BFNA Title: Isopterygium
Author: R. R. Ireland 
Date: August 29, 2003
Edit Level: R Brum+
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden
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Isopterygium - Hypnaceae


X. ISOPTERYGIUM Mitten, J. Linn. Soc. Bot. 12: 21.  1869 *  [Greek iso, equal, and pteron, winged]


Robert R. Ireland


Plants small to medium-sized, in thin to dense, light- to yellowish-green glossy mats.  Stems 4--5 cm, creeping, simple or sparingly and irregularly branched, cortical cells small and thick-walled in cross section, surrounding larger, thinner walled cells, central strand usually absent; rhizoids smooth, on ventral surface of stems and branches just below juncture of leaves; axillary hairs with one brownish short-rectangular cell and one hyaline elongate apical cell; filamentous pseudoparaphyllia present, of 3--6 cells in 1 row or rarely with 2 rows at base.  Leaves of stems and branches similar, rigid or flaccid, crowded and imbricate to remote, erect-spreading or squarrose, commonly complanate-foliate, sometimes wrinkled and contorted when dry, smooth, flat or somewhat concave, symmetric or asymmetric, nondecurrent or rarely with 1--2 cells decurrent, ovate or lanceolate, acute to acuminate; margins plane to erect, sometimes recurved at base, serrulate above the middle, mostly entire below, sometimes entire throughout; costa short and double, sometimes lacking; cells often flexuose, thin to firm-walled, linear-fusiform, smooth, with walls not pitted or occasionally those of basal cells pitted; alar cells usually clearly differentiated, quadrate to rectangular, rarely transversely elongate.  Specialized asexual reproduction sometimes present on stems and branches, of uniseriate, often branched, filamentous, multicellular bodies with papillose cells.  Sexual condition autoicous or rarely dioicous; perigonia scattered along stems; perichaetia at base of stems, leaves oblong-lanceolate, gradually acuminate, margins plane.  Seta solitary, yellow, brown or reddish brown, 0.5--3 cm, usually twisted, straight to curved, smooth.  Capsule inclined to cernuous, sometimes erect, straight or arcuate when mature, brown to red-brown, cylindric, ovoid or ellipsoid, smooth, usually contracted below mouth and sometimes wrinkled at neck when dry; operculum conic to short-rostrate, shorter than urn; annulus lacking; peristome double, exostome teeth cross-striolate below, papillose above, bordered, trabeculate at back; endostome with high to low basal membrane, segments keeled, cilia shorter than segments, in groups of 1--3, sometimes lacking.  Calyptra cucullate, smooth, naked.  Spores spherical to ovoid, smooth or minutely papillose. 


Species 120--140 (2 in the flora) but many will undoubtedly be synonymous with other taxa after a worldwide revision; North America, Mexico, West Indies, Central America, South America, Europe (Italy), Asia, Africa, Pacific Islands, Australia.


Plants of this genus occur predominately in terrestrial habitats at low elevations in the subtropics and tropics.


SELECTED REFERENCES   Ireland, R. R.  1969.  A taxonomic revision of the genus Plagiothecium for North America, north of Mexico.  Natl. Mus. of Canada, Natl. Mus. of Natural Sci., Publ. in Bot., No. 1: 1--118.  Ireland, R. R.  1992.  The moss genus Isopterygium (Hypnaceae) in Latin America.  Tropical Bryology 6: 111--132.  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.  Iwatsuki, Z. and M. R. Crosby.  1979.  Lectotypification of the genus Isopterygjum Mitt.  J. Hattori Bot. Lab. 45: 389--393.  Redfearn, P. L., Jr.  1956.  Biometric analysis of the stem leaf variation of the Plagiothecium micans complex in southeastern United States.  Bryologist 59(4): 256--262.


1.  Plants small, stems seldom over 2 cm; leaves 0.7--1.2 × 0.2--0.6 mm, smooth or nearly so when dry; setae usually 0.5--1.5 cm . . . . 1.  Isopterygium tenerum

1.  Plants medium-sized, stems often 2--4 cm; leaves 1--1.5 × 0.4--0.7 mm, usually wrinkled and contorted when dry; setae 2--3 cm . . . . 2. Isopterygium tenerifolium


1.  Isopterygium tenerum (Swartz) Mitten, J. Linn. Soc. Bot. 12: 499.  1869


Hypnum tenerum Swartz, Fl. Ind. Occ. 3: 1817.  1806; H. albulum J. K. A. Müller; H. chapmanii Duby; H. fulvum Hooker & Wilson; H. micans Swartz; Isopterygium drummondii H. A. Crum, Steere & L.E. Anderson; I. fulvum (A. Jaeger) Kindberg; I. groutii (Cardot & Thériot ) Grout; I. micans (Swartz) Kindberg; I. micans var. latifolium (Grout) Schornherst; I. micans var. minus (Grout) H.A. Crum & L.E. Anderson; Isothecium tenerum (Swartz) Bridel; Plagiothecium fulvum A. Jaeger; P. groutii Cardot & Thériot; P. micans (Swartz) Paris; P. micans var. fulvum (A. Jaeger) Paris; Rhaphidostegium ludovicianum Renauld & Cardot; Rhynchostegium micans (Swartz) Austin


Plants in thin to dense mats, whitish- to yellowish-green.  Stems to 50 mm × 0.5--1.5(--3) mm, prostrate.  Leaves close, complanate, erect-spreading, often secund at tips, smooth, 0.7--1.8 × 0.2--0.6 mm, ovate to lanceolate, often asymmetric, acuminate; margins plane, serrate to serrulate above leaf middle, serrulate to entire below, rarely entire throughout; median cells 52--151 × 5--8 µm; alar cells short-rectangular to quadrate or transversely elongate, in small groups, 12--38 × 10--20 µm.  Specialized asexual reproduction sometimes present as filaments on stems, multicellular, simple or branched, often more than 0.5 mm, green or brown.  Sexual condition autoicous. Seta yellow to reddish brown, 0.5--1.5 cm.  Capsule light brown to orange-brown, cernuous, rarely erect, arcuate of sometimes straight, 0.5--2 × 0.2--0.5 mm, ovoid to ellipsoid, usually strongly contracted below the mouth when dry; operculum conic-apiculate to obliquely short-rostrate, 0.2--0.4 mm.  Spores 9--14 µm. 


Capsules mature spring--summer.  Dry wooded regions, swamps and wet roadside ditches, rotten logs, stumps, bases of trees, sandy soil; rarely on sedimentary rock; 0--360 m; N.S.; Ala., Ark., Del., D.C., Fla., Ga., Ky., La., Md., Mass., Miss., Mo., N.J., N.Y., N.C., S.C., Tenn., Tex., Va.; Mexico; West Indies; Central America; South America; Europe (Italy).


Isopterygium tenerum is common in Florida and the Gulf Coast, becoming infrequent northward, occurring in scattered localities to southern New York and disjunct to southern Nova Scotia. The species is extremely variable and several varieties have been described from North American plants.  These varieties, based on leaf shape and length, are believed to be environmental forms that are not worth formal recognition and are therefore included in the synonomy of I. tenerum.  P. L. Redfearn (1956), who did a biometric analysis on the stem leaf variation, reached a similar conclusion.  Isopterygium tenerum in its typical form is best distinguished by the usually complanate, small plants with stems 10--20 × 0.5--1.5 mm, filamentous pseudoparaphyllia, leaves ovate-lanceolate, asymmetric, acuminate, close, erect-spreading, 0.7--1.8 mm, alar cells in small groups of short-rectangular to quadrate or transversely elongate cells, asexual reproductive bodies sometimes present on stems, filamentous, multicellular, the cells papillose, setae 0.5--1.5 cm, and capsules ovoid to ellipsoid, inclined to horizontal, usually strongly contracted below the mouth when dry, 0.5--2.0 mm.


2.  Isopterygium tenerifolium Mitten, J. Linn. Soc. Bot. 12: 499.  1869


Plants in thin, loose mats, yellow-green to green.  Stems to 40 × 2--3 mm, prostrate.  Leaves close, complanate, wide-spreading to squarrose, smooth, usually wrinkled and contorted when dry, 1--1.5 × 0.4--0.7 mm, ovate-lanceolate to ovate, often curved and asymmetric, acuminate; margins plane to erect throughout, serrate to serrulate distally, serrulate proximally; median cells 71--141 × 5--7 µm; alar cells short-rectangular to quadrate, in small groups with 1--2 cells on margins, 19--33 × 9--19 µm.  Specialized asexual reproduction lacking.  Sexual condition autoicous.  [Seta brown to reddish brown, 2--3 cm.  Capsule light brown to reddish brown, horizontal to pendulous, sometimes nearly erect, 1--1.5 mm, ovoid to ellipsoid, contracted below the mouth when dry; operculum obliquely short-rostrate.  Spores 9--14 µm.] 


Capsules mature apparently fall (fully developed sporophytes not seen in the flora region). Low sandstone bluffs along river; altitude unreported; Miss.; Mexico; West Indies; Central America; South America. 


Isopterygium tenerifolium is known from only one recent collection from Mississippi (Lauderdale Co., E shore of Chunky R. at Stukey Bridge, ca. 32° 15' N, 88° 52' W, 30 Sept. 1992, Buck 22129 CANM, NY).  The species is morphologically close to I. tenerum, differing by the somewhat larger plants, stems often 2--4 cm, leaves 1--1.5 mm and usually wrinkled and contorted when dry, and seta 2--3 cm.  The collection in CANM contains only one plant with an undeveloped sporophyte that has a seta of 2 cm.  The species should be searched for elsewhere in the Gulf Coastal Region where other populations likely occur.