BFNA Title: Leucodon
XX. LEUCODON Schwägrichen, Spec. Musc. Suppl. 1(2): 1. 1816 * [Greek leuco, white, and odont, a tooth, alluding to the pale peristome teeth]
William D. Reese
Plants medium-size to robust, glossy or dull, with creeping primary stems bearing erect to spreading, (rarely pendent) branches, green to brownish green. Stems irregularly branched, axillary hairs 3--5 per leaf axil, of 2 short proximal cells with brownish walls and 2--3 longer distal cells. Stem leaves imbricate, small, abruptly or gradually slenderly acuminate, with straight or falcate sometimes filiform apices, margins entire, costa lacking; medial cells smooth, oblong-rhomboidal to linear, thick-walled, often porose, alar cells quadrate in large areas. Branches short to elongate, straight or curved, mostly simple, terete. Branch leaves larger than stem leaves, imbricate, concave, erect-appressed when dry, ascending to spreading when wet, ovate-lanceolate to acuminate, somewhat concave, smooth or plicate, cells similar to those of stem leaves, margins plane to reflexed, entire, or serrulate distally, apices acute. Specialized asexual reproduction lacking or by small slender caducous axillary branchlets. Sexual condition dioicous; perichaetia on short lateral branches, leaves strongly differentiated, greatly elongate, sheathing base of seta; perigonia gemmiform, axillary. Seta short to elongate. Capsule erect, immersed to exserted, ovoid to pyriform; annulus of several rows of differentiated cells; operculum conic or obliquely rostrate, gripped apically by the calyptra and lifted to open the capsule; peristome double; exostome teeth pale, linear, imperfect, perforate, sometimes 2-fid, papillose; endostome a low membrane of imperfectly united papillose segments. Calyptra cucullate, or split on one side but gripping the seta below the capsule, naked. Spores papillose.
Species ca. 30 (3 in the flora):
temperate and warm regions nearly worldwide except
Leucodon is distinguished from the other genera of its family by its ecostate leaves and smooth calyptra. Forsstroemia is similar but its plants are more glossy and the leaves are variably costate. Also, according to L. R. Stark (1985) paraphyses are present in the perichaetia of Forsstroemia but lacking in the perichaetia of Leucodon.
SELECTED REFERENCES Crum, H. A. and L. E. Anderson. 1981.
1. Leaves smooth, julaceous and curved; cells near leaf tip papillose-roughened abaxially; branches julaceus, mostly short and simple; clusters of tiny caducous branchlets lacking in leaf axils; capsules mostly well exserted.......1. Leucodon julaceus
1. Leaves more or less plicate wet and dry, sometimes slightly to strongly secund; cells near leaf tip mostly smooth abaxially; branches not julaceus, mostly elongate, simple or branched; clusters of tiny caducous branchlets present or lacking in leaf axils; capsules mostly immersed to barely exserted, or lacking.
2. Caducous branchlets lacking; perichaetia, perigonia, and sporophytes commonly produced; leaves often somewhat secund; leaf cells smooth abaxially; tips of young leaves commonly terminating in a short hyaline cell mostly 21--29 \um long..........2. Leucodon brachypus
2. Caducous branchlets frequent (sometimes scarce or apparently lacking), clustered in upper leaf axils and at branch tips; perichaetia extremely rare, perigonia and sporophytes unknown; leaves only rarely secund; leaf cells rarely slightly papillose abaxially near leaf tip; tips of young leaves commonly terminating in a slender elongate hyaline cell mostly 34--60 \um........3. Leucodon andrewsianus
1. Leucodon julaceus (Hedwig) Sullivant, Musci Allegh. no. 87.1845
Pterigynandrum julaceum Hedwig, Sp. Musc., 81. 1801
Plants medium sized, usually somewhat glossy, lacking fragile branchlets in distal leaf axils. Branches mostly short, rarely elongate, julaceus, mostly curved, rarely straight and rigidly spreading. Branch leaves erect-appressed, not secund, smooth, acute to short-acuminate, mostly 1.1--1.6 mm; cells at leaf tip often papillose abaxially; terminal leaf cell concolorous, mostly isodiametric. Capsule barely exserted to long-exserted, ovoid-cylindric, symmetric, 1.5 mm. Spores 33--40 \um.
Capsules mature October--June, perhaps
all months of the year. Tree trunks,
logs, rarely rock or soil; 0--1460 m; Ont.;
Leucodon julaceus is very common and widespread in much of the eastern portion of the flora area. The usually short, curved, julaceus branches, smooth (nonplicate) leaves, and somewhat glossy aspect are characteristic. Growth forms with slender elongate rhizome-like primary stems bearing widely-spaced short, uncinate branches are very different in appearance from more robust forms with inconspicuous primary stems bearing straight elongate crowded branches. The forms with elongate slender primary sems sometimes form extensive soft tangled mats and then may be mistaken for mosses of other families. In L. andrewsianus and L. brachypus the leaves are longer and more or less plicate; L. julaceus lacks the clustered fragile branchlets of L. andrewsianus. Its capsules are almost always well exserted beyond the perichaetial leaves, while the capsules of L. brachypus are partially immersed. The calyptra of L. julaceus splits along one side and may for a time remain clasping the seta below the capsule. It sometimes grips the tip of the operculum, and when dry lifts the operculum to open the capsule, as in Calymperes (Calymperaceae). Most or all of the spores may escape before the calyptra and operculum finally fall away. In such specimens there are empty capsules still enclosed by the calyptra, with the calyptra still gripping the operculum.
2. Leucodon brachypus Bridel, Bryol. Univ. 2: 210. 1827
Fissidens sciuroides var. vaginans Michaux, Fl. Amer.-Bor. 2: 299. 1803
Plants medium size to robust, dull, lacking fragile branchlets in distal leaf axils. Branches elongate, not julaceus, loosely curved to straight and rigidly spreading. Branch leaves erect-appressed to secund secund, plicate, acute to acuminate, 1.5--2.2 mm; cells at leaf tip smooth abaxially; terminal leaf cell concolorous to hyaline, isodiametric to elongate, mostly 21--29 \um. Capsule immersed to barely exserted, ovoid to pyriform, sometimes slightly asymmetric, to 2 mm. Spores 44--52 \um.
Capsules mature November--July, September; perhaps all year. Tree bark, logs, stumps, rarely rock, upland and montane forests; 0--1950 m; N.B., N.S.; Ala., Ariz., Ark., Ga., Maine, N.H., N.Y., N.C., Ohio, Pa., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.
Leucodon brachypus is easy to distinguish from L. julaceus by its longer, plicate leaves and usually immersed or emergent capsules. It is less common and less widespread than L. julaceus and has a more northern range. The commonly present gametangia and sporophytes, lack of fragile axillary branchlets, and relatively short terminal cell on the leaf tips, distinguish it from the similar L. andrewsianus. In L. brachypus gametangia or sporophytes, or both, are very commonly present. The ranges of L. brachypus and L. andrewsianus overlap and the two species rarely grow intermixed. Leucodon brachypus occurs at sea level in the northren part of its range but only in the mountains to the south, above ca. 300--400 m.
3. Leucodon andrewsianus (H. A. Crum & L. E. Anderson) W. D. Reese & L. E. Anderson, Bryologist 100: 92. 1997
Leucodon brachypus var. andrewsianus H. A. Crum & L. E. Anderson, Bryologist 75: 101. 1972
Plants mostly medium sized, rarely robust, dull or glossy, commonly with conspicuous clusters of short fragile branchlets in distal leaf axils and at branch tips. Branches mostly elongate, not julaceus, curved or rarely straight. Branch leaves erect-appressed, rarely secund, plicate, lanceolate-acuminate, mostly 1.4--1.9 mm; cells at leaf tip rarely papillose abaxially; terminal leaf cell hyaline, usually narrowly elongate, mostly 34--60 \um. Sporophytes unknown.
Tree trunks and rock in forests; 0--1500 m; N.B., Nfld., N.S., Ont., P.E.I., Que.; Maine, Mass., N.H., N.J., N.Y., N.C., Pa., Vt.
Plants of L. andrewsianus differ from those of
the similar and slightly more robust L.
brachypus most evidently in the common presence
of tufts of tiny branchlets congested in axils of distal
leaves and at the branch tips; in some specimens the branch tips and entire
older plants dissolve into branchlets. The branchlets
are mostly very short but sometimes are much elongated. In the absence of the branchlets
the slenderly elongate terminal cells of young
leaves are helpful for identification.
Sporophytes of this moss are unknown and gametangia are extremely rare. Reproduction and dispersion are doubtless
accomplished by the caducous branchlets. This taxon has
been treated in the flora area as Leucodon sciuroides (Hedwig) Schwägrichen,
a moss that occurs in Europe, Africa, and Asia, but apparently not in