BFNA Title: Isopterygiopsis
Author: R. R. Ireland
Date: May 30, 2003
Edit Level: R Brum+
Version: 2

Bryophyte Flora of North America, Provisional Publication
Buffalo Museum of Science
1020 Humboldt Parkway
Buffalo, NY 14211 USA


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Hypnaceae - Isopterygiopsis


XXX. ISOPTERYGIOPSIS  Z. Iwatsuki, J. Hattori Bot. Lab. 33: 379.  1970.   [Greek iso, equal, pteron, winged, and opsis, appearance]


Robert R. Ireland


Plants small, sometimes complanate, in thin to dense, light- to yellowish-green glossy mats.  Stems 1--2 cm, creeping, simple or sparingly and irregularly branched, epidermal layer of stem cells small to large,  with thin exterior walls and thick interior ones, central strand sometimes present; rhizoids papillose, in clusters in leaf axils; axillary hairs hyaline, with one short-rectangular basal cell and two elongate apical cells; paraphyllia and pseudoparaphyllia lacking. Leaves of stems and branches similar, somewhat rigid, crowded and imbricate, erect-spreading, occasionally secund, sometimes complanate and pectinate, smooth, flat or somewhat concave, symmetric, nondecurrent, lanceolate or ovate- to oblong-lanceolate, long-acuminate to abruptly acuminate; margins plane to erect, entire or minutely serrulate; costa lacking or short and double; cells often flexuose, firm-walled, linear-fusiform, smooth or minutely prorulose at distal and proximal ends on dorsal leaf surface, with walls not pitted; alar cells not differentiated or sometimes with 1--3 quadrate to short-rectangular cells on margins.  Specialized asexual reproduction sometimes present as brood bodies in clusters in leaf axils on stems and branches, cylindric or fusiform, 28--96 ´ 5--14 µm, composed of 2--6 smooth cells.  Sexual condition autoicous or dioicous; perigonia and perichaetia clumped at base of stems and branches, bracts small, lanceolate to ovate, acuminate to abruptly filiform-acuminate, margins plane.  Seta solitary, red to reddish brown, 0.6--2 cm, twisted, straight to somewhat curved, smooth.  Capsule erect to cernuous, straight to subarcuate, yellow to light- or orange-brown, oblong to ovoid, smooth, contracted below mouth and wrinkled at neck when dry; annulus of 2--3 rows of cells, deciduous; operculum conic to obliquely rostrate, shorter than urn; stomata sparse, present in the neck, superficial; peristome double, exostome teeth cross-striolate proximally, papillose distally, bordered, trabeculate on interior surface; endostome with a high to low basal membrane, keeled segments, cilia shorter than segments, in groups of 1--3, sometimes absent. Calyptra cucullate, smooth, naked.  Spores spherical to ovoid, smooth or minutely papillose.


Species 3 (3 in the flora): North America, South America, Europe, Asia, Africa, Pacific Islands (New Zealand).


Plants of this genus occur in terrestrial habitats in boreal and temperate woods, as well as in the Arctic.


SELECTED REFERENCES   Ireland, R. R.  1969.  A taxonomic revision of the genus Plagiothecium for North America, north of Mexico.  National Museums of Canada, Nat. Mus. Nat. Sciences, Publs. in Botany 1: 1--118.  Iwatsuki, Z.  1970.  A revision of Plagiothecium and its related genera from Japan and her adjacent areas, I.  J. Hattori Bot. Lab. 33: 331-- 380.  Iwatsuki, Z.  1987.  Notes on Isopterygium Mitt.  (Plagiotheciaceae).  J. Hattori Bot. Lab. 63: 445--451.  Vitt, D. H.  1990.  The distribution of North American bryophytes Isopterygiopsis muelleriana (Schimp.) Iwat.  Evansia 7: 13--14.


1.  Plants complanate-foliate, pectinate, appearing ventrally concave because of curvature of upturned leaves; leaves often abruptly acuminate . . .   1.  Isopterygiopsis  muelleriana

1.  Plants not complanate-foliate; leaves gradually acuminate.

2.  Leaf margins entire or minutely serrulate near apex, often 1--2 cells serrulate in alar region; median leaf cells 96156 µm . .. 2.  Isopterygiopsis pulchella

 2.  Leaf margins serrulate in distal half; median leaf cells 33--61 µm. . . . 3.  I. alpicola


1.  Isopterygiopsis muelleriana (Schimper) Z. Iwatsuki, J. Hattori Bot. Lab. 33: 379.  1970


Plagiothecium muellerianum Schimper, Syn. Musc. Eur. (Ed. 1) 584.  1860; Isopterygium muellerianum (Schimper) Jaeger


Plants in thin mats, yellowish green, glossy.  Stems to 20 ´ 0.8--2 mm, complanate-foliate, pectinate, appearing concave because of curvature of upturned leaves, simple or irregularly branched; epidermal layer of stem cells large, thin-walled, enclosing 1-several layers of small, thick-walled cortical cells in the center. Leaves somewhat rigid, crowded and overlapping, erect-spreading and rigidly complanate, smooth, 0.5--1.5 ´ 0.2--0.4 mm, ovate- to oblong-lanceolate, symmetric, acuminate, often abruptly so, margins plane, entire or minutely serrulate; median cells 55--94 ´ 3--6 µm; alar cells not differentiated or sometimes with 1--3 short-rectangular cells only on margins, 8--24 ´ 4--7 µm.  Specialized asexual reproduction sometimes present as propagules, 66--96 ´ 6--12 µm, composed of 2--6 cells, green to yellowish green.  Sexual condition dioicous.  Seta brown to reddish brown, 0.6--1.2 cm.  Capsule yellowish brown to orange-brown, erect or rarely ± cernuous, straight, 0.5--1.5 ´ 0.2--0.4 mm, ellipsoid to ovoid, contracted below mouth when dry; operculum conic to obliquely rostrate, 0.4--0.8 mm.  Spores 8--12 µm.


Capsules mature fall (Sept.).  Acidic cliffs, rock outcrops and boulders in woods; 360--1160 m; B.C., N.B., Nfld, N.W.T., N.S., Ont., Que., Yukon; Alaska, Ark, Conn., Ill., Ky., Maine, Md., Mich., Minn., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Utah, Vt., Va., Wis.; Mexico (Distrito Federal); Europe; Asia.


Isopterygiopsis muelleriana is easily distinguished from the other two species in the genus by stems that are complanate-foliate, pectinate, appearing concave on the adaxial surface because of the upturned leaves, and by its epidermal stem cells that are very large and thin-walled. The Utah record is from S. Flowers (1973).


2.  Isopterygiopsis pulchella (Hedwig) Iwatsuki, J. Hattori Bot. Lab. 63: 450.  1987 


Leskea pulchella Hedwig, Spec. Musc. 220.  1801; Holmgrenia diminutiva Grout; Hypnum nitidulum Wahlenberg; Isopterygium pulchellum (Hedwig) Jaeger; I. pulchellum var. nitidulum (Wahlenberg) Roth; Orthothecium diminutivum (Grout) H. Crum, Steere & L. E. Anderson; Plagiothecium passaicense Austin; P. pseudolatebricolum Kindberg; P. pulchellum (Hedwig) Bruch, Schimper & W. Gümbel



Plants in thin to dense mats, light- to yellowish-green, glossy.  Stems to 20 ´ 1--2 mm, simple or irregularly branched; epidermal layer of stem cells somewhat large with thinner exterior walls than interior, 1-several layers of smaller inner thick-walled cortical cells.  Leaves flaccid, close or sometimes distant, erect-spreading, occasionally secund, often appearing distichous, subconcave, smooth, 0.5 --1.5 ´ 0.2--0.4 mm, lanceolate to slenderly ovate-lanceolate, symmetric, gradually long-acuminate, margins plane to erect throughout, entire or sometimes minutely serrulate at apex, often with 1--2 cells distinctly serrulate in alar region; median cells 96--156 ´ 5--7 µm; alar cells differentiated only on margins, 1--3 quadrate to short-rectangular cells, 16--31 ´ 7--9 µm, sometimes lacking.  Specialized asexual reproduction rarely present, propagules, 33--61 ´ 9--14 µm, composed of 2--5 cells, green to yellowish green.  Sexual condition autoicous.  Seta red to reddish brown, 1--2 cm.   Capsule yellow to orange-brown, subcernuous to cernuous, rarely erect, straight to subarcuate, 0.5--2.5 mm, oblong to ovoid, contracted below mouth when dry; operculum conic to conic-apiculate, 0.2--0.3 mm.  Spores 914 µm.


Capsules mature spring to late summer.  Acidic cliff crevices, rocky banks, sometimes calcareous soil and soil on overturned tree roots, bases of trees, decaying wood; 15--2270 m; Greenland; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Nun., Ont., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Maine, Mich., Minn., Mont., N.H., N.J., N. Mex., N.Y., Oreg., Pa., S.Dak., Utah, Vt., Wash., Wyo.; Mexico (Veracruz); South America (Argentina, Chile); Europe; Asia; Africa; Pacific Islands (New Zealand).


Isopterygiopsis pulchella is autoicous, and often produces sporophytes, while the other two species of Isopterygiopsis are dioicous and usually sterile.  This species is further distinguished by the erect-spreading, sometimes secund, lanceolate to slenderly ovate-lanceolate, gradually acuminate, nondecurrent leaves with entire or minutely serrulate margins at the apex and base.


The epidermal stem cells of I. pulchella and I. alpicola are scarcely enlarged, only somewhat thin-walled and not as distinctly differentiated from the interior cortical cells as those of the type species of Isopterygiopsis, I. muelleriana.  All three species, however, have papillose rhizoids in the leaf axils, as well as clusters of 26 celled cylindrical or fusiform gemmae in the leaf axils, and both characters readily place them in Isopterygiopsis. Orthothecium intricatum (C. J. Hartman) Schimper and O. strictum Lorentz may be confused with I. pulchellum in the Arctic but both species are dioicous and rarely produce sporophytes.  Also, plants of Orthothecium have mostly straight, erect-spreading leaves rather than secund leaves like I. pulchellum.  The Utah record is that of S. Flowers (1973). William Weber (personal communication) noted that Orthothecium diminutivum (Grout) H. Crum, Steere &L. E. Anderson (Holmgrenia diminutiva Grout) described from Colorado is synonymous with I. pulchella  because of its papillose rhizoids and its multicellular, cylindrical brood bodies.



3.  Isopterygiopsis alpicola (Lindberg & Arnell) Hedenäs, J. Bryol. 15: 495.  1988


Stereodon alpicola Lindberg & Arnell, K. Svensk. Vet. Ak. Handl. 23(10): 1890 ; Amblystegiella alpicola (Lindberg & Arnell) Brotherus; Amblystegium alpicola (Lindberg & Arnell) Mönkemeyer; Isopterygium alpicola (Lindberg & Arnell) Nyholm; Pylaisia alpicola (Lindberg & Arnell) Limpricht


Plants in thin to dense mats, light- to yellowish green, glossy.  Stems to 10 ´ 1 mm, simple or irregularly branched; epidermal layer of stem cells with exterior walls thinner than those of the 1-several layers of interior walled cortical cells.  Leaves flaccid, close to somewhat distant, erect-spreading, concave, smooth, 0.3--0.8 ´ 0.1--0.3 mm, ovate-lanceolate, symmetric, gradually acuminate, margins plane to erect, distinctly serrulate; median cells 33--61 ´ 5--9 µm; alar cells differentiated, quadrate to short-rectangular, 14--28 ´ 7--9 µm.  Specialized asexual reproduction rarely present, propagules, 28--47 ´ 9--14 µm, composed of 2--5 cells, green to yellowish green, smooth.  Sexual condition dioicous.  Sporophytes unknown.


Calcareous rocks and cliffs; 3,000 m or above; Nun. (Seymour I.); Alaska (Arctic Village, Point Barrow), Colo. (Summit Co.); Europe.


Isopterygiopsis alpicola is an Arctic-alpine species that is rare or seldom collected.  R. Tuomikoski (1939) was apparently the first to note the close relationship of this species to I. pulchella.  The shorter, broader leaf cells and the serrulate leaf margins of I. alpicola are the only notable differences distinguishing it from I. pulchella.




Flowers, S.  1973.  Mosses: Utah and the West.  Plagiothecium, pp. 520--524.  Provo.

Tuomikoski, R.  1939.  Materialien zu einer Laubmoosflora des Kuusamo-Gebietes.  Ann. Bot. Soc. Fenn. Vanamo 12(4): 1--124.