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Published In: Species Muscorum Frondosorum 104. 1801. (Sp. Musc. Frond.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 10/21/2011)
Acceptance : Accepted
Project data     (Last Modified On 10/21/2011)

37. DIDYMODON             Plates 4950.

Didymodon Hedw., Sp. Musc. 104, 1801. Lectotype: Didymodon rigidulus Hedw., fide Grout, Moss Fl. N. Amer. 1: 186, 1939.

Pottia sect. Gomphoneuron C. Müll., Linnaea 42: 310, 1879. Type: Pottia lorentzii C. Müll. (= Didymodon lorentzianus (C. Müll.) Broth. fide van der Wijk et al., Ind. Musc. 4: 540, 1967).

Pottia sect. Senophyllaria C. Müll., Linnaea 42: 311, 1879.

Sect. Didymodon

Didymodum Hedw. ex P. Beauv., Mag. Enc. 5: 309, 1804, nom. illeg. incl. gen. prior.

Didimodon P. Beauv., Mém. Soc. Linn. Paris (fasc. planch.): 3 f. 5, 1822, nom. illeg. orthogr. var.

Dydimodon Hedw. ex Arnott, Mém. Soc. Linn. Paris 5: 263, 1827, nom. illeg. orthogr. var.

Trichostomum subg. Didymodon (Hedw.) Turn., Musc. Hib. Spic. 34, 1804.

Didymodon subg. Didymodon (Hedw.) Boul., Fl. Crypt. Est Muscin. 504, 1872.

Didymodon subg. Eudidymodon Kindb., Eur. N. Amer. Bryin. 2: 273, 1897, nom. illeg.

Barbula sect. Luridae Moenk., Laubm. Eur. 281, 1927. Lectotype nov.: Didymodon rigidulus Hedw.

Barbula sect. Acutae Steere in Grout, Moss Fl. N. Amer. 1(3): 174, 1938.

Barbula sect. Didymodon (Hedw.) Giac., Atti Ist. Bot. Univ. Lab. Critt. Pavia ser. 5, 4: 208, 1947.

Barbula subsect. Acutiformes Kindb., Eur. N. Amer. Bryin. 2: 246, 1897. Type: Barbula acuta (Brid.) Brid.

Barbula subsect. Rigidulae Chen, Hedwigia 80: 193, 1941.

Sect. Asteriscium (C. Müll.) Zand., Cryptogamie, Bryol. Lichénol. 2: 383, 1981 [1982]. Type: Barbula umbrosa C. Müll.

Husnotiella Card., Rev. Bryol. 36: 71, 1909. Type: Husnotiella revoluta Card.

Trichostomopsis Card., Rev. Bryol. 36: 73, 1909. Type: Trichostomopsis crispifolia Card.

Asteriscium (C. Müll.) Hilp., Beih. Bot. Centralbl. 50(2): 618, 1933, hom. illeg. non Cham. & Schlecht., 1826.

Barbula sect. Asteriscium C. Müll., Linnaea 42: 342, 1879.

Didymodon sect. Craspedophyllon Card., Rev. Bryol. 36: 81, 1909.

Sect. Fallaces (De Not.) Zand., Phytologia 44: 209, 1979. Type: Barbula fallax Hedw.

Geheebia Schimp., Syn. ed. 2: 233, 1876. Type: Geheebia cataractarum Schimp.

Dactylhymenium Card., Rev. Bryol. 36: 72, 1909. Type: Dactylhymenium pringlei Card.

Limneria Stirt., Trans. Bot. Soc. Edinburgh 26: 428, 1915. Type: Limneria viridula Stirt.

Prionidium Hilp., Beih. Bot. Centralbl. 50(2): 640, 1933. Type: Prionidium setschwanicum (Broth.) Hilp.

Trichostomum subg. Zygotrichodon Schimp., Syn. ed. 2: 169, 1876. Type: Trichostomum tophaceum Brid.

Barbula subg. Geheebia (Schimp.) Szafr., Fl. Polska Mchy 1: 213, 1957 [1958].

Tortula sect. Fallaces De Not., Mem. Roy. Acc. Sci. Torino 40: 287, 1838. Type: Tortula fallax (Hedw.) Turn.

Barbula sect. Graciles Milde, Bryol. Siles. 117, 1869. Lectotype: Barbula rigidicaulis C. Müll. fide Saito, J. Hattori Bot. Lab. 39: 601, 1975.

Barbula sect. Pseudodidymodon Kindb., Eur. N. Amer. Bryin. 2: 246, 1897, nom. illeg. incl. sect. prior.

Barbula sect. Reflexae Mönk., Laubm. Eur. 280, 1927, nom. illeg. incl. sect. prior.

Barbula sect. Fallaces (De Not.) Steere in Grout, Moss Fl. N. Amer. 1: 174, 1938.

Didymodon sect. Graciles (Milde) Saito, J. Hattori Bot. Lab. 39: 501, 1975, see Zander, Phytologia 41: 24, 1978.

Barbula subsect. Fallaciformes Kindb., Eur. N. Amer. Bryin. 2: 246, 1897. Type: Barbula fallax Hedw.

Barbula subsect. Reflexae (Mönk.) Chen, Hedwigia 80: 203, 1941, nom. illeg. incl. sect. prior.

Sect. Rufidulus (Chen) Zand. (a comb. nov. made below).

Barbula sect. Rufidula Chen, Hedwigia 80: 210, 1941.

Sect. Vineales (Steere) Zand., Phytologia 41: 24, 1978. Lectotype nov.: Didymodon vinealis (Brid.) Zand.

Barbula sect. Vineales Steere in Grout, Moss Fl. N. Amer. 1: 174, 1938.

Barbula sect. Rubiginosae Steere in Grout, Moss Fl. N. Amer. 1: 174, 1938. Type: Barbula rubiginosa Mitt.

Barbula subsect. Vinealiformes Kindb., Eur. N. Amer. Bryin. 2: 246, 1897. Type: Barbula vinealis Brid.


            Found on a variety of substrates, mostly rock or soil; a cosmopolitan genus widely diversified in temperate and montane regions.


            Didymodon and Barbula, although often treated as one genus, are here distinguished along the lines set out by Saito (1975a) and summarized by Zander (1978e; see also treatment of Barbula). In addition, Didymodon as presented here remains an apparent potpourri of phyletic lines; Steere (1947) pointed out that Didymodon “is a synthetic genus composed of discordant elements originating in several genera of the Pottiaceae, agreeing among themselves only in their (supposedly!) [sic] untwisted peristome teeth.” Just as Barbula and Bryoerythrophyllum are closely related groups now separated as fairly homogeneous genera by a variety of characters, chief among them KOH color reactions, Didymodon, which is suspiciously heterogeneous in KOH color reactions, may prove to be profitably split by recognizing various sections as genera. Obvious candidates are described below.


Didymodon sect. Vineales

This section is characterized by the leaves spreading to widely spreading and occasionally recurved when moist, concaveacross the leaf to keeled and narrowly channeled along the adaxial surface of the costa, margins weakly decurrent to strongly so in robust plants, weakly recurved below to recurved or revolute to near the apex, often apiculate by a conical cell, the costa usually percurrent to short-excurrent in a broad mucro, the upper laminal cells occasionally bistratose along the leaf margins, epapillose to papillae simple or irregular to more often spiculose-multiplex, 1–4 over each lumen, the adaxial superficial cells of the costa quadrate in the upper half of the leaf, the guide cells occasionally in two layers, and the adaxial stereid band often absent (often replaced by substereid cells); the peristome is absent or rudimentary to well developed and twisted up to 2.5 turns; spores released usually in spring, also summer; KOH color reaction usually red to red-orange (high magnification might be needed to ascertain the exact hue of the internal upper laminal cell walls). A “marker” character, not always present but otherwise distinctive, is the absence of the quadrate ventral costal cells at the extreme leaf apex, resulting in a short, boat-shaped groove bottomed by epapillose elongate cells. Some characteristic species of sect. Vineales are D. brachyphyllus, D. cordatus, D. herzogii, D. luehmanii (Pl. 50, f. 8–11), D. luridus, D. nicholsonii, D. occidentalis, D. reedii, D. sinuosus, D. tectorum and D. vinealis.


Didymodon sect. Fallaces

This section is distinguished by the leaves spreading to often strongly recurved when moist, concave to keeled, margins weakly to strongly decurrent, plane to recurved in lower 2/3, not apiculate, the costa ending below the apex to short-excurrent, the upper laminal cells unistratose, epapillose to papillae simple, hemispherical or occasionally conic-apiculate, usually 1–2 over each lumen, the adaxial superficial cells of the costa short-rectangular to elongate in the upper half of the leaf (except D. asperifolius) and the adaxial stereid band usually present; peristome rudimentary to well developed and twisted up to 2 turns; spores mature usually in winter or spring; KOH color reaction usually reddish orange. The correct name at the generic level would be Geheebia. This section is morphologically similar to Hymenostylium by the commonly exposed ventral stereid band and often angular upper medial cell lumens.

            Although Sollman (1983) has synonymized D. constrictus with D. (sect. Vineales) vinealis, the type of the former at NY (“170”) is a mixed collection but largely composed of plants identical with other NY specimens (“Walanchoon” and “Lachen”) labeled in Mitten's hand as “Barbula constricta.”  These are not D. vinealis but have clearly elongate ventral cells; the Asian D. constrictus is near to or the same as the dark-red colored D. (sect. Fallaces) laevigatus of the Andes. Specimens identified in various herbaria as D. constrictus but with quadrate ventral costal cells are usually D. (sect. Didymdon) rigidulus var. icmadophilus, which has a similar very short leaf base filled with quadrate cells and a very long-acuminate upper leaf.

            Although Syed and Crundwell (1973) indicated that Didymodon maxima (as Barbula maxima) lacked a central strand, it usually has one, albeit weakly developed, even in European plants (e.g. Ireland: Crundwell & Warburg 1962, NY). Trigones, similar to those of Didymodon giganteus, are present in the leaves of most specimens. Hill (1981) and H. Crum and D. Hall (in press) have pointed out that Didymodon ferrugineus (Schimp. ex Besch.) Hill is the correct name for D. fallax var. reflexus at the species level. Some characteristic species of sect. Fallaces are D. asperifolius, D. calycinus (Pl. 50, f. 1–3), D. ceratodonteus (Pl. 50, f. 4–7), D. constrictus, D. fallax, D. ferrugineus, D. erosodenticulatus, D. giganteus, D. hastatus, D. inundatus, D. johansenii, D. laevigatus, D. maxima, D.  michiganensis, D. nigrescens, D. spadiceus (Pl. 50, f. 12–16), D. tomaculosus (differs from D. fallax only in the presence of rhizoidal propagula), D. tophaceus and D. waymouthii (Pl. 50, f. 17–21).


Didymodon sect. Asteriscium

This section is characterized by the stem occasionally with a hyalodermis, leaves spreading to spreading-recurved when moist, occasionally squarrose from a shortly sheathing base, broadly channeled, leaf margins not decurrent, plane to broadly recurved throughout, the costa ending 1–6 cells below apex to short-excurrent, often rather broad at midleaf, adaxial surface convex, upper laminal cells unistratose to bistratose evenly or in patches along the leaf margins, papillae absent to large, low, simple to bifid 1(–4) per cell lumen, adaxial superficial cells of costa quadrate to elongate, adaxial stereid band absent or very small, hydroid groups often present; KOH color reaction usually yellow or yellowish orange. If recognized at the genus level, the correct name would be Husnotiella or Trichostomopsis, both published at the same time. This section represents at least superficially a morphological intermediate, as noted by Hilpert (1933), between Didymodon and Erythrophyllopsis in that the upper lamina of D. challaense is bistratose in patches medially or completely. Some characteristic species are D. australasiae, D. bartramii (Pl. 49, f. 24–26), D. challaense, D. revolutus and D. umbrosus. Probably also belonging here is D. marginatum.


Hydroid strands are of scattered occurrence in the genus Didymodon, having been seen in D. australasiae, D. ceratodonteus, D. luehmanii, D. revolutus and D. xanthocarpus. This feature is evidently of little taxonomic utility at the present time.

            Didymodon tophaceus, a relatively common species of wet habitats, may lack a peristome in some specimens, which occasionally appear as taxonomic types of certain synonyms (e.g. Gymnostomum knightii Schimp. in Knight, BM) originally described as members of other, characteristically eperistomate genera.

            The type of Didymodon occidentalis (NY) lacks a peristome entirely (it is not retained in the operculum on dehiscence). The sect. Vineales is similar to Bryoerythrophyllum in red coloration in KOH but is distinguishable from the latter by the usually sharply acute leaves, smaller upper laminal papillae, and often more than one layer of guide cells in the costa, which also often lacks a ventral stereid band.

            Didymodon lindigii of the Andes has bistratose upper margins and apex, and rudimentary peristome, and is apparently close to Didymodon rigidulus (Pl. 49, f. 1–14). The several apparent isotypes at NY consist of considerable admixture with D. tophaceus and D. australasiae, while the isotype at FH is solely of the last two; lectotypification is sorely needed, with attention to possible confusion with Astomum lindigii (cf. Mitten's 1859 treatment of this last species).

            Weissia waymouthii (Pl. 50, f. 17–21) is here transferred to Didymodon (sect. Fallaces) reflecting its recurved lower leaf margins, elongate ventral cells of costa, lack of a differentiated ventral costal epidermis, upper laminal cells pellucid, thick-walled, with rounded lumens and medially longitudinally elongate, and papillae low and simple. The absence of a central strand in D. waymouthii is unusual in the genus, and might indicate a relationship with Hymenostylium, but the species is retained at least tentatively in Didymodon because of the presence of a peristome and costa ending a few cells below the apex. The KOH color reaction is reddish orange, not the characteristic yellow of Weissia species.

Literature: Abramova et al. (1987), Allen (1992), Andrews (1941), Bartram (1926a,c), Conard (1945a, 1951a), Corley et al (1987), Crum (1965b, 1969a), Crundwell (1976), Crundwell and Nyholm (1965), Crundwell and Whitehouse (1978), Dismier (1905), Düll (1984), Düll-Hermanns (1984), Düll-Hermanns and Düll (1985), Eckel (1986a), Ellis and Smith (1983), Guerra and Ros (1987), Herzog (1905), Hill (1978), Hillier (1931), Lal and Parihar (1980), Matteri (1988a), Mitten (1867), Philibert (1885), Preston and Whitehouse (1985), Robinson (1968, 1970), Savicz-Ljubitzkaja (1965b), Sollman (1983), Steere (1938b), Vashistha and Chopra (1984), Werner (1982), Williams (1913), Zander (1978b,h, 1981c), Zander and Delgadillo (1984).
Number of accepted species: 122
Species Examined: D. alticaulis (DUKE, TENN), D. amblyophyllus (NY), D. anserinocapitatus (NY), D. asperifolius, D. australasiae, D. bartramii (F, US), D. brachyphyllus (BUF), D. calycinus (BM, NY), D. cardotii, D. ceratodonteus (NY, PC), D. challaense (H), D. constrictus (BUF, NY), D. cordatus (BUF, F), D. crassicostatus (FH), D. deciduus (NY), D. fallax, D. ferrugineus, D. giganteus, D. herzogii (JE, L), D. hampei (BM, BUF, FH, TENN), D. hastatus (NY), D. humidus (NY), D. imperfectus (H), D. incrassatolimbatus (BM, FH, NY, TENN), D. inundatus (NY), D. japonicus (H), D. johansenii (ALA, MICH), D. laevigatus (BUF, NY), D. lamyanus (F), D. leskeoides (ALTA, BUF, NY, UBC), D. lindigii (NY), D. lingulatus (NY, BM), D. luehmanii (BUF), D.luridus, D. jackvancei (NY), D. marginatum (NY), D. maxima (NY), D. michiganensis (DUKE, NY, TENN), D. minusculus (NY), D. nicholsonii (BUF, HSC, UBC, US), D. nigrescens (COLO, DUKE, FH, NY, US), D. occidentalis (NY), D. patagonicus (NY), D. perobtusus (H, NY), D. pruinosus (NY, BUF), D. reedii (US), D. revolutus, D. rigidulus, D. rivicola (BUF), D. rufidulus (BUF), D. sinuosus (BUF, NY), D. spadiceus, D. stewartii (NY), D. subandreaeoides (ALA, CANM, NY), D. subtorquatus (US), D. taylori (NY), D. tectorum (H), D. tomaculosus (BUF), D. tophaceopsis (BUF, NY, US), D. tophaceus, D. torquatus (HSC), D. umbrosus, D. uruguayensis (US), D. vinealis, D. waymouthii (NY), D. xanthocarpus (NY).


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Plants gregarious or more usually forming turfs or cushions, light to blackish, olive or reddish green above, brown to reddish brown or tan below. Stems branching seldom to often, to 2(–9) cm in length, transverse section rounded-pentagonal, occasionally rounded-triangular, central strand usually distinct, seldom absent, sclerodermis usually present, hyalodermis only occasionally present; axillary hairs of ca. 5 cells, basal 1–2 cells brownish; indumentum usually absent. Leaves often crowded, appressed-incurved and occasionally twisted or curled when dry, spreading when moist, ovate or more usually lanceolate or long-lanceolate to occasionally long-triangular, ca. 0.8–3.0(–6.0) mm in length, upper lamina usually broadly concave, occasionally narrowly channeled or keeled, margins seldom plane or more usually recurved or occasionally revolute, entire or occasionally weakly dentate or crenulate, occasionally bistratose in patches or entirely so; apex narrowly acute to rounded, seldom cucullate; base weakly differentiated to ovate, occasionally oblong and half-sheathing the stem, occasionally decurrent, shoulders rarely present; costa ending several cells below apex to excurrent as a blunt awn, superficial cells quadrate to elongate ventrally, usually short-rectangular dorsally above midleaf, smooth or occasionally papillose, 2–4(–8) rows of cells across costa ventrally at midleaf, costal transverse section ovate, semicircular or reniform, stereid bands usually weak, occasionally absent ventrally, ventral epidermis present or seldom absent, dorsal present but usually weak, guide cells 2–6(–8) in 1(–2) layers, hydroid strand seldom present; upper laminal cells subquadrate to hexagonal or rounded angular, occasionally short-rectangular or rhomboidal, usually 8–13 µm in width, 1:1, occasionally bistratose in patches or entirely, walls thin to thickened, lumens sometimes angular, occasionally trigonous, superficially weakly to strongly convex on both surfaces; papillae usually low, simple to bifid, usually solid, not obscuring the lumens, occasionally absent or multiplex; basal cells usually weakly differentiated to occasionally strongly differentiated across leaf or extending higher medially, occasionally little different from upper cells, quadrate to rectangular, seldom bulging, usually little wider than the upper, ca. 2–4:1, walls usually rather thin, occasionally porose, smooth to papillose. Propagula occasionally present, green, usually comparatively small, spherical to elliptical, of 1–10 cells, usually borne in leaf axils, occasionally on ventral surface of costa or on basal rhizoids; occasionally the leaf apex swollen and fragile. Dioicous (occasionally possibly rhizautoicous). Perichaetia terminal, inner leaves ovate to long-lanceolate, occasionally enlarged, not or occasionally sheathing in lower 1/2, seldom convolute-sheathing, lower cells rhomboidal-rectangular in lower 1/2. Perigonia terminal or occasionally as small buds on protonema near archegoniophore. Seta mostly 0.5–2.0 cm in length, 1(–2) per perichaetium, yellowish to reddish brown, twisted clockwise below, occasionally counterclockwise above; theca ca. 1–3 mm in length, yellowish to reddish brown, elliptical to cylindrical, exothecial cells rectangular, thin-walled, stomates phaneropore, at base of theca, annulus of 1–3 rows of hexagonal, often vesiculose cells, often deciduous in pieces or revoluble; peristome teeth 16, or 32 and grouped in pairs, occasionally rudimentary or rarely absent, oblong to linear or long-triangular, often perforate or cleft medially, papillose to spiculose or spirally striate, to 700(–1300) µm, often of many articulations, usually straight or weakly twisted counterclockwise, but sometimes strongly twisted, basal membrane absent or low, occasionally to 70 µm in height, papillose or spiculose. Operculum short- to long-conic or conic-rostrate, ca. 0.5–1.2 mm in length, cells in straight rows or weakly twisted counterclockwise, occasionally to twice twisted. Calyptra cucullate, smooth, ca. 2.0–2.5 mm in length. Spores ca. 7–15 µm in diameter, light brown, smooth to papillose. Laminal KOH color reaction yellow or red. Reported chromosome number n = 12, 12+m, 13, 14.
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