BFNA Title: Orthodontiaceae
Author: P. M. Eckel
Date: July 21, 2011
Edit Level: R
Version: 1b

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden
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Patricia M. Eckel



Plants small, in loose tufts or scattered individuals, acrocarpous, pseudo-pleurocarpous (reproductive structures on lateral innovations). Stems 10--17 mm, erect, in section with or without a central strand, epidermis not differentiated. Leaves erect-spreading, lanceolate, linear-lanceolate to setaceous from an undifferentiated base, narrowed at the insertion; costa 1/3--1/5\x the leaf width, ending before the apex to percurrent, in section undifferentiated or with a central stereid band; margins 1-stratose, entire but denticulate in the apex; laminal cells linear, smooth, with firm walls, becoming larger, lax, thin-walled, short-rectangular to subquadrate near the insertion, cells at insertion red-brown in one or two rows. Specialized asexual reproduction frequent, by filamentous, 1-seriate, reddish brown propagula in the axils of the leaves. Sexual condition autoicous or paroicous, archegonia scattered distally on the stem, antheridia naked among the perichaetial leaves or in lateral stalked perigonial buds below the perichaetia, or both, leaves acute, ovate-lanceolate, ca. 1/5\x cauline leaf length or less; perichaetial leaves scarcely differentiated. Seta elongate, greatly exceeding capsule length. Capsule erect, ovoid to subcylindric to oblong-pyriform, irregularly longitudinally wrinkled to somewhat furrowed when dry, tapering to a neck up to 1/3\x capsule length; exothecial cells evenly thin-walled, long- to short-rectangular; annulus absent or rudimentary, persistent  in 2--3 rows, adherent to the capsule mouth after dehiscence; operculum conic, obliquely short- to long-rostrate; peristome diplolepideous-alternate, of 16 teeth; exostome pale yellow-brown, inserted somewhat below the capsule mouth, narrowly lanceolate from a somewhat broader to broader base, scarcely trabeculate, smooth or finely papillose, median fissural line present; endostome segments undivided, hyaline to pale yellow, smooth to finely papillose, somewhat reduced, as long as to shorter than the exostome, with or lacking the median line,  endostomial basal membrane short or absent, endostome smooth or lightly papillose; cilia absent. Calyptra fugacious, cucullate, smooth, naked. Spores (11--)16--18(--20) \um, spherical, densely and finely to coarsely papillose.


Genera 4 (1 in the flora): tropical-temperate worldwide.


The placement of the Orthodontiaceae is currently undergoing rapid revision. Goffinet et al. (2008) placed the family in the order Rhizogoniales together with the Rhizogoniaceae and Aulacomniaceae. This is quite different and distant from the order Bryales with which the family has traditionally been associated. W. Frey (2009) more recently recognized the family in the order Orthodontiales, and segregated the other two families to their own orders, Aulacomniales and Rhizogoniales. Orthodontium was elevated to family status by W. R. Buck and B. Goffinet (2000). The genus was, however, retained within the family Bryaceae by B. H. Allen (2002) who adopted a broader generic view of that large and complex family. The Orthodontiaceae is widespread in tropical and temperate regions, primarily epiphytic on coniferous trees, decaying coniferous wood, or in terrestrial habitats. Buck and Goffinet (2000) characterized the Orthodontiaceae as having no annulus; Allen (2002) pointed out that the genus Orthodontium in fact did possess an annulus. 


SELECTED REFERENCES  Allen, B. H. 2002. Moss Flora of Central America. Part 2. Encalyptaceae--Orthotrichaceae. St. Louis. Buck, W. R. and B. Goffinet. 2000. Morphology and classification of mosses. In: A. J. Shaw and B. Goffinet, eds. 2000. Bryophyte Biology. Cambridge: Pp. 71--123. Frey, W., ed. 2009. Syllabus of Plant Families, Adolf Engler’s Syllabus der Pflanzenfamilien. Part 3. Bryophytes and Seedless Vascular Plants. ed 13. Stuttgart, Germany.  Goffinet, B., W. R. Buck and A. J. Shaw. 2008. Morphology, anatomy and classification of the Bryophyta. In: Bryophyte Biology, Second Edition. B. Goffinet and A. J. Shaw, eds. Cambridge, pp.55--138.


1. ORTHODONTIUM Schwägrichen, Sp. Musc. Frond., Suppl. 2 2((2)): 123. 1827  *  [Greek, orth-, erect, and odont-, tooth, and Greek diminutive -ium, alluding to straight or erect peristome teeth]


Plants densely foliose, shiny or glossy,  light yellow-green to yellow-brown. Stems to 2 cm but usually shorter, simple or forked at the base, moderately radiculose from stem and leaf bases, radicles hyaline to reddish, smooth, with oblique tangential walls, central cylinder relatively small. Leaves patent, dense at the base and crowded at stem apex, leaves erect-spreading when dry, spreading when moist, keeled or shallowly carinate with recurved or erect laminae, one or both laminae plane to undulate-sinuolate, apex slenderly acute; margins plane or partly broadly recurved, smooth, slightly denticulate in the apex; laminal cells apically short- to long-rectangular median laminal cells long and narrow, linear to linear-rhomboidal,  firm-walled distally, broader, thin-walled and laxly oblong-hexagonal proximally; 1--2 rows of cells at insertion red-brown, equilateral to short-rectangular, somewhat thicker than the larger and more lax cells just distal; costa usually ending subapically, less often shortly excurrent, with or without stereid bands. Perichaetial leaves scarcely differentiated. Seta slender, erect-flexuose, yellowish. Capsule symmetric, smooth when wet; exothecial cells pale brown to yellow-brown; stomata phaneropore, located in the capsule neck; operculum obliquely rostrate; stomata phaneropore, located in the capsule neck.


Species 14 (2 in the flora): worldwide in tropical and temperate regions.


Orthodontium was monographed by W. Meijer (1951), and both species were treated in Mexico by Crum (1994). Both species in the flora area may grow on the rotten wood of coniferous trees, in the West, particularly Sequoia sempervirens. The leaves are narrowed at the base and have 1--2(--4) rows of brown cells at the leaf insertion, which appear to be associated with rhizoid initials. Both species bear filamentous propagula from the rhizoids (J. G. Duckett et al. 2001). A. E. Newton and N. E. Bell (2007), during an analysis of Orthodontium lineare, indicated that the stem of Orthodontium may produce branch-axes “by a method other than branch primordia,” that is, from stem epidermal cells, including perichaetial and perigonial as well as vegetative branch-axes. These branch-axes are loosely attached to the parent stem by short rhizoids, and may produce innovations by small clusters of cells, one of which “will differentiate into an apical cell and produce a short branch,” according to them a possible homology with the mechanism of rhizautoicy. The Orthodontium peristome is double, but with the endostome variously reduced and with a low basal membrane and cilia are wanting. The linear-setaceous leaves are superficially similar to those of some genera in the Bryaceae, but that family generally has rather broader leaves and more rectangular to quadrate laminal cells (longer than 4:1).


The common Leptobryum pyriforme (Meessiaceae) also has setaceous leaves, but the setaceous portion is distal to an abruptly flaring base, the leaves are distant in the proximal part of the stem but densely foliate distally, whereas in Orthodontium the leaves are entirely setaceous and narrowed to the insertion, and dense to the stem base. Leptobryum has a horizontal or pendent pyriform capsule (not erect to suberect) which is glossy (not dull or matte) brown. It also has a perfect peristome including appendiculate cilia, but Orthodontium species have an endostome with a narrow basal membrane with no cilia.  Gametophytically Orthodontium may resemble species of Dicranaceae in the reddened and lax cells at the laminal insertion, but it differs in the smooth, evenly long-rectangular to linear cells, subserrulate apex, and narrow costa (see discussions of D. H. Norris and J. R. Shevock 2004a, 2004b).


In the western United States, the genus is “apparently restricted to the perhumid forests near the Pacific Coast, generally among the coastal Sequoia” (D. H. Norris and J. R. Shevock 2004a). The range of both species overlap in California. The two species in the flora “doubtless represent a relict from the Tertiary flora (Andrews 1932).  Comments (M. S. Ignatov et al. 2006) regarding the related genus Orthodontopsis, found in pristine coniferous mountain forests of Mongolia and Russia, perhaps apply to species of Orthodontium in the floral area, that is, the evergreen substrates and associated flora provide the ideal habitat for Orthodontium due to the slow rate of the decay of coniferous wood. Populations of Orthodontium species in pristine areas in the floral area may be particularly vulnerable to habitat disturbance from logging. Five species in the genus are reported to occur in the New World in South America, but only Orthodontium gracile and O. pellucens are widespread there, extending north into the flora area (C. Delgadillo M. et al. 1995).


SELECTED REFERENCES  Andrews, A. Le Roy. 1932. The California Stablerias. Bryologist 35: 49--51. Crum, Howard. 1994. Orthodontium In: A. J. Sharp, H. A. Crum and  P. M. Eckel, eds. 1994. Moss Flora of Mexico. Memoirs of the New York Botanical Garden  69: 520--521.   Delgadillo M., C., B. Bello and A. Cardenas S. 1995. Latmoss, a Catalogue of Neotropical Mosses. Monographs in Systematic Botany from the Missouri Botanical Garden 56.  Duckett, J. G., J. A. Goode and H. W. Matcham. 2001. Studies of protonemal morphogenesis in mosses. VIII. The gemmiferous protonemata of Orthodontium and Dicranoweisia. J. Bryol. 23: 181--193.  Ignatov, M. S., Ignatova, E. A., Tsegmed, T. and B. C. Tan. 2006. The genus Orthodontopsis Ignatov & B. C. Tan (Bryaceae, Bryophyta) in Russia, Mongolia and China. Arctoa  15: 163--168.  Meijer, W. 1951. The genus Orthodontium. Acta Bot. Neerl. 1:1--80.  Newton, A. E. and N. E. Bell. 2007. Pleurocarpy in the Rhizogoniaceous Grade. In A. E. Newton and R. S. Tangney, eds. 2007. Pleurocarpous Mosses: Systematics and Evolution. London, pp. 41--64.  Norris, D. H. and J. R. Shevock. 2004a. Contributions toward a bryoflora of California: I. A specimen-based catalogue of mosses. Madroño 51: 1--131. Norris, D. H. and J. R. Shevock. 2004b. Contributions toward a bryoflora of California: II. A key to the mosses. Madroño 51: 133--269.


1. Leaves narrowly setaceous, 0.1--0.2 mm wide at midleaf; distally flexuose wet or dry; costa in cross section without stereid cells; paroicous or polygamous, antheridia found among the perichaetial leaves or in buds below the perichaetium; capsule subcylindric, exostome teeth smooth, basal membrane of endostome none; endostome segments shorter than the teeth; operculum conic and/or short- and obliquely rostrate .................1. Orthodontium gracile


1. Leaves broadly linear, 0.5 mm wide at midleaf; 1\x twisted along the leaf length wet or dry; costa in cross section with stereid cells; autoicous, antheridia found only in buds below the perichaetium; capsule ovoid-pyriform (wider at or just above the middle); exostome teeth finely papillose; basal membrane low; endostome segments about as long as the teeth; operculum conic and long- and obliquely rostrate ................. 2. Orthodontium pellucens



1. Orthodontium gracile (Wilson in Smith) Schwägrichen ex Bruch, Schimper & W. Gümbel, Bryol. Eur. 4: 70 (fasc. 23--24. Mon. 4). 1844  F


Bryum gracile Engl. Bot., 2835. 1838


Plants mostly 5--20(--30) mm, glossy-vitreous. Stems without a central strand. Leaves (1--)2--3(--4.5) mm, 0.1--0.2 mm wide at midleaf, widest below the middle, narrowly setaceous, margins broadly recurved; distally strongly flexuose wet or dry; costa in cross section without stereid cells. Sexual condition paroicous or polygamous, antheridia found among the perichaetial leaves below the archegonia or in buds below the perichaetium. Seta 4--5(--9) mm. Capsule (1--)1.5--2 mm, subcylindric, neck nearly as long as or to 1/3 the length of the capsule; exostome teeth smooth, somewhat wider at the base, basal membrane of endostome none; endostome segments shorter than the teeth; operculum conic and short- and obliquely rostrate.


Capsules mature winter to early spring. Moist creek ravines and canyons, bases of cliffs, riparian forests of Alnus, Acer, Lithocarpus, Pseudotsuga, Sequoia, shaded decayed or charred logs and stumps, bark base of trees, epiphytic on Sequoia sempervirens, peaty soil or soil over rock;  moderate elevations; Calif., Oreg.; disjunct to southwestern Mexico; West Indies; Central America; South America; w Europe; Africa.


W. Meijer (1951) depicted both the smooth exostome of O. gracile and the papillose one of O. pellucens with a median fissural line. The endostome of both species was drawn with the fissural line absent except at the base. As described and drawn by Meijer, the lengths of the endostomes of both species seem to be the same. Recent treatments of these characters diverge from Meijer and present contradictions. The papillosity of the O. pellucens exo- and endostome may be variable throughout its range. B. H. Allen (2002), for example, observed that in Central America both of these structures were without papillae. Further study is required to clarify these characters.


2. Orthodontium pellucens (Hooker) Bruch, Schimper & W. Gümbel, Syn. Musc. Frond. 1: 240. 1848  F


Bryum pellucens Hooker, Icon. Pl. 1: plate 34. 1836


Plants mostly 5--10 mm, shiny-opaque. Stems with or without a central strand. Leaves 2.5--5 mm, 0.5 mm wide at midleaf, widest at the middle,  broadly linear, keeled, margins erect; 1\x twisted along the leaf length wet or dry; costa in cross section with stereid cells. Sexual condition autoicous, antheridia found only in stalked buds which are numerous along the stem to well below the perichaetium. Seta 7--14 mm. Capsule 1.5--1.7 mm, ovoid-pyriform (wider at or just above the middle); with a rather short neck, exostome teeth finely papillose, not much wider at the base; basal membrane present but low; endostome segments about as long as the teeth;  operculum conic and long- and obliquely rostrate.


Capsules mature winter to early spring. In the East in peaty crevices of rock, treeless heath balds of dense evergreen shrubs: Rhododendron katawbensis, Kalmia latifolia, Gaylussacia baccata on mountain summits, shaded rotten wood, bark of tree bases, pine logs and stumps, peaty humus, soil, thin soil over calcareous rock, in the West in moist creek ravines and canyons in moist forests of Pseudotsuga, Lithocarpus, Sequoia sempervirens, Vaccinium ovatum,  Polystichum muticum, Morella californica, Acer macrophyllum; low to high elevations 100--1500 m); Calif., Oreg., N.C., Tenn.; disjunct to south central and south eastern Mexico; West Indies; Central America; South America; Pacific Islands (Galapagos Islands, Hawaii).


B. H. Allen (2002) in his extensive treatment of these two species for Central America, pointed out and illustrated the stem central strand of O. pellucens. The occurrence of this character is variable in sections made from a single stem. The cells of the central cylinder generally appear to be smaller than the epidermal cells and with diligence, a central cluster of 3--4 significantly even smaller cells may be demonstrated. The central cylinder of O. gracilis appear to be larger than the epidermal cells and no central strand is evident.


Orthodontium pellucens is a species with perhaps the widest leaves in the genus in the median part of the leaf, to 0.5 mm (W. Meijer 1951), wider than that of O. gracile, to 0.2 mm. The distal portion of the leaf is more broadly acute and not flexuose-sinuose as in O. gracilis. The length of the rostrum is usually 0.75--0.8 mm, that is, to 1/3 the length of the capsule (W. Meijer 1951). Capsules are not known for the mountainous southeastern United States of which only three specimens were reported by H. A. Crum and L. E. Anderson (1981). ). According to A. L. Andrews (1932) the species of Orthodontium in California “normally fruit well.” No California fruiting material was seen.


Orthodontium lineare Schwägrichen is a species of Europe and the southern hemisphere in South Africa, New Zealand and Australia (W. Meijer 1951). It is considered a weedy introduction in Britain from which stations the species is spreading eastward in continental Europe, perhaps even threatening the viability of O. gracile in Britain (A. J. E. Smith 2004). The species perhaps might be expected to occur in the flora area at some future time. Like O. pellucens it has stereids in the costa but its leaves are matt (not glossy), are distally quite entire (not somewhat denticulate in the apex) and the operculum is short rostrate to conic (not long-rostrate).


OTHER REFERENCES  Crum, H. A. & L. E. Anderson. 1981. Mosses of Eastern North America. Columbia University Press. Vol. 1. Smith, A. J. E. 2004. The Moss Flora of Britain and Ireland, ed.2. Cambridge.