BFNA Title: Hygrohypnum
Author: D. Jamieson
Date: July 6, 2011
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden
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XX. HYGROHYPNUM Lindberg, Act. Soc. Sc. Fenn. 10: 277. 1872 * [Greek hygros, wet or moist, and Hypnum, alluding to the hygric habitat]

David W. Jamieson


Calliergon subg. Limnobium Kindberg; Calliergon subg. Pseudo-Limnobium Kindberg; Calliergon sect. Molliformia Kindberg; Calliergon sect. Montaniformia Kindberg; Calliergon sect. Ochraceiforme Kindberg; Hygrohypnella Ignatov & Ignatova; Hypnum subg. Limnobium (Bruch, Schimper & Gümbel) Sullivant; Ochyraea Váňa; Pseudohygrohypnum Kanda


Plants small to robust. Stems usually 1--15 cm, irregularly branched, in section cortex of several layers of darkly pigmented, thick-walled cells, rarely with ill- to well-defined hyalodermis with hyalodermis or a layer of cells with a thinner outer tangential wall, central strand well-developed, rarely poorly so, or absent. Leaves ovate to broadly-ovate, oval, orbicular, ovate-to oblong-lanceolate to lanceolate, straight or falcate-secund or both, apex broadly rounded or obtuse to acute, occasionally apiculate from an obtuse or rounded apex, sometimes blunt from an acute apex, usually shallowly to deeply concave, rarely plane; margins entire or weakly denticulate or serrulate, usually plane, sometimes recurved in the apex; costa usually short and double and ending before mid-leaf, occasionally long and double, often single and slender or stout, reaching 1/2--3/4\x leaf length, rarely percurrent; laminal cells medially largely linear-flexuose, sometimes short-rhombic or fusiform, marginally short or very long; alar cells undifferentiated or little differentiated from adjacent cells or variously forming small and irregular to large groups of quadrate, short-rectangular or irregular cells or groups of enlarged and thin-walled to inflated cells, plane or excavated, hyaline, yellow-brown, brown, reddish brown, rarely bright red. Sexual condition autoicous or dioicous; inner perichaetial leaves erect, plane, or nearly so; costa absent, short and double, long and double or single and/or forked; margins plane, rarely recurved, entire or coarsely serrulate, especially at the apex, apex obtusely-acute or long, tapering-acute, medial cells smooth, rarely with a few subapical cells abaxially papillose by distally over-lapping end-walls. Capsule ovoid to oblong-cylindric, erect, symmetrical or inclined, slightly to strongly arcuate; operculum conic or conic-apiculate; peristome double, endostome of 1--3 rudimentary to well-developed cilia.


Species 16 (16 in the flora); widely distributed in the montane, boreal and arctic North Temperate Zone, usually on irrigated rocks or stones in or beside cold, swift mountain streams, occasionally on seepy sites.


The genus Hygrohypnum has long been understood to be taxonomically difficult. As circumscribed here, it remains a repository for a number of coherent and disparate elements. Of late, there are few helpful cladistic and molecular analyses (Ignatov, M. S. et al. 2007; Kanda, H. et al. 2004, 2006; Oliván, G. et al.  2007).  These studies seem to expose just as many uncertainties, if not contradictions, as they give insight. Most troubling, the molecular investigations ignore profound morphological issues.  The genus requires further study.


Difficulties in identification are various. There is variability in leaf shape within a single specimen.  Descriptive terms for leaf shape are imprecisely applied. Failure to remove intact leaves during dissection is problematic. Careful observation of alar cells in intact leaves is absolutely necessary. A pair of sharp, very finely pointed dissecting needles is essential.  Fully formed, mature leaves should be stripped from the stem or branch one at a time, under magnification, to see the leaf insertion and tease the leaf away intact. Alar cells in immature leaves are incompletely developed and shape, wall thickness, wall color, and differentiation are regularly obscured by cytoplasmic contents.  It is strongly recommended that leaves selected for examination be first cleared with a clearing agent such as lacto-phenol or, better, with Hoyer’s solution.


SELECTED REFERENCES: Ignatov, M. S. and E. A. Ignatov. 2004. Moss Flora of the Middle European Russia. Vol. 2. KMK Moscow. Ignatov, M. S. and E. A. Ignatova. 2006. Check-list of mosses of East Europe and North Asia. Arctoa 15: 1--130. Ignatov, M. S., A. A. Gardiner, V. K. Bobrova, I. A. Milyutina, S. Huttenen, and A. V. Troitsky. 2007. On the relationships of mosses of the order Hypnales, with special reference to taxa traditionally classified in the Leskeaceae. In: Newton, A. E. and R. S. Tangney, eds. Pleurocarpous Mosses, Systematics and Evolution, Chapter 9. Systematics Association Special Volume series 71. Oliván, G. Hedenäs, L. and Newton, A. 2007. Phylogeny of Hygrohypnum Lindb. based on molecular data. In: Newton, A. E. and Tangney, eds. Pleurocarpous Mosses, Systematics and Evolution, Chapter 10.  Systematics Association Special Volume series 71.  Kanda, H. 1976. A revision of the family Amblystegiaceae of Japan II. J. Sci. Hiroshima Univ., Ser. B, Div. 2 (Botany) 16: 47--119


1.     Stem section with hyalodermis or at least some cells have a slightly thinner and less pigmented outer tangential cell wall compared with the other epidermal cell walls and the sub-adjacent cortical cells.

2.     Costa uniformly strong and single, percurrent . . .13. Hygrohypnum polare

2.     Costa short and double, or double to mid-leaf, or if single or forking, then ending well before the apex.

3.     Alar cells inflated, forming a distinct group of cells, often becoming red or reddish brown with age; leaf apex acute . . .7.Hygrohypnum eugyrium

3.     Alar cells wider and shorter than adjacent cells, but neither inflated nor abruptly different, marginal alar cells increasing in length distally from the point of insertion, hyaline or yellowish, never red; leaf apex blunt . . .12. Hygrohypnum ochraceum

1.     Stem section with epidermis of small thick-walled cells similar to the sub-adjacent cortical cells.

4.  Leaves falcate-secund or some leaves on the same or different stems within the same specimen falcate-secund or straight.

5.     Leaves exclusively falcate.          

6.     Alar cells undifferentiated from adjacent cells.

7.     Leaf margins finely to coarsely serrulate, especially in apex, narrowly recurved, particularly in the proximal half of leaf . . . .10. Hygrohypnum montanum

7.      Leaf margins always entire and plane . . . . 13. Hygrohypnum styriacum (in part)

6.     Alar cells well differentiated; small, numerous, quadrate to short-rectangular, incrassate or inflated; plane or excavate.

8.     Alar cells inflated . . .7. Hygrohypnum eugyrium

8.     Alar cells small, quadrate to short-rectangular, incrassate.

9.     Leaf apex always acute, margins entire . . . . 8. Hygrohypnum luridum

9.     Some leaf apices obtuse and margins distinctly denticulate, or acute with a few fine teeth . . . .16. Hygrohypnum subeugyrium

5.     Falcate-secund and straight leaves occurring simultaneously on the same stem or on different stems in the same specimen.

10.     Leaf apices always entire.

11.     Leaf apex acute; alar cells numerous, quadrate to short-rectangular; annulus absent . . . .8. Hygrohypnum luridum

11.     Leaf apex abruptly acuminate; alar cells undifferentiated or of a few quadrate cells; annulus present;   . . .15. Hygrohypnum styriacum (in part)

10.     Leaf apices bearing a few fine teeth.

12.     Alar cells inflated, thin-walled, leaf apex always acute; stem epidermis differentiated as an ill-defined hyalodermis . . .7. Hygrohypnum eugyrium

12.     Alar cells quadrate to slightly enlarged, incrassate; some leaf apices obtuse and denticulate; stem epidermis similar to cortical   stem cells . . .16. Hygrohypnum subeugyrium 

4.     Leaves all straight, sometimes secund.

13.     Leaves broadly ovate, oval to orbicular, usually less than 1.5/x as long as wide.

14.     Median marginal leaf cells 60 \um or longer…3. Hygrohypnum bestii

14.     Median marginal leaf cells rarely longer than 55 \um.

15.     Alar cells clearly differentiated, either thin-walled or incrassate.

16.     Alar cells thin-walled, usually hyaline, enlarged, rounded-rectangular, forming a rectangular group whose long axis parallels the leaf margins; leaves mostly broadly ovate to orbicular;  inner perichaetial leaves papillose on the abaxial surface near the apex . . .2. Hygrohypnum alpinum

16.     Alar cells incrassate, clearly pigmented in older leaves, quadrate, short-rectangular or irregular, forming an irregular group; leaves mostly broadly ovate to oval; inner perichaetial leaves smooth abaxially. . .6. Hygrohypnum durisusculum

15.     Alar cells undifferentiated or consisting of a few quadrate to short-rectangular cells, thin-walled or incrassate.

17.    Costa usually single and stout, reaching mid-leaf or slightly beyond, sometimes forked or stout, short and double; plants very coarse and rigid . . .14. Hygrohypnum smithii

17.    Costa almost exclusively short and double, if single, then costa slender and plants soft.

18.     Leaves deeply concave to cochleariform, usually 0.8--1.2 mm, apex obtuse to broadly rounded; inner perichaetial leaf margins entire and recurved; endostomial cilia 2--3 . . .5. Hygrohypnum cochlearifolium

18.     Leaves concave, but never cochleariform, usually 1--1.7 mm, apex tapering to bluntly acute point;  inner perichaetial leaf margins coarsely denticulate and  plane; endostomial cilia rudimentary or wanting . . .9. Hygrohypnum molle

13.     Leaves ovate, to oblong-ovate, ovate-lanceolate to oblong-lanceolate, generally more than 1.5/x as long as wide.

19.     Alar cells clearly differentiated, either inflated and mostly thin-walled or smaller, incrassate and quadrate to short-rectangular.

20.     Leaf apex narrowly recurved along the margin and reflexed as a small apiculus, especially in leaves at or near the stem or branch tips; leaves deeply concave, especially near the apex . . . 1. Hygrohypnum alpestre

20.    Margins of leaf apices plane or variously inrolled, never recurved, apex never forming a reflexed apiculus.

21.     Leaf apices always acute and entire . . .8. Hygrohypnum luridum

21.     Leaf apices acute with a few fine teeth or obtuse and distinctly denticulate . . .16. Hygrohypnum subeugyrium

19.     Alar cells undifferentiated or of a few quadrate to short-rectangular cells not forming a recognizable group.

22.     Leaf apex abruptly acuminate, tapering to a slender tip; bracts surrounding perichaetia and perigonia. . . 15. Hygrohypnum styriacum (in part)

 22.     Leaf apex obtuse or acute, with or without a blunt tip; perichaetia and perigonia not in a bracted complex.

23.     Costa predominantly single to mid-leaf or beyond, sometimes short and double.

24.     Leaf apex obtuse; plants coarse; inner perichaetial leaves plicate, margins recurved. . . 14 Hygrohypnum smithii

24.     Leaf apex acute with a blunt tip; plants coarse, rather Amblystegium-like; inner perichaetial leaves never plicate, margins plane . . . 4. Hygrohypnum closteri

23.     Costa usually short and double, rarely to mid-leaf or  beyond.

25.     Leaf apex entire; leaves usually 0.5-- 0.8 mm . . . 11. Hygrohypnum norvegicum

25.     Margins of the leaf apex uneven to denticulate; leaves usually 1--1.7 mm . . . 9. Hygrohypnum molle



1. Hygrohypnum alpestre (Hedwig) Loeske, Verh. Bot. Ver. Brandenburg 46:198.  1905


Hypnum alpestre Hedwig,  Sp. Musc. Frond., 247, plate 64, figs. 1--4.  1801: Calliergon alpestre (Hedwig) Kindberg; Ochyraea alpestris (Hedwig) Ignatov & Ignatova


Plants usually soft and in easily fragmenting patches, yellow or yellow-green with or without rusty mottling above, older extremities dirty or reddish brown to reddish black. Stems to 9 cm, foliose throughout, often clogged with silt or denuded toward the base; branching irregular; hyalodermis absent; central stand strong.  Leaves usually closely spaced and julaceous, sometimes spreading, generally little changed from wet to dry condition; oblong to oblong-lanceolate, straight, never falcate, (0.9--)1.4--1.6(--1.9) x (0.4--)0.6--0.7(--0.9) mm, deeply concave, almost boat-shaped in the apex, generally tumid julaceous.; apex acute to slightly obtuse becoming reflexed as a squarrose apiculus, though eroded in older leaves; margins entire to uneven in the apex, narrowly recurved especially in the distal 1/3 of the leaf and in the apex; costa long and double with one arm reaching mid-leaf or single to the middle or beyond, or short and double; basal cells becoming shorter, wider, and more incrassate than medial cells; alar cells quadrate, short-rectangular to rectangular in a well-defined group of thick-walled, enlarged, often discolored or excavated cells; medial leaf cells uniformly long-linear-flexuose, (55--)65--90(--105) \um, slightly longer in acute apices; apical and marginal cells generally shorter. Sexual condition  autoicous; inner perichaetial leaves lanceolate to linear-lanceolate, costa absent, slender and single or double to midleaf, plicate, margins entire or sometimes toothed toward the apex. Seta 7--16 mm, reddish brown. Peristome endostome with (2--)3, finely, slightly appendiculate cilia.


Irrigated, emergent acidic rocks in montane and northern streams; moderate elevations, 700--1400 m; Greenland; B.C., Man., Nfld. and Labr. (Nfld.), Nunavut, Ont.; Alaska.; Europe (Russia, Scandinavia).


Hygrohypnum alpestre is most easily recognized by its narrowly recurved, squarrose apiculus, which is best seen in stem and branch tips. Also distinctive is the depth of the leaf concavity, with the leaf tip like that of boat bow.  The same concavity gives the leaves a tumid-julaceous appearance on the stems or branches.  Also, the alar region of quadrate, short-rectangular to rectangular cells is well developed.


2. Hygrohypnum alpinum (Lindberg) Loeske, Hedwigia 43: 194.  1904


Amblystegium molle var. alpinum Lindberg, Musci Scand., 33. 1879


Plants usually soft when wet or dry, pale yellow, brownish yellow-green or bright green.  Stems to 5 cm, leafy throughout, branching irregular, ascending to erect; hyalodermis absent; central strand hyaline to brownish. Leaves appressed-imbricate and plane or erect-spreading and convoluted-ruffled parallel to the long axis of the leaf, broadly ovate to usually oval or orbicular, (1--)1.2--1.6(--1.8) x (0.9--)1--1.7(--1.8) mm; apex broadly acute to shortly apiculate, apiculus sometimes folded; margins entire, less often finely denticulate or serrulate in the apex; costa slender, usually short and double, sometimes single and forked; basal cells shorter, longer or little changed from medial cells, usually thicker walled, hyaline, alar cells enlarged to slightly inflated, irregular to rectangular, often excavated, forming a more or less rectangular group, the long axis of which is parallel to the alar margin, medial cells short-fusiform to linear-flexuose, 35--60(--64) x (4--)5--6 \um, marginal cells little changed from medial cells, apical cells shorter. Sexual condition autoicous; inner perichaetial leaves linear-lanceolate to linear, costa absent or faintly single or double, 0--4 deep plicae, apical leaf margins coarsely serrate, apices with a few abaxial cells coarsely papillose by distally over-riding end walls. Seta 8--20 mm, yellow-red, orange-red to red; Peristome endostomial cilia rudimentary or absent.


Irrigated  emergent, acidic rocks in montane streams; low to moderate elevations, 200--850 m ; B.C.; Alaska, Calif., Idaho, Montana, Washington; Europe.


Hygrohypnum alpinum is disjunct from Europe to western North America. Its broadly ovate to regularly orbicular leaves coupled with the rectangular group of thin-walled, enlarged, irregular to rectangular alar cells make the species distinctive.  The convoluted ruffling of the leaves and the abaxial papillae of the inner perichaetial leaves are additional distinguishing traits.


3. Hygrohypnum bestii (Renauld & Bryhn) Holzinger,  Bryologist 4: 12, plate 22. 1901


Hypnum molle ssp. bestii  Renauld & Bryhn,  Bull. Acad. Int. Geog. Bot. 10: 7. 1901; Hygrohpnum bestii (Renauld & Bryhn) Brotherus: H. molle var. bestii (Renauld & Bryhn) Habeeb; Hygrohypnella bestii (Renauld & Bryhn) Ignatov & Ignatova; Limnobium bestii (Renauld & Bryhn) Holzinger


Plants coarse and stiff, rarely soft, olive-green, often yellow or dull, yellowish green with golden mottling, regularly silty. Stems to 12 cm, often denuded from the base or bearing persistent, shredded leaf bases, rarely foliose throughout; branching irregular; hyalodermis absent; central stand weak or absent. Leaves somewhat distant, weakly appressed-imbricate or erect when wet, variously contorted when dry, ovate to broadly-ovate, (1--)1.5--2.5(--3) x 1--1.5(--2) mm; apex obtuse, or somewhat acute; margins entire or uneven apically, rarely denticulate, plane to broadly and shallowly concave, strongly decurrent or scarcely so; leaf bases strongly adherent and persistent by the incrassate basal cells and cortical stem cells; costa usually strong and double from a massive base with one or both branches reaching mid-leaf or very strong and single reaching beyond mid-leaf, often bearing 1--3 forks, yellow-green, becoming brownish in age; basal cells usually strongly incrassate and yellowish, turning yellow-brown in age, the pigmentation often creating a radiating sunburst effect at and around the base of the costa; alar cells undifferentiated, or forming an imprecisely defined group of quadrate, short-rectangular or irregular cells; median leaf cells linear-flexuose to broadly rhombic-flexuose, (40--)60--120(--170) \um, areolation homogeneous or irregularly interspersed with very wide cells;  apical cells usually rounded-quadrate to rhombic; marginal cells from the proximal 1/3 to the distal 1/4 of the leaf very long, 60--250 \um. Sexual condition dioicous; inner perichaetial leaves linear-lanceolate, costa absent, single to midleaf or short and double, multi-stratose through the mid-line of the leaf, lamina 2-stratose. Seta 12--25 mm, red to dark, maroon-red. Peristome endostome with 1--3 weakly appendiculate cilia.


Irrigated, often silt covered rocks in montane streams; moderate to high elevations, 1500--3000 m; Alta., B.C., N.B., N.S., Ont., Que.; Alaska, Calif., Colo., Idaho, Michigan, Montana, N.Mex., Oreg., S.Dak., Utah, Wyo.; Asia (Russia in Kamchatka).


Much confused in North America with H. molle and H. duriusculum, H. bestii is readily distinguished by its diagnostically long marginal leaf cells, to 90 \um or longer.  Long considered a western North American endemic, it is now known to have remarkable outliers at the Lakehead on Lake Superior, the Distal Peninsula of Michigan, Quebec’s Gaspé Peninsula, New Brunswick, and Nova Scotia’s Cape Breton Highlands. It has recently been reported, and not unexpectedly so, from Kamchatka in the Russian far-east.


4. Hygrohypnum closteri (Austin) Grout, Bryologist 13: 14. 1910


Hypnum closteri Austin, Musci Appalachiani, 439. 1870; Amblystegium holzingeri Renauld & Cardot; Hypnum malacocladum Cardot & Thériot


Plants soft and spindly, dull, dirty green. Stems to 15 cm, prostrate to somewhat ascending, frequently denuded at the base, branching irregular; hyalodermis absent; central strand well-developed.  Leaves distant, uniformly straight, loosely patent when wet, becoming somewhat erect spreading, markedly shrunken and twisted upon drying; narrowly ovate, ovate-lanceolate to lanceolate, (0.3--)0.6--0.9(--1.75) X (0.2--)0.3--0.4(--0.75) mm, plane or rarely weakly concave, margins entire, apex acute; costa usually single reaching 1/2--1/3\x leaf length, much less frequently short an double or single and forked; basal cells variable, little changed from medial cells or shorter, longer and wider, alar cells usually little different from adjacent basal cells or as a few gradually widened quadrate or short-rectangular cells, medial cells fusiform or rhombic, straight or flexuose, sometimes linear-flexuose, (23--)30--50(--63) X (4--)6--7(--13) \um, marginal and apical cells shorter,. Sexual condition autoicous, perigonia and perichaetia occurring individually or in 1- or 2-sexual pairs; inner perichaetial leaves triangular-lanceolate, erect, 1.5--2 mm, plane, not plicate, costa single, cells smooth. Seta 7--10 mm, yellowish or yellowish red, Peristomial endostome with 1--3 cilia.


Irrigated or submerged rocks in streams; Low to moderate elevations, 20--1500; D.C., Maine, N.C., N.Y., Pa., Vt.


Hygrohypnum closteri is an enigmatic little plant that is so unlike the main body of Hygrohypnum that it is surely ill-placed in the genus.  Indeed, the author and others have noted its Amblytegium-like appearance.  Perhaps molecular tools can resolve the issue. Sadly, its habitat along the eastern seaboard of the flora region may be destroyed. 


5. Hygrohypnum cochlearifolium (Venturi in DeNotaris) Brotherus,  Naturl. Pflanzenf. 1(3): 1039.  1909

Limnobium cochlearifolium Venturi in De Notaris, Erbar. Critt. Ital., ser 2, fasc. 10, n. 453. 1871; Hypnum goulardii Schimper; Calliergon goulardii (Schimper) Kindberg; Hygrohypnum  smithii var. goulardii (Schimper) Wijk & Margadant; Ochyraea cochlearifolia (Venturi in DeNotaris) Ignatova & Ignatova

Plants very soft, forming loosely woven, easily fragmenting, often silt-clogged patches or small, tightly woven patches, usually yellow to yellow-green with conspicuous rusty mottling.  Stems to 5 cm, usually shorter, usually un-branched, or infrequently and irregularly so; hyalodermis absent; central strand weak and poorly differentiated. Leaves crowded or very distant, when wet loosely imbricate or spreading, upon drying either changing little or shrinking visibly, usually ovate to very broadly ovate or ovate-elliptic, (0.5--)0.8--1.2(--1.5) x (0.3--)0.6--1(--1.3) mm ; apex usually obtuse or rounded, rarely acute, regularly cucullate; margins entire, recurved in small leaves, or mostly plane in larger leaves; concavity conspicuous, very deep to cochleariform; costa usually short and double with one arm reaching mid-leaf, sometimes short and single to mid-leaf or absent; basal cells variable; alar cells thin-walled, undifferentiated, or with a few quadrate, short-rectangular or irregular cells, never forming a clearly, defined group; medial leaf cells short fusiform, short  linear-flexuose or rhombic, 26--48(--55) x (4--)5--6(--8) \um; apical cells shorter to more rhombic; marginal cells shorter. Sexual condition poorly understood; perigonia not seen; perichaetia too few to generalize. Seta 12--16 mm, yellowish to reddish brown. Peristome endostome with 2--3 cilia.

Acidic rocks in irrigated streams or on shaded, irrigated cliffs and boulders; moderate to very high elevations,1300--3700 m; Nunavut; Yukon; Alaska, Colo., Montana; Europe. 

Hygrohypnum cochlearifolium is rare in the flora region and is documented by eight examined specimens.  These specimens come from the far north or as disjunctions south along the Rocky Mountains to Colorado.  It may be recognized by the following character combination; leaves tiny, usually less than 1 mm; leaves vary from ovate to broadly ovate to ovate-elliptic with generally recurved margins; costa usually short and double; and alar cells are essentially undifferentiated.  Most distinctive is the leaf concavity.  No other species in the genus has leaves so deeply concave.


6. Hygrohypnum duriusculum  (De Notaris) D. W. Jamieson, Taxon 29: 152. 1980


Limnobium duriusculum  De Notaris, Erb. Crittog. Ital., 204. 1869; Calliergon circulifolium (Müll. Hal. & Kindberg in Macoun) Kindberg; C. dilatatum (Wilson in Schimper) Kindberg; C. pseudo-arcticum (Kindberg) Kindberg; Hygrohypnella duriuscula (DeNotaris) Ignatov & Ignatova; Hygrohypnum dilatatum (Wilson) Loeske; H. eugyrium var. dilatatum (Wilson in Schimper) Grout; Hypnum circulifolium Müll. Hal.. & Kindberg in Macoun; H. dilatatum Wilson in Schimper; H. pseudoarcticum Kindberg; Limnobium pseudoarcticum (Kindberg) Kindberg; Ochyraea duriuscula (DeNotaris) Ignatov & Ignatova


Plants usually coarse and stiff, bright yellow-green, dull olive-green, dirty yellow or yellow-brown, all with or without rusty mottling.  Stems to 7 cm, foliose throughout or commonly denuded from the base; branching irregular and usually ascending; hyalodermis absent; central strand strong.  Leaf appearance varies within and between the wet and dry conditions, wet leaves appressed-imbricate and sometimes secund or spreading and somewhat contorted, upon drying all leaves exhibit varying degrees of shrinkage, spreading or contortion, contortion may involve twisting to the left and toward the stem or inrolling of the margins toward the costa with concomitant twisting, very broadly-ovate, oval to orbicular, less often ovate, plane or shallowly concave, (0.8--)1.1--1.7(--2.2) x (0.6--)0.8--1.3(--1.7) mm; apex acute, obtuse or shortly apiculate; margins usually entire, rarely denticulate, plane or narrowly recurved at the alar margin; leaf base often narrowly decurrent and sometimes clasping the stem; costa short and double with arms often reaching mid-leaf, sometimes single and forked reaching to beyond mid-leaf; basal cells wider, longer, thicker-walled and often more discolored than medial cells, alar cells in a well-defined group of quadrate, short-rectangular or irregular, incrassate, usually discolored, plane or often excavated cells; median leaf cells short to long-fusiform or linear-flexuose, (26--)30--70(--90) x (3--)5--7(--9) \um.; apical and marginal cells shorter. Sexual condition autoicous, inner perichaetial leaves with apical, abaxial laminal cells smooth. Seta 9--24 mm. yellowish red, red or maroon.  Peristome endostome usually with 1--3 well-developed cilia.

Irrigated, emergent acidic rocks in montane streams; low to very high elevations, 200--3600 m; Greenland; Alta., B.C., Nfld. and Labr. (Nfld.), N.S., Ont., Que.; Alaska, Ariz., Calif., Colo., Conn., Idaho, Mass., Maine, Mont., N.C., N.H., N.Mex., Nev., N.Y., Tenn., Utah, Vt., Va., Wash., Wyo.; Europe; Asia.

Hygrohypnum duriusculum is at the center of a much confused group of species.  Included are H. duriusculum, H. molle, H. alpinum and H. bestii. These species may be distinguished as follows:  Hygrohypnum duriusculum exhibits very broadly ovate to oblong-elliptical, oval to orbicular leaves, alar cells forming a well-defined broad group of quadrate, short-rectangular or irregular often excavated cells with thickened, regularly discolored walls.  Hygrohypnum molle occurs only in western area of the flora, leaves mostly ovate to broadly-ovate with an acute, but blunt apex; alar cells essentially undifferentiated from surrounding cells; moreover, leaves little changed from wet to dry condition and more or less straight and loosely imbricate.  Hygrohypnum alpinum is also a western species; leaves typically orbicular with alar cells forming rectangular group of more or less rectangular or irregular, enlarged, thin-walled cells.  Hygrohypnum bestii stands alone in having exceedingly long marginal laminal cells, generally exceeding 60 \um.  It should be noted that while H. duriusculum occurs across the continent the plants from western North America are somewhat smaller than those from the east.


7. Hygrohypnum eugyrium (Schimper) Loeske, Verh. Bot. Ver. Brandenburg 46:198. 1905


Limnobium eugyrium Schimper, Bryol. Eur. 6: 73, plate 579. 1855; Calliergon eugyrium (Schimper) Kindberg; Hygrohypnum eugyrium var. mackayi (Schimper) Brotherus; Pseudohygrohypnum eugyrium (Schimper) Kanda


Plants yellow-green, pale green, bright green, often exhibiting a golden-brown to deep metallic red mottling, most plants exhibiting a striking satin-like lustre or sheen, infrequently becoming dark red, reddish brown or brown in age. Stems to 6 cm, mostly shorter, prostrate or ascending, branching irregular; hyalodermis poorly developed as an epidermal layer with outer tangential wall slightly thinner walled; central strand present.  Leaves changing little from wet to dry, variously loosely appressed or imbricate or loosely spreading, ovate, oblong-lanceolate to lanceolate, rarely broadly-ovate or broadly oblong-lanceolate, straight or falcate, generally quite concave, (0.9--)1.1--1.8(--2) x (0.3--)0.5--0.8(--1.2) mm, leaf base clasping the stem, margins entire or with a few small teeth in the apex, plane or folded along one side as a wing or in-rolled from both margins in the distal half to become somewhat tubulose, apex acute or gradually to abruptly long tapering, margins inrolled just below the apex may give the appearance of an apiculus; costa mostly short and double and slender, frequently with one or both arms reaching mid-leaf, rarely single to mid-leaf or beyond; basal cells shorter or longer and wider than medial cells, incrassate pitted and discolored, alar region of 6--12 enlarged or inflated, usually excavated quadrate to rectangular cells in a clearly defined group, cell walls hyaline or dark red or reddish brown in age, marginal alar cells always thin-walled while inner alar cells are regularly incrassate and occasionally pitted, pigmentation occluding the lumina in age, medial cells fusiform-flexuose or linear-flexuose, 45--75 x 4--5 \um,.  Sexual condition autoicous; inner perichaetial leaves erect, long, linear-lanceolate, tapering to an acute to acuminate apex, entire or coarsely serrulate in the apex, costa variable, 2--4 plicae, cells smooth. Seta 13--16 mm, yellow-brown to red. Peristome endostome with 2--3 cilia.


Irrigated acidic rocks in or along montane streams; low to moderate elevations, 150--750 m; N.B., Nfld. and Labr. (Nfld.), N.S., Que.; Conn., Ga., Maine, Md., N.C., N.H., N.Y., Ohio, Pa., Tenn., Vt., Va., W.Va.; Europe; Asia (Japan).


Falcate leaved forms of Hygrohypnum eugyrium may be confused with H. luridum and H. ochraceum.  Hygrohypnum eugyrium is set apart, most conspicuously, by quadrate to rectangular alar cells conspicuously inflated and regularly excavated and in age becoming a conspicuously red to reddish brown color, which often occludes cell lumens.  In addition, the hyalodermis is much weaker and less conspicuous than that of H. ochraceum, and under a hand-lens or dissecting scope the abaxial leaf surface exhibits a satin-like sheen.


8. Hygrohypnum luridum (Hedwig) Jennings, Man. Moss. West. Pennsyl., 287. 1913


Hypnum luridum Hedwig, Spec. Musc. Fond., 291. 1801; Calliergon pseudomontanum (Kindberg) Kindberg; Hygrohypnum palustre (Hedwig) Loeske; H. palustre var julaceum (Schleich. ex B.S.G.) Loeske; H. palustre var. subsphaericarpon (Schleicher ex Bridel) Loeske; H. pseudomontanum (Kindberg in Macoun) Grout; Hypnum columbicopalustre Müll. Hal. & Kindberg in Macoun; H. palustre Hudson ex Bridel; H. pseudomontanum Kindberg in Macoun; H. subeugyrium var. occidentale Cardot & Thériot; Limnobium pseudomontanum (Kindberg) Kindberg; Scleropodium krausei (Müll. Hal.) Macoun & Kindberg in Macoun


Plants slender to robust, yellow-green to yellow-green with rusty mottling, less often yellow-brown, bright-green, blackish green, regularly grading from one color to another within the same plant. Stems to 6 cm, mostly prostrate but ascending at the tip, usually foliose throughout; branching irregular; hyalodermis absent; central strand well-developed.  Leaves variable, but changing little from wet to dry, lanceolate, often oblong-lanceolate, ovate and occasionally broadly-ovate, (0.5--)1--1.5(--2.5) x (0.25--)0.4--0.75(--1.1) mm, straight or falcate, rarely almost circinate, mostly imbricate, often julaceous; apex acute or slightly short apiculate, margins entire, regularly inrolled; costa single and short to percurrent or short and double or absent, often all within the same plant; basal cells wider and shorter than medial cells, medial cells short-rhombic to linear-flexuose, (28--)30--55(--95) x (4--)5--7(--12) \um; alar area usually present as a well-defined group of quadrate to short-rectangular or irregularly shaped cells, thin and hyaline or incrassate and discolored yellow-brown or reddish brown, plane or excavated and when excavated cells may be inflated, marginal and apical cells shorter;. Sexual condition autoicous, inner perichaetial leaves lanceolate, costa single, short and double or absent, cells smooth. Seta 8--24 mm, capsule exannulate. Peristome endostome with 1--3 poorly to well-developed cilia.


Irrigated calcareous rocks, stones or wood or irrigated with calcareous water in montane streams; moderate to very high elevations, 450--3200 m; Alta., B.C., Man., N.B., Nfld., Nunavut, N.W.T., Ont., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Mich., Minn., N.H., N.J., N.Mex., N.Y., Ohio, Utah, Vt., Wash., W.Va., Wyo.; Europe; Asia.


Hygrohypnum luridum is a highly variable species for which numerous subspecific taxa have been recognized; there are, however, no reliable distinguishing features among the supposed subspecific taxa.  In North America three forms are regularly seen, to which no taxonomic recognition is given.  Two have falcate leaves and differ essentially in size, one large and one small.  A third form has leaves that are essentially straight and vary in stance from imbricate to julaceous. Complicating this is the fact that the small, falcate-leaved forms intergrade with those having straight leaves and may occur as alternating regions on the same stem. In all cases, however, the costa varies from short and double to either short or long and single and is coupled with a well-defined group of quadrate, short-rectangular or irregularly shaped alar cells. In large, falcate-leaved forms in the West, the single costa is often strong and single to almost percurrent.  Hygrohypnum luridum is the only calcicole in the genus. It occurs on calcareous rock or on other substrates irrigated with calcareous water.


9.Hygrohypnum molle (Hedwig) Loeske. Moosfl. Harz., 320. 1903


Hypnum molle Hedwig. Spec. Musc. Frond., 73, plate 70, fig.  7--10. 1801; Calliergon molle (Hedwig) Kindberg;  C. submolle (Kindberg) Kindberg; Limnobium submolle Kindberg; Ochyraea mollis (Hedwig) Ignatov


Plants soft, yellowish green or olive-green. Stem to 10 cm, procumbent, usually leafy throughout, branching irregular, widely spaced, often attaining the length of the stem; hyalodermis absent; central strand present. Leaves closely to distantly spaced, loosely imbricate and straight, young branch leaves slightly twisted at the apex when dry, otherwise leaves little different wet or dry, broadly ovate, rarely ovate to almost orbicular, (0.8--)1--1.75(--2) x (0.6--)0.75--1.2(--1.25) mm; apex tapering gradually to an acute, but blunt tip; margins entire, undulating or finely denticulate in the distal half, especially in the apex; concavity shallow to deep; costa usually short and double, with slender arms, the longer reaching mid-leaf, or just beyond; basal cells longer, shorter, and slightly more incrassate than medial cells with few pits or none and discolored or not,  alar cells undifferentiated or of a few quadrate, short-rectangular or irregular cells, scarcely different from surrounding cells; medial leaf cells rhomboid to linear-flexuose, (24--)32--52(--74) x (3--)5--6(--8) \um; apical cells little different; marginal leaf cells 30--60 \um, rarely reaching 60 \um. Sexual condition autoicous; inner perichaetial leaves with some apical cells abaxially papillose by apically over-riding end walls.  Seta 6--15 mm, orangish red, reddish brown to deep maroon. Peristome endostomial cilia rudimentary or wanting.


Irrigated or seepy acidic rocks in or along montane streams; moderate to very high elevations, 650--3300 m; B.C.; Alaska, Calif., Colo., Oreg., Wash.; Europe.


 Hygrohypnum molle has been much confused with H. duriusculum and H. bestii and less so with H. alpinum.  The essential features of H. molle are the undifferentiated alar cells of the broadly ovate, distinctly concave leaves, which taper to an acute, but blunt, slightly denticulate apex.  In addition, the leaves are essentially straight and loosely imbricate, little differing wet or dry.  Comparisons with H. alpinum, H. duriusculum and H. alpinum can be found in the discussion of H. alpinum.


10. Hygrohypnum montanum (Lindberg) Brotherus, Naturl. Pflanzenf. 1(3):1039. 1909


Amblystegium montanum Lindberg, Musci Scand., 33. 1879; Calliergon montanum (Lindb.) Kindberg; Hygrohypnum eumontanum H. A. Crum, Steere & L. E. Anderson;  Limnobium montanum (Lindberg) Kindberg; Ochyraea montana (Lindberg) Ignatov & Ignatova


Plants bright or dull-green, yellow or yellow-green, dark brown, in general only the youngest parts are yellow to yellow-green. Stems to 2 cm, generally less, prostrate to slightly ascending at the tips, branching irregular, hyalodermis absent, central strand absent. Leaves little different wet or dry, variously straight or falcate and squarrose-canaliculate in the distal half, upon drying shrinking laterally with a slight in-rolling of the margins with a concomitant twisting in the leaf tip, usually ovate, sometimes ovate-lanceolate, but may be broader or narrower, (0.3--)0.5--0.9(--1.1) x (0.25--)0.3--0.5(--0.9) mm, broadly concave in the proximal half, apex acute to somewhat acuminate, margins narrowly recurved in the proximal half, or less often plane, coarsely to finely serrulate, most conspicuously in the distal half or entire; costa slender, usually short and double; basal cells changing little from medial cells or becoming wider, in either case becoming more incrassate and irregularly pitted, alar cells undifferentiated or forming a scarcely differentiated group of quadrate to short-rectangular or irregular, incrassate, slightly pitted yellowish cells, medial cells short-fusiform to long, linear-flexuose, (17--)25--50(--69) x (3--)4--5(--6) \um, cells toward the  apex little different, although a few cells may be papillose by means of anteriorly over-riding end-walls.  Sexual condition autiocous; inner perichaetial leaves lanceolate with a long tapering apex, costa variable, single and slender or broad and forking, coarsely serrulate in the apex, cells smooth,. Seta 10--17 mm, yellowish red to red. Peristome endostome of 2--3 cilia.


Irrigated, sand covered rocks in or beside montane streams; moderate elevations, 500--700 m; N.B., N.S., Que.; Mass., N.H., N.Y., Vt.; Europe (Scandinavia).


Hygrohypnum montanum is most easily recognized by a combination of individually variable features; tiny leaves ovate to ovate lanceolate in shape, recurved proximal leaf margin, serrulation of the distal leaf margins, and absence of a central strand.  Also useful, but difficult to see are the few abaxial apical cells that are papillose by anteriorly over-lapping end-walls. It is a puzzling little plant reminiscent of Campylium. Perhaps molecular work might illuminate that point.


11. Hygrohypnum norvegicum (Schimper) Amann, Fl. Mouss. Suisse 1:188. 1912


Limnobium norvegicum Schimper, Bryol. Eur. 6:70. 576. 1853; Calliergon viridulum (Lindberg) Kindberg; Limnobium viridulum (Lindberg) Kindberg; Ochyraea norvegica (Schimp.) Ignatov & Ignatova


Plants in small, soft, loosely to tightly woven patches, pale yellow green, light brown with age.  Stems to 3 cm, usually less than 1.5 cm, branching irregular; hyalodermis absent, central strand present. Leaves when wet, straight and loosely imbricate to spreading, crisping upon drying to shrinking laterally and concomitantly inrolling and twisting, usually ovate, less often broadly ovate, plane to shallowly but clearly concave, (0.4--)0.5--0.8(--0.9) x (0.2--)0.4--0.5(--0.6) mm; apex acute, occasionally obtuse, sometimes slightly squarrose, margins entire, usually plane, or rarely narrowly recurved, mostly in the proximal 1/4 of the leaf, rarely reaching the shoulder before the apex; basal cells variable; alar cells undifferentiated or forming a small, irregular group of a few quadrate to short-rectangular cells; medial cells short-rhombic, bacilliform, fusiform, to linear-flexuose, (16--)20--30(--48) x 5--6 \um; apical and marginal cells shorter.  Sexual condition  autoicous, inner perichaetial leaves lanceolate, acute or gradually tapering, costa slender, single or double to midleaf, 2--4 plicae, cells smooth, margins entire or finely and irregularly toothed.  Seta 6--10 mm, yellow to reddish brown.  Peristome endostome with 2--3 well-developed cilia.


Irrigated acidic rocks in montane streams; moderate to high elevations, 650--1700 m; B.C.; Alaska; Greenland, Europe (Scandinavia).


Hygrohypnum norvegicum remains a poorly understood species.  Eight North American specimens are too few from which to develop a sound concept of its distinctiveness and variability. The lone specimen from B.C. looks like a very tiny H. molle. There are some very small specimens of H. cochlearifolium with which the B.C. specimen could be confused.  In combination these characters serve to distinguish H. norvegicum: tiny, ovate leaves with acute apices, and loosely imbricate to spreading leaf stance.


12. Hygrohypnum ochraceum (Turner ex Wilson) Loeske, Moosfl. Harz., 321. 1903


Hypnum ochraceum Turner ex Wilson, Bryol. Brit., 400, plate 58. 1855; Calliergon ochraceum (Turner ex Wilson) Kindberg; Hygrohypnella ochracea (Turner ex Wilson) Ignatov & Ignatova; Hygrohypnum ochraceum var. filiforme (Limpricht) Amann;  H. ochraceum var. flaccidum (Milde) Amann; H. ochraceum var. uncinatum (Milde) Loeske


Plants soft or coarse, bright shiny yellow-green, dull yellow-green, bright or dull green, dull olivaceous green with or without rusty mottling, dirty brown, rarely blackish or blackish green.  Stems to 15 cm, prostrate and creeping or ascending at the tip, tips straight or hooked, generally foliose throughout or with shredded leaf-bases or denuded in the older extremities, unbranched or irregularly branced, hyalodermis present as a single epidermal layer of inflated, thin-walled, hyaline cells enclosing a cortex of 2--3 rows of small, thick-walled yellow to reddish brown cells, central strand well-developed. Leaves variable among different plants or within individual stems or branches, crowded or distant, loosely imbricate or spreading, straight or falcate; ovate-lanceolate or lanceolate, infrequently ovate, rarely broadly-ovate, (0.7--)1--1.8(--2.5) x

(0.2--)0.5--0.8(--1.2) mm, apex acute to long, tapering acuminate, obtuse or bluntish, margins entire except where minutely denticulate to serrulate in the apex; costa variable, almost absent, short and double, usually long and double with one or both arms reaching mid-leaf or beyond or single to mid-leaf or beyond, or single to mid-leaf or beyond or single with 1--3 lateral forks; basal cells variable, usually wider but variously shorter, longer or changing little from medial cells, becoming incrassate in age; alar cells variable, quadrate, short-rectangular or sometimes linear, thin-walled or slightly thickened, hyaline, almost never discolored, forming an irregular group in 2--3 rows along the margin, the marginal row of which forms a variable group of 3--4 or 5--7 cells that gradually transition from quadrate or short-rectangular at the insertion to rectangular or linear further up the margin, medial cells fusiform to linear, long-flexuose, (30--)37--83(--120) x (4--)5--6(--8) \um, marginal cells shorter toward the apex, but variable elsewhere. Sexual condition dioicous, inner perichaetial leaves long-tapering lanceolate, minutely serrulate at the apex, plicate, cells smooth, costa variable. Seta 16--31 mm, reddish brown. Peristome endostome with 1--3 cilia.


Irrigated acidic rocks and wood in streams; low to very high elevations, 200--3700 m; Greenland; Alta., B.C., Ont., N.B., Nfld. (Nfld.), N.S. Que., Yukon; Alaska, Ariz., Calif., Colo., Conn., Idaho, Mass., Md., Maine, Mich., Mont., N.H., N.J., Oreg., Pa., R.I., Utah, Vt., Va., Wash., W.Va., Wyo.; Europe; Asia; Atlantic Islands (Iceland).


Hygrohypnum ochraceum is highly polymorphic. It varies from compact specimens with falcate-secund leaves to those with long, trailing stems with straight, widely spaced leaves. Unifying such plants is their dioicous sexuality and a stem hyalodermis.  With experience the need to cut stem cross-sections can be circumvented by observing the marginal alar cells just above the point of insertion. The most proximal cell is generally quadrate or very short-rectangular while those above grade to longer rectangular to almost linear.  Hygrohypnum ochraceum has often been confused with H. luridum, which differs in being autoicous, a calcicole, lacks a hyalodermis, and has a well-developed group of quadrate to short-rectangular or irregular alar cells.


13. Hygrohypnum polare (Lindberg) Loeske, Verh. Bot. Ver. Brandenburg  46: 198. 1905


Hypnum polare Lindberg, Oefv. K. Ak. Foerh. 23:540. 1867; Calliergon polare (Lindberg) Kindberg; Hygrohypnella polaris (Lindberg) Ignatov & Ignatova; Hygrohypnum palustre var. ehlei (Arnell) Grout


Plants in appressed turfs or loose patches, golden-yellow, yellowish green, rarely bright green.  Stems to 13 cm, prostrate, ascending or erect, branching absent or irregular from the base, mostly fastigiate; hyalodermis incomplete, an outer row of thin-walled cortical cells, evident in older stems only as the thickened inner concave walls, central strand well-developed, discolored in age.  Leaves appressed-imbricate to loosely spreading, differing wet or dry, ovate-lanceolate, oblong-lanceolate, elliptic or broadly so, straight or falcate, shallowly to deeply concave, rarely almost plane, (0.9--)1.1--1.6(--2.1) x (0.6--)0.75--1(--1.1) mm;  apex tapered to an acute or apiculate point, or deeply concave-cucullate with an often recurved apiculus; margins entire and plane, sometimes slightly inrolled near the apex, margins in falcate leaves inrolled rendering the leaf tubulose in the distal half; costa very stout, single, ending shortly below the apex, or percurrent in the apiculus,  rarely forked, never short and double; basal cells shorter and wider than medial cells, incrassate and yellowing in age, alar cells numerous, in a well-defined group of quadrate or short-rectangular, usually thin-walled, hyaline cells, becoming brown in age; median leaf cells fusiform to long, linear-flexuose, (33--)40--50(--65) x 5--6(--8) \um; apical cells shorter, usually rhomboid.  Sexual condition dioicous; inner perichaetial leaves long-lanceolate, plicate, costa single and strong, cells smooth, apex gradually tapering, becoming frayed in age. Seta 10--12 mm.  Peristome unknown.


Acidic rocks in montane or high latitude streams; moderate elevations, 900--1400 m; Greenland; B.C., Nfld. (Nfld.), Nunavut; Alaska; Europe, Asia (Russia).


Hygrohypnum polare is easily recognized by the strong, single costa and the outer layer of thin-walled cortical cells in the stem. The group of quadrate alar cells and the usual leaf concavity provide confirmation.


14. Hygrohypnum smithii (Swartz in Liljeblad) Brotherus. Natürl.. Pflanzenfam. 1(3):1039. 1909


Leskea smithii Swartz in Liljeblad. Svensk. Fl., ed. 3, 549. 1816; Calliergon arcticum (Sommerfelt) Kindberg; Hypnum torrentis Müll. Hal. & Kindberg in Macoun; Ochyraea smithii (Swartz in Liljeblad) Ignatov & Ignatova


Plants very coarse and stiff. dull, dark green, olivaceous green, or black, all with or without golden-green or golden-brown mottling. Stems to 8 cm, branching absent or irregular, proximal stems and branches denuded or with persistent, shredded leaf bases, hyalodermis absent, central strand well developed.  Leaves stiffly and loosely imbricate to erect-spreading, shrinking and twisting upon drying, usually broadly ovate, elliptical or orbicular, sometimes ovate, transverse or triangular, plane or shallowly concave, (0.6--)0.8--1.2(--1.5) x (0.4--)0.6--1.2(--1.4) mm; apex usually obtuse or rounded; margins entire or weakly denticulate; costa stout, single to 3/4\x leaf length, often forked, occasionally short and double; basal cells generally wider, longer, and more incrassate than medial cells, also yellowing; alar cells quadrate to rectangular, incrassate and yellowing, not forming a clearly recognizable or differentiated group; medial cells rhomboid, fusiform to short, linear-flexuose, 22--48(--64) x (4--)5--7(--10) \um; apical cells rhombic or rounded; margins often bordered by an ill-defined row of short cells. Sexual condition autiocous, inner perichaetial leaves lanceolate, costa strong and single, margins entire, cells smooth, apex acute or obtuse, with or without a few teeth. Seta 8--17 mm, red or brown. Peristome endostome with 1--3 poorly to well developed cilia.


Irrigated to emergent acidic rocks in montane streams, occasionally on rocks or wood in slow moving water or ponds; moderate to very high elevations, 550--3100 m; Alta., B.C., Nfld. (Nfld.), N.S., Que.; Alaska, California, Colo., Mont., Wash.; Greenland; Atlantic Islands (Iceland), Europe. 


Hygrohypnum smithii is a well-defined species, easily recognizable by its coarse, rigid habit, usually broadly-ovate to orbicular leaves, and stout, usually single costa.


15. Hygrohypnum styriacum (Limpricht) Brotherus, Natürl. Pflanzenfam. 1(3):1039. 1909


Hypnum styriacum  Limpricht, Flora (Jena) 65: 201. 1882; Eurhynchium styriacum (Limpricht) Kindberg


Plants soft to slightly rigid, usually dull yellow-green with rusty mottling, less often dirty, brownish yellow or uniformly dull green.  Stems to 6 cm, foliose throughout or denuded in older extremities, branching irregular, hyalodermis absent, central strand strong. Leaves slightly crowded to clearly distant, spreading when wet, or slightly falcate, upon drying shrinking laterally and twisting apically or spreading, weakly imbricate or falcate, ovate, straight or falcate, broadly concave when wet, (0.7--)1--1.75(--2) X (0.3--)0.5--1(--1.1) mm, apex abruptly acuminate, less often gradually so, sometimes sharply reflexed, apex and margin entire; costa strong and thick, short and double, single or forked, or infrequently single beyond mid-leaf; basal cells slightly wider than medial cells; alar cells undifferentiated or recognizable as a few quadrate or short-rectangular cells grading imperceptibly into other basal or proximal medial cells; medial cells generally short, variously rhombic, short-fusiform or bacilliform, thick-walled, (18--)28--40(--50) x (4--)5--7(--9) \um; cells toward the margins or apex little changed or shorter. Sexual condition autoicous, a single perigonium situated immediately beside a single perichaetium or between 2--4 perichaetia, in all cases the perigonial-perichaetial complex is enclosed within 2--3 small bracts, this complex borne in the axil of a vegetative leaf. Seta 9--21 mm, reddish yellow to red. Peristome endostome of 2--3 sometimes poorly developed cilia.


Irrigated, emergent acidic rocks in montane streams; high to very high elevations, 2000--3700 m; Alta., B.C.; Calif., Colo., Idaho, Mont., Utah, Wyo.; Europe.


Hygrohypnum styriacum is a distinctive species, but one sometimes mistaken for small, falcate-leaved forms of H. luridum. At present this is only a problem in western North America where the two species are sympatric. Hygrohypnum styriacum leaves are characteristically ovate to slightly broadly so, but with an abruptly acuminate apex. In contrast, falcate-leaved forms of small specimens of H. luridum have leaves that taper gradually to an acute point from an ovate or oblong-lanceolate proximal lamina. Though a subtle trait, the costa of H. styriacum is slightly stouter than those of H. luridum.  All leaves of H. luridum have a well-developed group of quadrate to short-rectangular of irregular alar cells, whereas the alar cells of H. styriacum are undifferentiated or composed a few quadrate or short-rectangular to irregular cells that grad imperceptibly into adjacent cells. The capsule has a deciduous annulus of 1--2 rows of cells. If available for examination a differentiated annulus may be found upon lifting the operculum of H. styriacum, while such an annulus in absent in H. luridum. Hygrohypnum luridum occurs strictly on calcareous rocks or rocks of other types but irrigated by calcareous water, while H. styriacum, like all other species of the genus, occupies acidic substrates.


The perichaetia and perigonia are typically remote from each other in autoicous species of the genus.  Hygrohypnum styriacum is also autoicous, but in H. styriacum a single, normal perigonium is found beside a single, typically formed perichetium or between 2--4 perichaetia. In all cases the complex is subtended or enclosed by 2--3 small bracts, and the whole is borne in the axil of a single vegetative leaf.


16. Hygrohypnum subeugyrium (Renauld & Cardot) Brotherus, Natürl. Pflanzenfam. 1(3): 1039. 1909


Hypnum subeugyrium Renauld & Cardot, Bot. Gaz. 22: 52, plate 4. 1896; Calliergon subeugyrium (Renauld & Cardot) Kindberg; H. eugyrium var. subeugyrium (Renauld & Cardot) Grout; H. eugyrium var. miquelonense (Renauld & Cardot) Grout; Pseudohygrohypnum subeugyrium (Renauld & Cardot) Ignatov & Ignatova


Plants at stem and branch tips yellow-green, bright green or dark, metallic-red, becoming reddish brown, maroon-red, reddish black or brownish black in older extremities. Stems to 6 cm, extremities mostly denuded, branching irregular, hyalodermis absent, central strand poorly developed or absent.  Leaves little different wet or dry, straight, loosely imbricate or falcate-imbricate, sometimes slightly complanate, narrowly ovate to ovate or oblong to oblong-lanceolate, falcate-secund or straight, symmetrical or sometimes asymmetrical, (0.9--)1--1.5(--2) x (0.3--)0.5--0.7(--0.8) mm, shallowly concave in broad leaves to deeply so in narrower leaves, margins entire and plane, apex gradually to abruptly acute to slightly acuminate tip, apical margins are usually entire, but most stems and branches will exhibit a few leaves that have abruptly acute apices that are slightly denticulate or serrulate; costa slender, short and double, or absent, rarely single and slender; basal cells shorter and wider that medial cells, alar cells variable, nearly undifferentiated or forming an irregular group of quadrate, short-rectangular or irregular, strongly incrassate, yellowish or reddish brown cells, or exhibiting a basal row of enlarged incrassate cells surrounded by a few quadrate or irregular cells, medial cells long, linear-flexuose, (40--)45--80(--114) x (4--)5--6(--7) \um, becoming shorter toward the apex. Sexual condition autoicous, inner perichaetial leaves ovate-lanceolate to long, triangular-lanceolate, to 5 mm, erect, costa absent, short and double or single to mid-leaf, margins entire save a few fine apical teeth, cells smooth. Seta 13--22 mm, annulus present. Peristome exostome with 1--3 well-developed cilia.


Acidic rocks in streams; low to moderate elevations, 0--1500 m; St Pierre and Miquelon; Nfld. (Nfld.), N.B., N.S., Ont., Que.; N.H., N.Y., Tenn.; Europe.


Hygrohypnum subeugyrium is an enigmatic species I am not at all convinced truly belongs in the genus. In any event, H. subeugyrium can be identified by the combination of dark pigmentation, alar differentiation, and leaf tip morphology. Save for stem and branch tips, the older extremities of this species are darkly pigmented reddish brown, reddish black or brownish black. The transition from the yellow-green stem and branch tips to the darker, older extremities can be quite abrupt.  Alar differentiation is clear, but variable even among leaves on the same axis. They may form an irregular group of quadrate or short-rectangular shaped, strongly incrassate, yellowish or reddish brown cells or, as a basal row of enlarged, incrassate cells surrounded by a few that are quadrate or short-rectangular, both alar expressions may be excavated. Such alar cells are clearly different from the regularly inflated alar cells of H. eugyrium. The most important identifying feature is the leaf apex, but 10 to 20 leaves from 1 or 2 stems must be examined as a unit. Here, H. subeugyrium is most easily recognized by the regular occurrence of a few leaves with an abruptly acute leaf apex that are minutely denticulate to finely serrulate among other leaves with entire apical margins.