnum splendens Hedwig, Sp. Musc. Frond., 262. 1801; Hylocomium alaskanum (Lesquereux & James) Austin; H. proliferum (Bridel) Lindberg; H. splendens var. alaskanum (Lesquereux &. James) Limpricht; H. splendens var. compactum (Lesquereux & James) Macoun & Kindberg; H. splendens ssp. giganteum Vitt; H. splendens var. obtusifolium (Geheeb) Paris

 

Plants 2--3-pinnate with fronds 20--35(--50) mm broad in typical forms (1-pinnate with fronds as narrow as 8 mm in reduced Arctic-alpine forms), 1--3 mm wide measured across leafy stem, to 20 cm long. Stem leaves oblong-ovate to ovate, 1.6--3.2(--4) x 1--1.7 mm; apex abruptly narrowed to a long crinkled acumen in typical forms (in reduced forms, ovate, 1--1.8 x 0.7-1 mm; apex rounded to obtuse or often with an abruptly acute tip); median cells 30--70 x 4--6 \um. Primary branch leaves ovate to elliptic, concave, 0.8--1.3(--2) x 0.3--0.6(--0.9) mm. Branchlet leaves ovate to elliptic-lanceolate, concave, 0.3--0.8 x 0.2--0.4 mm. Seta 5--25 mm. Capsule ovoid to ellipsoid from distinct neck, 1.7--2.8 mm.

 

Carpeting soil, humus, rotten logs, and rocks over extensive areas of forest, especially boreal conifer forest, also common in arctic and alpine tundra; 0--3700 m; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Calif., Colo., Conn., Ga., Idaho, Iowa, Maine, Md., Mass., Mich., Minn., Mont., N.H., N.J., N.Y., N.C., Oreg., Pa., R.I., S.Dak., Tenn., Vt., Va., Wash., W.Va., Wis., Wyo.; Eurasia; Africa; Australia; Pacific Islands (New Zealand).

 

Hylocomium splendens is one of the most common and widespread mosses of the circumboreal forest and Arctic tundra, which covers huge areas of Alaska, Canada, northern Europe, and Siberia. Variation in nutrients and climate produces variation in size, growth pattern, and leaf morphology over this broad range. Plants from coniferous rainforests of the Pacific Northwest are robust, 3-pinnate, and form deep wefts of stair-step innovations. The stem leaves have long, crimped acumens. Plants from the Arctic tundra, however, are much smaller, only once- or twice-pinnate, and usually lack the arching innovations. The stem leaves have obtuse or abruptly acute apices. Although these two forms are quite distinct and could easily be named as separate species, between the temperate rainforest and the Arctic tundra there exist plants of every intermediate form. It is best, therefore, to treat this continuum as a single variable species. It does not seem worthwhile to apply names to the infraspecific variants.

 

 

3. LOESKEOBRYUM Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. ed. 2, 11: 482. 1925  *  For the German bryologist and journalist Leopold Loeske, 1865--1935, and Greek bryon, moss

 

Plants prostrate to ascending-arcuate; growth sympodial [sometimes monopodial]. Stems irregularly branched to regularly 1--2-pinnate; paraphyllia abundant, branched from a 1--2-seriate base into 1-seriate prongs. Stem leaves spreading to squarrose-recurved, ovate to broadly ovate from a broadly cordate clasping base, moderately plicate, sometimes rugose in acumen, not decurrent; margins serrate to serrulate; apex gradually acuminate to abruptly pinched into a slender, slightly channeled acumen; costa double, weak or extending to 1/2 leaf length; cells smooth; alar cells not differentiated. Branch leaves spreading, ovate to elliptic-lanceolate, slightly or not cordate clasping. Capsule inclined to horizontal; operculum stoutly rostrate from conic base; exostome teeth irregularly cross-striolate proximally on exterior surface; endostome segments with broadly elliptic perforations along keel.

 

Species 3 (1 in the flora): temperate regions, e North America, Mexico, West Indies (Dominican Republic), Central America (Guatemala), Eurasia, n Africa.

 

The paraphyllia of Loeskeobryum closely cover the stem and can be inconspicuous at low magnification. They are distinctly smaller than those of Hylocomium, with which Loeskeobryum is often lumped. Morphologically the three species of Loeskeobryum show greater overall similarity to those of Rhytidiadelphus (J. R. Rohrer 1985a).

 

1. Loeskeobryum brevirostre (Bridel) Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. ed. 2, 11: 483. 1925

 

Hypnum rutabulum Hedw. var. brevirostre Bridel, Muscol. Recent. 2(2): 162. 1801; Hylocomium brevirostre (Bridel) Schimper in P. Bruch, W. P. Schimper, and W. T. Gümbel

 

Plants 2--4 mm wide across leafy stems, to 12 cm long. Stem leaves not crowded, slightly concave, (1.1--)2--3 x (1.1--)1.4--1.9 mm; margins often broadly incurved at base of acumen; apex frequently falcate; median cells 30--70 x 5--7 \um; cells of the clasping auricles smaller and rectangular to rhomboidal. Branch leaves concave, 0.8--1.9 x 0.3--1.2 mm; apex acuminate to abruptly acute, straight; costa 1/4--1/2 leaf length. Seta 12--40 mm. Capsule ellipsoid from short neck, 1.6--2.7 mm.

 

Soil, humus, rotten logs, and rocks in moist forests, especially common in the mixed hemlock and cove hardwoods forests of the Appalachian Mountains; 0--2000 m; N.B., Nfld. and Labr. (Nfld.), N.S.; Conn., Ga., Ky., Maine, Md., Mass., N.H., N.J., N.Y., N.C., Ohio, Pa., Tenn., Vt., Va., W.Va.; Mexico; West Indies; Central America (Costa Rica, Guatemala); Europe; n Africa.

 

Reports of Loeskeobryum brevirostre from Ontario and Quebec are suspect. Macoun’s collection from Owen Sound (No. 1191, 28 July 1871, CANM) is correctly identified but far from the Appalachian range of the species. All Quebec collections labeled as L. brevirostre that were examined for this study were misidentified.

 

 

4. RHYTIDIADELPHUS (Limpricht) Warnstorf, Krypt.-Fl. Brandenburg 2: 842, 917. 1906   * [Rhytidium, a moss genus, and Greek adelphus, brother, alluding to a relationship between genera]

 

Hylocomium subg. Rhytidiadelphus Limpricht, Laubm. Deutschl. 3: 590. 1901; Rhytidiastrum Ignatov & Ignatova

 

Plants creeping to ascending or erect; growth monopodial. Stems irregularly and remotely branched to subpinnately branched, rarely with secondary branches; paraphyllia absent. Stem leaves erect-spreading to squarrose, squarrose-recurved, or falcate-secund, broadly ovate or ovate-triangular to ovate-lanceolate, sometimes plicate in proximal half of leaf, sometimes rugose, not or only slightly decurrent; margins serrulate distally, serrulate to nearly entire proximally; apex acuminate; costa double, short or extending to 2/3 leaf length; cells smooth or coarsely prorate; alar cells not differentiated or shorter and wider than basal cells. Branch leaves smaller, ovate to narrowly lanceolate, more abruptly acuminate. Capsule horizontal; operculum conic; exostome teeth cross-striolate to reticulate; endostome segments with broadly elliptic perforations along keel.

 

Species 5 (5 in the flora): cool-temperate and boreal zones, North America, Eurasia, Atlantic Islands, Pacific Islands (New Zealand, Tasmania).

 

M. S. Ignatov and E. A. Ignatova (2003) have described the new genus Rhytidiastrum to include Rhytidiadelphus squarrosus and R. subpinnatus.  Although R. japonicus and R. loreus were not treated in their flora, both taxa would be included in Rhytidiastrum following their key, which differentiates Rhytidiastrum from Rhytidiadelphus on the basis of the costa extending less than half the leaf length versus longer, some leaves with sheathing bases and spreading acumens versus wide-spreading from the insertion, and smooth versus prorate leaf cells.  Rhytidiadelphus triquetrus alone remains in Rhytidiadelphus. On the other hand, ITS and ISSR molecular markers employed by A. Vanderpooten et al. (2003) delineated two pairs of closely related species: R. loreus with R. triquetrus and R. squarrosus with R. subpinnatus.

 

SELECTED REFERENCES Koponen, T. 1971. Rhytidiadelphus japonicus and R. subpinnatus. Hikobia 6: 18-35. Schofield, W. B. and S. S. Talbot. 1991. Rhytidiadelphus japonicus (Reimers) Kop. in North America. J. Hattori Bot. Lab. 69: 265--267.  Vanderpooten, A., L. Hedenäs, and A.-L. Jacquemart.  2003.  Differentiation in DNA fingerprinting and morphology among species of the pleurocarpous moss genus, Rhytidiadelphus (Hylocomiaceae).  Taxon 52: 229--236.

 

1. Leaves plicate; alar cells not or only slightly differentiated from the basal cells.

2. Costa strong, extending at least to midleaf; leaf cells coarsely prorate; stem leaves gradually tapered to a broad, flat (occasionally rugose) acumen    1. Rhytidiadelphus triquetrus

2.Costa weak, extending less than 1/4 leaf length; leaf cells smooth; abruptly narrowed to a slender, channeled, falcate-secund to recurved acumen  2. Rhytidiadelphus loreus

1. Leaves not plicate; alar cells differentiated from the basal cells.

3. Costa extending 1/3--1/2 leaf length; alar cells thick-walled and porose; stem leaves short acuminate         3. Rhytidiadelphus japonicus

3. Costa extending to 1/3 leaf length; alar cells thin-walled and nonporose; stem leaves long-acuminate.

4. Stem leaves not crowded (stem visible between leaves) except at stem tip, erect-spreading to squarrose from nonsheathing broadly ovate-triangular base; plants irregularly branched to pinnately branched, inhabiting moist, usually shaded sites     4. Rhytidiadelphus subpinnatus

4. Stem leaves crowded (stem concealed by leaves), strongly squarrose-recurved from subsheathing ovate base; plants remotely branched to irregularly pinnately branched, inhabiting well-drained, open to partially shaded sites, near the seacoast, or in grassy disturbed habitats          5. Rhytidiadelphus squarrosus

 

1. Rhytidiadelphus triquetrus (Hedwig) Warnstorf, Krypt.-Fl. Brandenburg 2: 920. 1906

 

Hypnum triquetrum Hedwig, Sp. Musc. Frond. 256. 1801; Rhytidiadelphus triquetrus var. beringianus (Cardot & Thériot) Grout

 

Plants robust, coarse and shaggy, 3--8 mm wide measured across leafy stem, to 20 cm long. Stems irregularly branched to unevenly pinnately branched; branches commonly to 25 mm, often arcuate-decurved. Stem leaves wide-spreading, pointing in all directions, crowded at stem tip, ovate-triangular, plicate, rugose, 3.2--4.9 x 1.6--2.5 mm; base cordate-clasping, broadly rounded to the insertion; apex evenly tapered to a broad, flat (occasionally rugose) acumen; costa extending 1/2--2/3 leaf; median cells 30--55 x 5--9 \um, coarsely prorate; alar cells only slightly differentiated from basal cells. Branch leaves ovate to lanceolate, 1.8--3.1 x 0.7--1.6 mm. Capsule oblong-cylindric, 1.8--3.5 mm. 



Soil and humus, less often on logs and rock, in a variety of forests from dry-mesic oak/hickory to wet Thuja swamps, most common in northern coniferous forests; 0--2000 m; Greenland; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Ark., Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Mo., Mont., N.H., N.J., N.Y., N.C., Ohio, Oreg., Pa., R.I., S.Dak., Tenn., Vt., Va., Wash., W.Va., Wis., Wyo.; Eurasia; Pacific Islands (New Zealand).

 

A specimen of Rhytidiadelphus triquetrus from Florida in the Torrey Herbarium (NY) is correctly identified, but the locality is very unlikely.

 

2. Rhytidiadelphus loreus (Hedwig) Warnstorf, Krypt.-Fl. Brandenburg 2: 922. 1906

 

Hypnum loreum Hedwig, Sp. Musc. Frond. 294. 1801

 

Plants robust, soft and sleek, 3--5 mm wide measured across leafy stem, to 15 cm long. Stems remotely and irregularly branched to subpinnately branched; branches commonly to 40 mm, decreasing rather regularly in length distally on the stem. Stem leaves erect-spreading, often falcate-secund or recurved distally, ovate-lanceolate, plicate, not rugose, 3.2--4.2 x 0.9--1.4 mm; base loosely sheathing, not rounded to the insertion; apex rather abruptly narrowed to a long, slender, channeled acumen; costa extending less than 1/4 leaf; median cells 40--80 x 5--7 \um, smooth; alar cells not differentiated from basal cells. Branch leaves narrowly lanceolate, base not sheathing, 1.7--3.6 x 0.4--1.0 mm. Capsule ovoid, 1.3--2.5 mm.

 

Especially common on logs, but also covering soil, humus, rock, and even tree bases, floor of moist coniferous forests, abundant near the coast, but rare elsewhere; 0--1000 m; St. Pierre and Miquelon; B.C., Nfld. and Labr. (Nfld.), N.B., N.S., Que.; Alaska, Calif., Idaho, Mass., Mont., Oreg., Wash.; Europe; Atlantic Islands.

 

A specimen of Rhytidiadelphus loreus from Owen Sound, Ontario (Moxley, July 1925, DUKE) is correctly determined, but the locality is very doubtful. In Quebec R. loreus is known only from Îles de la Madeleine in the Gulf of St. Lawrence.

 

3. Rhytidiadelphus japonicus (Reimers) T. J. Koponen, Hikobia 6: 19. 1971

 

Rhytidiadelphus squarrosus subsp. japonicus Reimers in H. J. O. Reimers and K. Sakurai, Bot. Jahrb. Syst. 64: 559. 1931

 

Plants large, soft, 3--5 mm wide measured across leafy stem, to 7 cm long. Stems remotely and irregularly branched to irregularly 1(--2)-pinnately branched; branches commonly to 15 mm. Stem leaves wide-spreading to squarrose, broadly ovate, not plicate or rugose, 2.1--3.8 x 1.6--3.2 mm; base scarcely sheathing, broadly rounded to the insertion; apex abruptly narrowed to a short, channeled acumen; costa extending 1/3 to 1/2 leaf; median cells 25--55 x 4--7 \um, smooth; alar cells vaguely distinct, golden-orange, slightly wider than basal cells with thickened, porose walls. Branch leaves ovate, 1.5--2.8 x 0.7--2 mm. [Capsule oblong, ca. 2.1 mm.]

 

Under tall forbs in coastal meadows of lower mountain slopes; 0--30 m; Alaska; e Asia. Known from 5 or fewer localities in North America, all in the Aleutian Islands.

 

4. Rhytidiadelphus subpinnatus (Lindberg) T. J. Koponen, Hikobia 6: 19. 1971

 

Hylocomium subpinnatum Lindberg, Hedwigia 6: 41. 1867; Rhytidiadelphus calvescens (Lindberg) Brotherus; R. squarrosus var. calvescens (Lindberg) Warnstorf

 

Plants large, soft, 2--4 mm wide measured across leafy stem, to 15 cm long. Stems irregularly branched to pinnate; branches commonly to 20 mm. Stem leaves not crowded (stem visible between leaves) except at tip, erect-spreading to squarrose, broadly ovate-triangular, not plicate or rugose, 2.3--4.2 x 1.1--2 mm; base not or scarcely sheathing, broadly rounded to the insertion; apex abruptly narrowed to a long, channeled acumen; costa extending to 1/3 leaf; median cells 40--75 x 5--7 \um, smooth; alar cells distinct, shorter and wider than basal cells with thin, nonporose walls. Branch leaves ovate to lanceolate, 1.3--2.8 x 0.4--1.3 mm. Capsule ovoid, 1--2.2 mm.

 

Damp to wet soil, humus, logs, and rocks in swamps and moist forests, often along streams and in spray of waterfalls; 30--2100 m; Alta., B.C., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Yukon; Alaska, Conn., Idaho, Maine, Mass., Mich., Mont., N.H., N.Y., N.C., Oreg., Pa., R.I., Tenn., Vt., Wash., Wis.; Eurasia.

 

For the past several decades, many Canadian and European bryologists have recognized Rhytidiadelphus subpinnatus as a species distinct from R. squarrosus, whereas American bryologists have held to the traditional concept of a broadly circumscribed R. squarrosus that includes R. subpinnatus. T. Koponen (1971) and H. A. Crum and L. E. Anderson (1981) have provided contrasting opinions and worthwhile discussion on the species problem. DNA fingerprinting with ISSR markers showed clear genetic discontinuity between R. squarrosus and R. subpinnatus, supporting specific status for both taxa (A. Vanderpooten et al. 2003). In North America R. subpinnatus is by far the more widespread and abundant taxon. The two taxa are distinct ecologically, but intergrade somewhat morphologically. The most troublesome specimens are those from a few isolated subalpine sites of the Canadian West. The plants grow in wet areas on the forest floor or along the margins of lakes and hot springs in alpine meadows or in open Abies lasicarpa stands. Although their leaf morphology is clearly that of R. subpinnatus, these specimens are less branched and their leaves are more strongly squarrose and crowded. As W. B. Schofield and S. S. Talbot (1991) noted, within one colony plants resembling both taxa can be found.

 

5. Rhytidiadelphus squarrosus (Hedwig) Warnstorf, Krypt.-Fl. Brandenburg 2: 918. 1906

 

Hypnum squarrosum Hedwig, Sp. Musc. Frond. 281. 1801

 

Plants large, soft, 2--4 mm wide measured across leafy stem, to 15 cm long.  Stems remotely branched to irregularly pinnate; branches commonly to 12 mm.  Stem leaves crowded (stem concealed by leaves), strongly squarrose-recurved, ovate, not plicate or rugose, 2.4--4.2 ´ 1.1--1.9 mm; base subsheathing, rounded to the insertion; apex narrowed to a long, channeled acumen; costae extending to 1/3 leaf; median cells 45--80 ´ 5--7 mm, smooth; alar cells distinct, shorter and wider than basal cells with thin, nonporose walls.  Branch leaves ovate to lanceolate, 1.2--2.3 ´ 0.4--0.9 mm.  Capsule ovoid, 1.2--2.2 mm.

 

Usually near seacoast on sand, soil, or rocks, in grassy areas behind beach, in salt marsh, on sea shelf and headlands, or in open thickets and forests; also in grassy disturbed areas, such as lawns, pastures, golf courses; 0--300 m; Greenland; B.C., Nfld. and Labr. (Nfld.); Alaska, Oreg., Wash; Eurasia; Atlantic Islands; Pacific Islands (New Zealand).

 

5. PLEUROZIUM Mitten, J. Linn. Soc., Bot. 12: 537. 1869, name conserved  *  [Greek pleura, side, and ozos, branch, presumably alluding to the pinnate branching]

 

Plants prostrate to erect-ascending; growth monopodial. Stems irregularly to regularly 1(--2)-pinnate; paraphyllia absent. Stem leaves loosely appressed to spreading, distinctly crowded and imbricate at stem tip, ovate to elliptic, wrinkled when dry, but neither plicate nor rugose when wet, shortly decurrent; margins entire except at apex; apex often recurved, rounded to obtuse, often appearing bluntly apiculate because of broadly incurved margins; costa double to nearly absent, extending less than 1/4 leaf length; cells smooth; alar cells relatively few in small, distinct group. Branch leaves smaller, elliptic to lanceolate. Capsule inclined to horizontal; operculum conic; exostome teeth reticulate proximally on exterior surface; endostome segments with elliptic perforations splitting widely along keel.

 

Species 1: cool-temperate to sub-Arctic zones, North America, Mexico, Central America, South America, Eurasia, Atlantic Islands.

 

1. Pleurozium schreberi (Bridel) Mitten, J. Linn. Soc., Bot. 12: 537. 1869

 

Hypnum schreberi Bridel, Muscol. Recent. 2(2): 88. 1801; Calliergon schreberi (Bridel) Mitten; Calliergonella schreberi (Bridel) Grout; Calliergonella schreberi var. tananae (Grout) Grout; Pleurozium schreberi var. tananae (Grout) Wijk & Margadant

 

Plants 1--3 mm wide measured across leafy stem, to 16 cm long. Stems reddish, distinctly seen through wet leaves. Stem leaves moderately concave, 1.5--2.8 x 0.8--1.5 mm; median cells 50--100 x 6--9 \um, obviously shorter at extreme apex; alar cells usually orange-brown, slightly enlarged, quadrate to oblong, 18--40 x 12--28 \um. Branch leaves concave, 0.8--1.9 x 0.3--0.8 mm. Seta 15--43 mm. Capsule ellipsoid, 1.5--2.5 mm. 

 

Soil, humus, and rock, often covering the forest floor in extensive mats, in a variety of forest types from dry oak/pine/aspen to wet spruce muskeg; sometimes in bogs, fens, and grass balds; rarely in tundra; 0--3000 m; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., Alaska, Ark., Colo., Conn., Ga., Idaho, Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Oreg., Pa., R.I., S.Dak., Tenn., Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; Central America; South America; Eurasia; Africa (Algeria, Ethiopia); Atlantic Islands.

 

Pleurozium schreberi is generally a forest dweller and only rarely inhabits Arctic tundra. Arctic specimens often have long, slender, sparsely branched stems. An extreme example is the nomenclatural type of the var. tananae. In addition to the reduced branching and slender stems, its leaves are appressed-imbricate and somewhat smaller than the typical range for the species given in the description above. The distal leaf margins are not much inrolled so the apex appears obtuse to rounded rather than apiculate. I interpret such specimens from Arctic tundra to be rare forms of the species induced by the lower nutrient and harsher climatic conditions present outside of the normal forest habitat.

 

6. RHYTIDIOPSIS Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. 1(3): 1057. 1908  *  [Greek rhytis, wrinkle, and opsis, appearance, having rugose leaves as does Rhytidium]

 

Plants prostrate to ascending and hooked at tips; growth monopodial. Stems irregularly and remotely branched; paraphyllia dense, branched from a 1--2-seriate base into 1-seriate filaments. Stem leaves crowded, erect to spreading, falcate-secund, ovate to lanceolate, strongly plicate, rugose in lower acumen, not decurrent; margins serrulate at apex, otherwise minutely toothed to entire; apex gradually acuminate; costa double, extending 1/4--1/2 leaf length; cells smooth; alar cells ± differentiated. Branch leaves smaller, otherwise similar to stem leaves. Capsule horizontal; operculum conic; exostome teeth irregularly cross-striolate to somewhat reticulate proximally on exterior surface; endostome segments with narrow perforations along keel.

 

Species 1 (1 in the flora): restricted to western North America.

 

1. Rhytidiopsis robusta (Hooker) Brotherus in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. 1(3): 1057. 1908

 

Hypnum robustum Hooker, Musci Exot. 108. 1819

 

Plants robust, (3--)5--8 mm wide measured across leafy stem, to 12 cm long. Stem leaves (2.5--) 3.6--5.3 x 1.2--2.2 mm; median cells 40--90 x 5--9 \um; alar cells shorter and wider than basal cells, 18--38 x 12--25 \um. Branch leaves 2.2--4.0 x 0.9--1.3 mm. Seta 17--30 mm. Capsule ellipsoid when wet, arcutate when dry, 2--3.4 mm.

 

Soil, litter, and rock in montane coniferous forests of the Pacific Northwest, occasionally extending into alpine tundra; 300--2500 m; Alta., B.C.; Alaska, Idaho, Mont., Oreg., Wash.

 

Plants in subalpine forest and alpine tundra are generally smaller with leaves only 2.5--3.5 mm long and leafy stems just 3--4 mm wide.

 

7. LEPTOHYMENIUM  Schwägrichen, Sp. Musc. Frond. Suppl. 3(1)(2): plate 246c. 1828  *  [Greek lepto, thin, and hymen, membrane, alluding to the endostomial basal membrane]

 

Plants prostrate [often with ascending-arching innovations]; growth monopodial or sympodial. Stems irregularly branched to regularly 1--2-pinnate; paraphyllia absent. Stem leaves loosely erect-spreading to squarrose, broadly ovate to ovate-lanceolate, sometimes plicate, not rugose, decurrent; margins serrulate to serrate distally, nearly entire proximally; apex obtuse to acuminate; costa double, extending 1/4--1/2 leaf length; cells smooth or prorulate; alar cells few and small [conspicuously enlarged and lax]. Branch leaves erect to spreading, ovate to elliptic-lanceolate, slightly decurrent; alar cells slightly differentiated. Capsule erect; operculum high-conic or obliquely rostrate; exostome teeth smooth proximally on exterior surface; endostome segments short, narrow, imperforate; cilia absent.

 

Species 3 (1 in the flora): montane in warm-temperate to tropical regions, Southern Appalachians; mountains of Mexico and se Asia.

 

Generic concepts of Leptohymenium have varied greatly, but a constant critical character has been the erect, elongate capsules. The genus is used here in the restricted sense of V. F. Brotherus (1908, 1925) and J. R. Rohrer (1985b) for species that exhibit a sympodial growth form.

 

1. Leptohymenium sharpii (H. A. Crum & L. E. Anderson) W. R. Buck & H. A. Crum, Contr. Univ. Michigan Herb. 17: 64. 1990

 

Pterigynandrum sharpii H. A. Crum & L. E. Anderson, Bryologist 70: 99. 1967; Hylocomium splendens var. tenue  Sharp; Mittenothamnium sharpii (H. A. Crum & L. E. Anderson) W. R. Buck; Taxiphyllum sharpii (H. A. Crum & L. E. Anderson) H. Robinson

 

Plants slender, ca. 1 mm wide measured across leafy stem, to 10 cm long. Stems freely and irregularly branched; sympodial innovations uncommon; branches often elongate and filiform. Stem leaves erect, ovate to oblong-lanceolate, moderately concave, 0.7--1.6 x 0.35--0.7 mm, narrowly decurrent, margin serrulate distally, apex acute to acuminate; cells 30--80 x 4--5 \um, prorulate here and there, shorter and broader at very base, alar cells subquadrate to oblong, 10--17 x 10 \um. Branch leaves concave, 0.3--0.75 x 0.15--0.35 mm. Inflorescences and sporophytes unknown.

 

Wet, shaded rocks in moist montane forests, near waterfalls or in deep ravines; 500--1700 m; N.C., S.C., Tenn.

 

Known from about 10 localities, Leptohymenium sharpii is endemic to the Southern Appalachian Mountains and is apparently rare. Although originally described as a variety of Hylocomium splendens, the stems and branches lack paraphyllia. Over the past thirty years Leptohymenium sharpii has been moved from one genus to another. The occasionally sympodial innovations, decurrent leaves, and prorulate leaf cells suggest that it belongs here. Finding plants with sporophytes would aid greatly in resolving generic placement of this puzzling species.

 

SELECTED REFERENCE  Crum, H. A. and L. E. Anderson. 1967. The status of Hylocomium splendens var. tenue. Bryologist 70: 98--101.

 

 

OTHER REFERENCES

 

Brotherus, V. F. 1908. Musci. In: H. G. A. Engler and K. Prantl, Die natürlichen Pflanzenfamilien, ed. 1. Leipzig.

 

Brotherus, V. F. 1925. Musci. In: H. G. A. Engler and K. Prantl, Die natürlichen Pflanzenfamilien, ed. 2. Leipzig.

 

Chiang, T.-Y. 2000. Phylogeny of the Hylocomiaceae (Mosses, Hypnales) inferred from ontogenetic and morphological characteristics.  Taiwania 45: 66--94.

 

Crum, H. A. and L. E. Anderson. 1981. Mosses of North America. New York.

 

Ignatov, M. S. and E. A. Ignatova. 2003. Moss Flora of the Middle European Russia. Vol. 2: Fontinalaceae--Amblystegiaceae. Moscow. (Arctoa 11, suppl. 2: 609--944.)

 

 

 

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