BFNA Title: Leptodictyum
Author: S. G. Newmaster 
Date: April 18, 2008
Edit Level: R 
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden

BFNA Web site:


Return to Home


LEPTODICTYUM - Amblystegiaceae


XXX.  LEPTODICTYUM (Schimper) Warnstorf, Kryptogamenfl. Brandenb., Laubm., 867. 1906 * [Greek lepto, thin or fine, alluding to the fine outline of the leaf cells]


                                                                                                                    S. G. Newmaster

Amblystegium subgen Leptodictyum Schimper, Syn. Musc. Eur., 595. 1860


Plants medium-sized, green, yellow-green, brown-green, in thin, loose to dense mats.  Stems prostrate, irregularly to subpinnately branched, without a hyalodermis; epidermal cells small and thick-walled; pseudoparaphyllia foliose, lanceolate; rhizoids or rhizoid initials on stem or at abaxial leaf costa insertion, smooth, slightly branched.  Stem and branch leaves similar, erect-spreading, not secund, somewhat complanate, oblong-lanceolate, acute or acuminate, not plicate, nondecurrent; marginal lamina cells 1-stratose, margins plane, entire or serrulate; costa single, ending in distal half before the apex; median lamina cells linear, smooth, thin- to thick-walled; alar cells enlarged, rectangular, thin walled, not extending up the leaf, not decurrent.  Specialized asexual reproduction lacking.  Sexual condition autoicous.  Perichaetial leaves lanceolate, acuminate, erect, margin entire; lamina cells smooth.  Seta single, elongate, smooth.  Capsule cylindrical, inclined to horizontal, curved, contracted below mouth; annulus of 2--3 rows of large, deciduous cells; operculum conic, apiculate; peristome perfect, yellow to brown; endostome hyaline, filiform, cilia 1--4, nodulose.  Calyptra cucullate, naked.  Spores globose to ovoid, yellow to yellow-brown, minutely papillose, 10--15 \um.


Species 7 (2 in flora): circumtemperate.


L. Hedenäs (2003) included in this genus only a single, variable species, Leptodictyum riparium, with L. humile treated in Amblystegium. According to A. Vanderpoorten et al. (2001, 2002), L. humile should be treated as a member of Hygroamblystegium. From a morphological point of view, there is in fact a continuum between Hygroamblystegium humile and H. tenax, the only actual feature distinguishing the two being the length of the costa, which continuously varies from ceasing at mid-leaf to percurrent. The most recent molecular analyses (A. Vanderpoorten, personal commmunication) suggest that Leptodictyum riparium falls within a completely unrelated clade together with large Campylium species. A. Vanderpoorten et al. (2002) suggested that Leptodictyum riparium appears more closely related to Campylium stellatum and Campyliadelphus chrysophyllus than to Amblystegium species. Further molecular evidence is needed to resolve these systematic issues.


SELECTED REFERENCE:  Conard, H. S. 1959. Amblystegium. Bryologist 62: 96--104. Allen, B. and R. E. Magill. 2004. Leptodictyum wallacei (Musci: Amblystegiaceae), a new species from Texas, U.S.A.  Novon 14: 377--379. Hedenäs, L. 2003. Amblystegiaceae (Musci). Flora Neotropica, Monograph 89: 1--107. Vanderpoorten, A., A. J. Shaw, and B. Goffinet. 2001. Testing controversial alignments in Amblystegium and related genera. (Amblystegiaceae: Bryopsida). Evidence from rDNA ITS Sequences.

Syst. Bot. 26: 470--479. Vanderpoorten, A., L. Hedenäs, C. J. Cox,  and A. J. Shaw. 2002. Circumscription, classification, and taxonomy of Amblystegiaceae (Bryopsida) inferred from nuclear and chloroplast DNA sequence data and morphology. 51: 115--122.


1.  Plants flaccid, large, 6--20 cm; leaf basal cell walls lax, alar cells differentiated...……………………….….. 1. Leptodictyum riparium

1.  Plants stiff, smaller, 3--6 cm; leaf basal cells firm-walled, alar cells not differentiated…………………..………… 2. Leptodictyum wallacei



1.  Leptodictyum riparium (Hedwig) Warnstorf, Kryptogamenfl. Brandenb., Laubm., 878. 1906


Hypnum riparium Hedwig, Sp. Musc. Frond., 241. 1801; Amblystegium brevipes Cardot & Thériot in Holzinger; A. riparium var. flaccidum (Lesquereux & T. P. James) Renauld & Cardot; A. riparium var. fluitans (Lesquereux & T. P. James) Renauld & Cardot in Macoun; A. riparium var. longifolium (Schultz) W. P. Schimper in M. Lange; Amblystegium riparium (Hedwig) Schimper in B.S.G.; Brachythecium pennellii E. B. Bartram; Campylium polygamum var. longinerve (Renauld & Cardot) Grout; Leptodictyum brevipes (Cardot & Thériot in Holzinger) Brotherus; L. riparium var. abbreviatum (Schimper in B.S.G.) Grout; L. riparium var. brachyphyllum (Cardot & Thériot in Holzinger) Grout; L. riparium var. elongatum (Schimper in B.S.G.) Warnstorf; L. riparium var. flaccidum (Lesquereux & T. P. James) Grout; L. laxirete (Cardot & Thériot) Brotherus; L. sipho (Palisot de Beauvois) Brotherus; L. vacillans (Sullivant) Brotherus; Rhynchostegiella georgiana Dixon & Grout


Stems irregularly branched, in flat, loose, flaccid, long trailing mats, light green to yellow-brown, 6--20 cm, branches spreading.  Leaves 2.5--6 mm, slightly contorted when dry, erect to wide spreading or appearing distichous, somewhat complanate especially in branches, distant, often obliquely attached to stem, broadly short to gradually long acuminate, costa (45)52.5--114 \um at base, margins entire, upper cells long, rhomboidal, (34--)42--117 x 7.5--12(--13) \um, basal cell walls lax, alar cells differentiated, enlarged, rectangular.  Seta 8--26 mm, light to dark brown.  Capsule 2.2--2.5 mm long, cylindric, arcuate, brown to reddish brown.  Spores finely papillose, 10.5--18.5 \um.


Capsules rare. Humus, logs and tree bases in swamps or wet depressions in forests or aquatic on rocks in streams and rivers; low to moderate elevations; Greenland; Alta., B.C., Man., N.B., Nfld. and Labrador, N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., Fla., Ga., Ill., Ind., Iowa, Kans., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; Central America; South America; Europe; Asia; Africa; Indian Ocean Islands; Pacific Islands; Australia.


As the specific epithet implies, Leptodictyum riparium occurs along rivers, often in flooded areas where it is stranded on tree bases in hardwood forests. It is sometimes confused with another wetland species, Drepanocladus aduncus, which differs in axillary hairs with 1--3 distal hyaline cells. There is tremendous morphological variability among the North American specimens of Leptodictyum riparium, suggesting the existence of several ecotypes, which have been erroneously named as many varieties and forms in Leptodictyum, Amblystegium, and Campylium. These synonyms are summarized by A. J. Grout (1928--1934), H. S. Conrad (1959), and H. A. Crum and L. E. Anderson (1981).   



2.  Leptodictyum wallacei B.H. Allen & Magill, Novon 14: 377, fig. 1. 2004


Stems sparingly branched, in slender, stiff strands, green to yellow-brown, 3--6 cm, branches spreading.  Leaves 2--2.5 mm, erect to wide spreading, strongly contorted when dry, often transversely attached to the stem, gradually long-acuminate; costa 50--75 \um at base; leaf margins entire or obscurely serrulate; distal laminal cells long, rhomboidal, 70--120 x 6--7 \um, basal cells firm walled, alar cells not differentiated.  Sporophytes not seen.


Large submerged masses, endemic to Hext Spring, San Saba Co., Texas.


There appears to be enough morphological evidence to support the recognition of Leptodictyum wallacei, which is distinguished from the variable aquatic ecotypes of Leptodictyum riparium by its stiff stem, smaller size and absence of alar cell elaboration. However, Lars Hedenäs (personal communication) has examined an isotype and suggested that the specimen fits well within the variation of Leptodictyum riparium. Further molecular evidence is needed to evaluate the haplotype variation of L. riparium.