BFNA Title: Scleropodium
Author: M. S. Ignatov
Date: October 3, 2009
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden

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XX. Scleropodium Bruch, Schimper & Gümbel, Bryol. Eur. 6: 27. 1953.  *  [Greek sclero, rigid, and podium, seta, alluding to stiff seta]

Michael S. Ignatov


Plants medium-sized to robust, in more or less loose tufts, green to yellowish or brownish green, glossy. Stems prostrate, with central strand, densely foliate to cochleariform, irregularly and mostly sympodially branching; branches similar to stems; axillary hairs 2--4-celled; juvenile branch leaves triangular, acute. Stem leaves usually closely imbricate, appressed when dry and wet, rarely erect when wet (S. californicum), broadly ovate to ovate-lanceolate, obtuse, acute, short–acuminate, rarely long-acuminate; rounded to base, inconspicuously decurrent; strongly concave, non-plicate; margin plane or recurved near base, serrulate to subentire; costa reaching 0.6--0.8\x the leaf length, usually ending in an indistinct abaxial spine, rarely smooth (S. obtusifolium); basal cells short to elongate, more or less thick-walled, this sometimes making the leaf difficult to detach, alar cells isodiametric, larger, thin- to thick-walled in a rather small group; laminal cells flexuose-linear, thick-walled. Branch leaves similar to stem leaves. Sexual condition dioicous; perichaetial leaves abruptly contracted from a sheathing base into long, reflexed acumens. Seta red-brown, rough throughout or only distally, or smooth. Capsule red-brown, inclined to horizontal, rarely suberect to inclined (S. caespitans); annulus separating or not; operculum conic; peristome xerocastique, perfect, cilia appendiculate or rarely nodose (S. caespitans). Spores 11--19 \um. Calyptra naked.


Species: 5--10 (5 in the flora): w North America, w Eurasia, n Africa, Atlantic Islands, and the taxonomic status of East Asian and Australian species within the genus need confirmation.


SELECTED REFERENCES: Lawton, E. 1967. Notes on Scleropodium, with the description of a new species. Bull. Torrey Bot. Club 94: 21--25.


1.         Stem leaves broadly ovate-oblong, lacking pointed apex or point indistinct; subaquatic plants; costa lacking a terminal spine. . . 5. Scleropodium obtusifolium

1.         Stem leaves ovate to lanceolate, obtuse, acute, or short-acuminate; terrestrial, epiphytic, or epilithic, usually from rather xeric or mesic habitats; costa ending in a small abaxial terminal spine.

2.         Cells across leaf base elongate, ca. 3--6:1, in 2--3 rows; plants medium-sized to rather robust, leaves to 0.6--1 mm wide . . .  4. Scleropodium touretii

2.         Cells across leaf base quadrate to short rectangular, ca. 1--3:1, in 3--4 rows; plants small to medium-sized (S. caespitans), leaves to 0.3--0.6 mm wide.

3.          Leaves acuminate . . . 1. Scleropodium californicum

3.          Leaves obtuse, acute, or short-acuminate.

4.          Shoots strongly julaceous, 0.3--0.4 mm wide; leaves broadly acute or obtuse, 0.7--0.9(--1.2) x 0.5--0.6(--0.7) mm, with length to width ratio usually 1.2--1.5:1 . . . 2. Scleropodium julaceum

4.          Branches moderately or sometimes strongly julaceous; 0.6--0.9 mm wide; leaves acute or shortly acuminate, 0.8--1.6 x 0.3--0.8 mm, with length to width ratio 1.6--2.6:1 . . . 3. Scleropodium caespitans


1. Scleropodium californicum (Lesquereux) Kindberg, Enum. Bryin. Exot., 35. 1888


Hypnum californicum Lesquereux, Trans. Amer. Phil. Soc. n. s. 13: 13. 1865


Plants small to medium-sized, in rather loose, thin mats, green to yellowish green. Stems to 5 cm, procumbent with ascending tips; shoots with leaves, when dry, ca. 0.3 mm wide; branches erect, filiform. Stem leaves loosely imbricate, appressed when dry (except for the slightly reflexed acumen), erect when wet, 0.8--1.2 x 0.3--0.4(--0.5) mm, ovate-lanceolate, acute to acuminate, margin serrate to serrulate, occasionally subentire; basal juxtacostal cells either ca. 10--30 x 5--10 \um, or similar to alar cells in 1--3 rows; alar cells isodiametric, mostly irregularly polygonal, variable in size, 6--13 \um, forming an extensive triangular group, usually reaching the costa, sometimes reaching halfway to costa, indistinctly delimited from neighboring cells; mid leaf cells 30--65 x 4--6 \um, with obtuse ends. Seta 15 mm, rough distally, smooth to slightly rough proximally. Capsule inclined, curved. Spores 10--14 \um.


Soil on rocks in sunny places; 0--900 m; Calif.; Mexico (Baja California).


Scleropodium californicum is similar Brachythecium albicans but has distinctly thinner shoots. In anatomical details, it differs in having short laminal cells, opaque basal cell groups, and serrate or serrulate margins, at least distally. From the other species of Scleropodium, it differs in being less julaceous when dry and grows in loose, thin mats.


2. Scleropodium julaceum E. Lawton, Bull. Torrey Bot. Cl. 94: 22. 1967


Plants small, in moderately dense mats, green to golden green. Stems 2--5 cm, procumbent, rather fragile; shoots 0.3--0.4 mm wide; branches similar to stem. Stem leaves closely imbricate, tightly appressed when dry, erect and slightly spreading when wet, 0.7--0.9(--1.2) x 0.5--0.6(--0.7) mm, with length to width ratio usually 1.2--1.5:1, broadly ovate to semi-orbicular, broadly acute or obtuse in smaller leaves; margin more or less serrulate in distal portion of leaf, sometimes almost entire throughout; basal juxtacostal cells 8--10(--12) \um in 2--5 rows, quadrate, moderately thick-walled, alar cells forming a triangular group moderately distinctly delimited from neighboring cells, extending 7--9 cells along margin; mid leaf cells 20--60 x 5--9 \um, rhombic to linear-flexuose. Seta 6--7 mm, rough throughout. Capsule horizontal. Spores ca. 12--19 \um.


Rosks, tree trunks, rather open and sunny places; 0--500 m; Calif.


Scleropodium julaceum occurs only in southern California, with scattered localities north to Mendocino Co. This species often has broadly rounded leaves that easily distinguish it from other species in the genus. Small phenotypes of S. caespitans may be similar in appearance and leaf shape, but they differ in their alar cells, numerous and small in S. julaceum, but these few and enlarged in S. caespitans. Also, the capsule is horizontal in S. julaceum, whereas suberect in S. caespitans. Additionally, this species is superficially similar to Myurella julacea.


3. Scleropodium cespitans (Wilson ex Müller Hal.) L. F. Koch, Leafl. Western Bot. 6: 31. 1950


Hypnum cespitans Wilson ex Müller Hal., Synop. Musc. Frond. Cognit. 2: 355. 1851; Scleropodium caespitosum Wilson, S. apocladum (Mitten) Grout.



Plants medium-sized, in moderately dense extensive mats, green to brownish green. Stems to 10 cm, procumbent; shoots to 0.9 mm wide, branches often much thinner and only 0.4--0.5 mm wide; branches julaceous, more slender than in S. tourettii. Stem leaves closely imbricate and tightly appressed, 0.8--1.6 x 0.3--0.8 mm, with length to width ratio 1.6--2.6:1, ovate, acute or very shortly acuminate, rather weakly rounded to insertion; margin serrulate near apex, weakly serrulate to subentire proximally; basal juxtacostal cells in 2--3 rows short, 10--20 x 7--10 \um, moderately thick-walled, not colored; alar cells larger, 10--14 \um, pellucid, thin-walled, forming a small, compact group rather distinctly delimited from neighboring cells; mid leaf cells 30--65 x 4--6 \um, oblong, with obtuse angles. Seta to 12 mm, strongly to moderately rough throughout. Capsule suberect to inclined; cilia of endostome and to horizontal. Spores ca. 13--16 \um.


Tree bases, tree roots, rotten logs, occasionally rock; 0--1300 m; Alta., B.C.; Ariz., Calif., Oreg., Wash.; w Eurasia; n Africa; Atlantic Islands.


A number of characters separate Scleropodium cespitans from the widespread S. touretii, but when the latter is represented by small plants, then the most reliable distinction are characters of the leaf base: cells towards the leaf base in S. caespitans are reduced, and when the leaf separates only small remains of cells remain on the stem, whereas S. touretii has long and stiff basal cells, considerable portions of which are left on the stem when the leaf is detached (a similar pattern is commonly seen in Homalothecium).


4. Scleropodium touretii (Bridel) L. F. Koch, Rev. Bryol. Lichénol. 18: 177. 1949,  as “tourretii”


Hypnum touretii Bridel, Muscol. Recent. Suppl. 2: 185. 1812


Plants medium-sized, in rather loose, extensive tufts, green to yellow- or brownish green. Stems to 10 cm, procumbent; shoots 0.5--1.0 mm wide; branches julaceous and tumid to distantly foliate, often curved. Stem leaves closely imbricate, 0.9--1.5(--2) x 0.3--1, broadly ovate to ovate-oblong, rather abruptly narrowed to a short acumen or apiculus; margin serrulate distally, subentire proximally; basal juxtacostal cells 10--25 x 5--8 \um, elongate, thick-walled and often colored, larger quadrate cells sometimes occurring in one row below these cells; alar cells few, quadrate, somewhat larger than juxtacostal cells, 10--12 \um, with moderately thin walls, forming a small group, often undifferentiated; mid leaf cells 35--65(--90) x 3-5 \um. Seta 10--20 mm, strongly roughened throughout. Capsule inclined to horizontal, curved. Spores 11--14 \um.


Varieties 2 (2 in the flora): North America. Mexico (Baja California); w Eurasia; n Africa; Atlantic Islands.


Scleropodium touretii can be recognized by tumid and turgid foliage, and by short, but conspicuous, leaf apices that are filiform and often squarrose. There are difficulties separating S. touretii from S. obtusifolium and S. caespitans, see their discussions. Scleropodium colpophyllum is often treated as a separate species (e.g., D. H. Norris and J. R. Shevock (2004) and L. E. Anderson et al. (1990), while Lawton (1967) treated it as a variety of S. touretii. The latter point of view is accepted here because: (1) phenotypes with loosely arranged leaves are known also in S. obtusifolium and S. caespitans; (2) loosely foliate shoots can be found inside extensive mats of otherwise typical and well-developed  S. touretii; and (3) S. touretii var. colpophyllum occurs usually in more mesic and shaded habitats than S. touretii var. touretii, that is, in habitats where many mosses develop looser foliage. However additional studies are needed on the status of this taxon.


1. Branches julaceous, tumid and turgid; leaves deeply concave . . . 1. Scleropodium touretii var. touretii

1. Branches variable in foliage, some julaceous, but most of them with widely spreading leaves; leaves moderately concave  . . . 2. Scleropodium touretii var. colpophyllum


4a. Scleropodium touretii (Bridel) L. F. Koch var. touretii


Stems to 10 cm, procumbent; shoots 0.7--1.0 mm wide, strongly julaceous, curved. Stem leaves closely imbricate to distant, 0.9--1.5(--2) x 0.3--1 mm, strongly concave.


Shady grassy soil and shaded rocks; 0--1500 m; B.C.; Calif., Oreg., Wash.; Mexico (Baja California); w Eurasia; n Africa; Atlantic Isalnds.


4b. Scleropodium touretii (Bridel) L. F. Koch var. colpophyllum (Sullivant) E. Lawton, Bull. Torrey Bot. Cl. 94: 24. 1967


Eurhynchium colpophyllum Sullivant, Icones Musc., Suppl., 95, plate 71. 1874; Scleropodium colpophyllum (Sullivant) Grout


Stems to 10 cm, procumbent; shoots 0.5--10 mm wide, partly julaceous, mostly rather loosely foliate, straight to curved. Stem leaves closely imbricate to distant, 0.9--1.6 x 0.4--0.9 mm, moderately concave.


Soil banks and soil over rocks; occasionally on concrete and rotten logs; 300--1000 m; B.C.; Calif., Oreg., Wash.; Mexico (Baja California, Durango).


5. Scleropodium obtusifolium (Mitten) Kindberg, Cat. Canad. Pl., Part VI, Musci 202. 1892


Stereodon obtusifolius Mitten, J. Proc. Linnean Soc. 8: 42. 1864


Plants medium-sized to robust, in moderately loose extensive tufts, green to golden-green. Stems to 15 cm, procumbent or floating; branches julaceous, tumid, often arching. Stem leaves closely imbricate, 1.1--1.5 x 0.6--0.9 mm, broadly ovate to ovate-oblong, rather abruptly narrowed to the obtuse apex, margin slightly serrulate, although it often appearing entire due to incurved margin leaf margin; basal juxtacostal cells 10--25 x 5--7 \um, elongate, thick-walled; alar cells quadrate to short-rectangular, 10--15 x 10--12 \um, moderately thick-walled, forming small group indistinctly delimited from neighboring cells; mid leaf cells 40--65 x 5--6 \um. Seta 10--15 mm, strongly roughened throughout. Capsule inclined, curved. Spores 10--16.


Rock and soil in wet places, temporarily submerged, along stream and small creek banks; 0--2700 m; B.C.; Alaska, Ariz., Calif., Idaho, Mont., Nev., Oreg., Utah, Wash.; endemic.


The basal leaf cells and strongly tumid habit of Scleropodium obtusifolium are similar to that of S. touretii to which this species is obviously related. Leaf tips are obtuse in this species, but under a stereomicroscope or hand-lens they may appear somewhat pointed; microscopic examination is required in this case: in S. touretii the acumen is at least several cells in length, whereas the leaves of S. obtusifolium are obtuse, lacking an acumen.





Anderson, L. E., H. A. Crum, and W. R. Buck. 1990. List of the mosses of North America north of Mexico. Bryologist 93: 448--499.


Norris, D. H. and J. R. Shevock, 2004. Contributions toward a bryoflora of California: II. A key to the mosses. Madronõ 51: 133--269.


Grout, A. 1928. Moss flora of North America North of Mexico. Vol. 3. Part I. New York City, U. S. A.


Robinson, H. 1962 [1963]. Generic revisions of North American Brachytheciaceae. Bryologist 65: 73--146.