BFNA Title: Helodium
 Author: P. M. Eckel
Date: April 3, 2012
Edit Level: R
Version: 1

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


Plants small to rather robust, in soft, loose green or yellowish or brownish green tufts or mats. Stems creeping to spreading and erect-ascending, regularly 1(--2) pinnate, not stipitate, forming a flat frond with a strong primary axis, branches distally tapered; stem section with hyalodermis lacking, sclerodermis of 3(--4) thick-walled cells, central cylinder of large, firm-walled cells, with or without a small central strand; paraphyllia densely felting stems and branches, filiform to narrowly foliose, marginal cells ciliate or toothed and ciliate, cell surface smooth; terminal cell (15--)20--25(--30):1; pseudoparaphyllia lanceolate-foliose, marginal cells ciliate or toothed and ciliate, cell surface smooth or proximally 1-papillose, the apical cells of both paraphyllia and pseudoparaphyllia long and sharply acute, without papillae; rhizoids smooth or minutely papillose, scattered on stems between the leaves or at tips of branches; axillary hairs with 1--2 short, brown basal cells and 2--3(--4) hyaline oblong distal cells. Stem leaves erect to erect-spreading when moist, ovate-lanceolate, rounded-cordiform to triangular-cordate, base abruptly narrowed to the insertion, scarcely to distinctly narrowly decurrent, abruptly to more gradually acuminate beyond the middle,  concave, striate to plicate-sulcate; margins strongly and irregularly recurved, proximal margins fimbriate-ciliate, median and distal margins serrulate-dentate to crenulate more or less throughout; costa single, strong, ending at base of or before the acumen or near the apex, rarely excurrent, smooth or with low or coarse teeth on the proximal surface, paraphyllia usually abaxial at base; stem leaf cells pellucid, subquadrate to long-rectangular, thin-walled or incrassate, adaxially essentially smooth to low or coarsely 1-papillose, abaxially 1-papillose centrally over the lumen or more often near the distal ends to prorulose, never pluripapillose, apical cells sharply pointed and smooth; alar cells not or poorly differentiated. Branch leaves mostly similar to stem leaves but shorter, becoming ovate (not triangular-cordiform) in Echinophyllum, with smooth, elongate apical cells. Specialized asexual reproduction absent. Sexual condition dioicous or autoicous; perigonia and perichaetia seated and lateral on the stems, perichaetia erect, oblong-lanceolate, abruptly and slenderly long-acuminate, plicate; margins of perichaetial leaves subentire proximally, distally irregularly denticulate to shortly ciliate, recurved on one or both sides, with costa ending in the acumen before the apex, distal cells linear or oblong-linear, smooth to minutely prorulose, walls thin or incrassate. Seta elongate, smooth, reddish orange. Capsule strongly inclined to horizontal, arcuate and asymmetric, or straight, cylindric; annulus differentiated, well-developed, revoluble, of (2--)3-4 rows of cells; operculum straight, conic or rostellate-rostrate, blunt or apiculate; peristome hypnoid; peristome teeth yellow to yellow-brown; exostome teeth 16, lanceolate, yellowish, connate and cross-striolate proximally, papillose distally; endostome segments lanceolate, hyaline to yellow, basal membrane high, distal segments alternating with groups of (2--)3--4  long, slender, subcoalescent, appendiculate or nodulose cilia. Calyptra cucullate, naked. Spores globose, minutely papillose (10--)11--15(--16) \um.


Genera 4 (2 in the flora): mostly temperate zone, Northern Hemisphere.


Genera of Helodiaceae are generally branching once-pinnate from a single axis, have a single costa to the leaf middle or beyond, and rather elongate median leaf cells, (5--)7--10(--18):1. Abaxial portions of the stem leaves are smooth, or with a single, central papillae over the lumina, but all generally are characterized by papillae located at or near the distal end of the cell, or the cells are prorulose, or both. Stem and branch leaf apical cells are essentially smooth and sharply pointed (not truncate or multi-papillose). The stems are somewhat to densely tomentose with conspicuous complex slender smooth-walled paraphyllia and smooth to proximally unipapillose pseudoparaphyllia whose apical cell is also sharply pointed and smooth on surface and margins. These structures also develop as appendages from the proximal margins of the stem and branch leaves. Strong, pointed teeth in the proximal region, as in H. blandowii and Echinophyllum, are variously antrorsely and retrorsely curved. Leaves of the Helodiaceae characteristically have fimbriate, elongate, paraphyllia-like appendages at the basal margins of the stem leaves. The terminal cell of the paraphyllia of species of Thuidium (Thuidiaceae) as well as that of the branch leaves is (sub)quadrate, truncate and multipapillose, the apical cell coronate-papillose, not smooth and sharply pointed as in species of  Helodium and Echinophyllum.


Heterocladium has an indistinct or short (ending at the leaf middle or before) and simple, or double leaf costa. Haplocladium also has a similar terminal paraphyllia cell, but with sparse to abundant paraphyllia with short, subquadrate cells, and with leaf cells abaxially bearing a single, stout papilla over the lumen. Claopodium has no or few and inconspicuous paraphyllia and a papillose seta. Thelia (Theliaceae) species have terete-julaceous habits, complex-branched laminal papillae, erect leaf margins, peristomes that are densely papillose and lack cilia, or, in Thelia hirtella, with long, regularly antrorsely curved unbranched papillae on the distal leaf margins.


According to W. Frey (2009), the separation of the Helodiaceae from the Thuidiaceae is not substantiated by molecular analyses, although there are rather distinct morphological differences between the Helodioid genera, and the Thuidioid---Helodioid genera have median or distal cells, or both, linear-rhomboidal, with alar cells differentiated, but otherwise the plants are very similar.

Helodiaceae is retained as a family by B. Goffinet et al. (2009), and clearly the family is in the process of definition. Crosby et al. (1999) cited four genera for the family, including Helodium, Echinophyllum (as Bryochenia), Actinothuidium, and Palustriella.


SELECTED REFERENCES  Best, G. N.  1896. Revision of the North American Thuidiums. Bull. Torrey Bot. Cl. 23: 78--90. Crosby, M. R., R. E. Magill, B. Allen, and Si He. 1999. A Checklist of the Mosses. Release Dec. 20, 1999. St. Louis. Goffinet, B., W. R. Buch and A. J. Shaw. 2009. Morphology, anatomy and classification of the Bryophyta. In B. Goffinet and A. J. Shaw, eds. Bryophyte Biology, Second Edition. Cambridge. Pp. 55--138. Frey, W., ed. 2009. Syllabus of Plant Families: A. Engler's Syllabus der Pflanzenfamilien. Part 3. Bryophytes and seedless Vascular Plants. Berlin.


1. Autoicous;  strictly 1-pinnate, median stem leaf cells elongate, mostly 7--10(--18):1; costa of stem leaf essentially smooth or with 1--2 teeth over the surface in proximal half; inner perichaetial leaves without cilia, apical cell of stem and branch leaves 6--7:1; abaxial leaf cells roughened with small and delicate papillae; stem and branch leaves similar in shape; paraphyllia with minute denticulations on the distal cell ends of the cilia, branched-filiform . . . 1. Helodium, p. XXX


1. Dioicous; irregularly 1--2-pinnate; median stem leaf cells subquadrate to short-rectangular, mostly (5--)6:1; costa of stem leaf with coarse, spinose teeth over the surface in proximal half; inner perichaetial leaves ciliate; apical cell of stem leaves ca. 20:1, branch leaves ca. 7:1; abaxial leaf cells echinate with coarsely obliquely blunt-conic papillae; stem leaves cordiform, branch leaves ovate; paraphyllia with irregular coarse teeth on the cilia margins, laciniate-foliose and branched-filiform . . . 2. Echinophyllum, p. XXX


1. HELODIUM  Warnstorf, Krypt.-Fl. Brandenburg, Laubm., 675, 692. 1905, conserved name * [Greek (h)elos,  low ground by a river, a marsh or marsh-meadow, eidos, resemblance, and Latin -ium, diminutive noun suffix, alluding to the habitat]

Patricia M. Eckel


Plants medium to large, in soft, loose, tufts or mats, green to yellow-brown. Stems ascending to erect, freely branched and regularly 1-pinnate, with or without a stem central strand; paraphyllia densely felting stems, branches, leaf bases, the abaxial surface of the costa at the leaf base, both filiform and narrowly lanceolate-foliose, (1--)2(--3) seriate at insertion, cell surface smooth, simple, more often branched, cells long-rectangular, to 20:1, marginally essentially smooth to distally 1-papillose or prorulose at cell ends only, terminal cell lanceolate, smooth, thin-walled or somewhat thicker-walled at the tip; pseudoparaphyllia lanceolate-foliose, cells (1--)2--4(--5)-seriate at the insertion, 3--5(--7) cells elongate, with margins serrulate with lateral teeth, proximal cells subquadrate, short- to long-rectangular, cell surface smooth, terminal cell as in paraphyllia. Stem and branch  leaves erect or erect-spreading, ovate-lanceolate to rounded-cordiform, abruptly to gradually tapered into a flat or channeled, broad or attenuate, often twisted acumen; proximal margins irregularly revolute  or strongly and broadly or narrowly revolute to the apex; proximal to median margins fimbriate-ciliate with paraphyllia-like appendages, medially entire and minutely toothed near the apex; or with short, sharp teeth from projecting distal cell ends throughout; costa single, rather strong, ending at or before the acumen base, or in the acumen, or rarely percurrent, essentially smooth or with 1--2 teeth near the insertion; stem leaf cells pellucid, enlarged and laxly rectangular along the insertion, medially and distally thin-walled or incrassate, length heterogeneous, mostly linear-rectangular to linear-fusiform, 7--10(--18):1, apical cell of stem and branch leaves 6--7:1; adaxially smooth or 1-papillose, abaxially 1-papillose centrally over the lumen or more often near the distal ends, apical cell variously distally somewhat thickened, sometimes with a low papilla. Sexual condition autoicous; perichaetial leaf margins subentire proximally, eciliate, distally regularly denticulate or irregularly and sharply dentate. Capsule  smooth, brown, stomata present in the short neck.


Species 2 (2 in the flora): Greenland, North Temperate Zone.


The marginal cells of the leaf in the acumen of both species of Helodium are shorter than the cells in the middle of the acumen and converge at the apex to produce a smooth cell generally shorter than other cells in the acumen. In Echinophyllum sachalinense the smooth apical cell of the acumen becomes more elongated than the cells proximal to it in both stem and branch leaves. In Echinophyllum the pseudoparaphyllia are papillose, but smooth in Helodium. The distal medial cells of the stem leaves are short and thick-walled (parenchymatous), but long-rectangular and relatively to distinctly thin-walled (prosenchymatous) in Helodium (T. O’Brien and D. Horton 2000). The cells near the base of the costa are larger and laxer, and more pale than cells distal to this area, whereas in Echinophyllum they are thick-walled and short-rectangular to  (sub)quadrate and concolorous. The perichaetial leaves of the two species of Helodium are nearly smooth throughout and bordered by minute, uniform denticulations, or sharply, distantly and irregularly toothed from distal cell ends. In Echinophyllum, the margins are sparsely short-ciliate with hyaline, long-celled, narrow teeth composed of (1--)2 elongate cells, free but closely parallel to the edge of the lamina. When dry, the dense paraphyllia felting the stems appear like cobwebs. The habitat of Helodium blandowii is mostly hydric, associated with wet substrates, whereas Echinophyllum occurs in more mesic places, on drier humus, bark or rock (T. O’Brien and D. Horton 2000). Helodium paludosum seems to be intermediate in habitat preferences and able to tolerate seasonal desiccation.


SELECTED REFERENCES  Abramova, A. L. and I. I. Abramov. 1972. On the span of the genus Helodium (Sull.) Warnst. J. Hattori Bot. Lab. 35: 371--381. O’Brien, T. J. and D. Horton. 2000. Bryochenea (Musci; Thuidiaceae) is Cyrto-hypnum (Thuidiaceae), but B. sachalinensis is Echinophyllum (Thuidiaceae), a new genus from the Pacific Rim. Bryologist 103:509-517. Watanabe, R. 1972. A revision of the family Thuidiaceae in Japan and adjacent areas. J. Hattori Bot. Lab. 36: 171--320.


1. Stem without central strand; paraphyllia long, dense, floccose; leaves shortly rounded-cordate; stem leaves short-acuminate; leaves yellow, yellow-green, often bright red-orange at insertion and paraphyllium bases; stem leaf cells rather thick-walled, rounded at the corners, abaxially strongly 1-papillose centrally or nearer the distal ends of the lumen; costa with 1--2 scattered teeth along the proximal abaxial surface . . . . 1. Helodium blandowii  


1. Stem with central strand; paraphyllia scattered and short; leaves longly ovate-lanceolate; stem leaves slenderly long-acuminate, pale green, nearly hyaline at insertion and paraphyllium bases; stem leaf cells rather thin-walled, angular at the corners, abaxially essentially smooth or weakly papillose because of projecting distal angles; costa essentially smooth proximally. . . . .2. Helodium paludosum


1. Helodium blandowii (F. Weber & D. Mohr) Warnstorf, Krypt.-Fl. Brandenburg Laubm., 692. 1905


Hypnum blandowii F. Weber & D. Mohr, Bot. Taschenbuch, 332. 1807



Plants rather large in yellow to yellowish-green mats. Stems red-brown, closely and strictly 1-pinnate, more loosely pinnate in one variety; branches simple, nearly equal, straight, widely spreading, paraphyllia abundant on stems and branches in long, tangled masses, central strand absent. Stem and branch leaves rather close and overlapping, more erect than spreading when moist, rounded-cordiform, stem leaves 1.2--1.5 mm, branch leaves 0.6--0.8 mm, both sulcate-plicate, rather abruptly tapered into a broad, channeled, rather short acumen, margins erect-incurved in the acumen, denticulate with short, sharp teeth from projecting distal cell ends throughout; costa with 1--2 scattered teeth along the proximal abaxial surface; stem leaf cells incrassate, oblong-fusiform or oblong-rhomboidal, with rounded angles, abaxially strongly 1-papillose centrally or nearer the distal ends of the lumen. Perichaetial leaves with short, irregularly spaced, distant, sharply variously antrorsely to retrorsely pointed teeth on distal margins, regularly denticulate in the acumen. Seta 40--60 mm. Capsule 3-4 mm.


Varieties 2 (2 in the flora): Greenland, North Temperate Zone.


The marginal teeth of the leaves of Helodium blandowii, especially proximally and medially, are sharply dentate-serrate, whereas the margins of H. paludosum are nearly smooth. The papillae, though narrow, are elevated and, especially as seen on branch leaves, antrorsely curved, like those in Echinophyllum, but much more delicate. The length of the seta of H. blandowii (4--6 cm)  is more than twice that of H. paludosum (2--2.8 cm) and the capsules are larger (3--4 mm in H. blandowii, but 2--2.5 mm in H. paludosum).


1. Stems erect, evenly and strongly pinnate, with branches nearly equal; costa ending at or before base of leaf acumen . . . . 1a. Helodium blandowii var. blandowii

1.  Stems spreading, loosely subpinnate, with unequal branches; costa ending near the leaf apex . . . . 1b. Helodium blandowii var. helodioides  


1a. Helodium blandowii var. blandowii


Stems erect, evenly and closely pinnate, branches subequal, costa ending at the base of or before leaf acumen.


Capsules mature spring. Hydric soils of open or wooded fen, muskeg, wet habitats, along streams, edges swamp forests, open fens, wet bases of trees in hummocks in peat bogs and bogs of Thuja occidentalis, tundra benches and gravel bars of creeks, calciphile; moderate to high elevations; Greenland; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld. and Labr.), N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Conn., Ga., Idaho, Ill., Iowa, Maine, Mass., Mich., Minn., Mont., Nebr., Nev., N.J., N.Y., N.C., N.Dak., Ohio, Oreg., Pa., S.Dak., Utah, Vt., Wash., Wis., Wyo.; Eurasia.


1b. Helodium blandowii var. helodioides (Renauld & Cardot ex Röll) H. A. Crum, Steere & L. E. Anderson, Bryologist 68: 432. 1965 [1966]  E


Thuidium helodioides Renauld & Cardot ex Röll, Hedwigia 32: 308. 1893; Elodium paludosum var. helodioides (Renauld & Cardot ex Röll) Best; Helodium paludosum var. helodioides (Renauld & Cardot ex Röll) Grout


Stems spreading, loosely subpinnate, with unequal branches, costa ending near the leaf apex.


Soil, logs, swampy woods; moderate elevations; Ont.; Ind., Iowa, Mass., Mich., N.J., N.Y., Ohio, Pa; Vt.


Thuidium helodioides was regarded by A. J. Grout (1934) as a variety of H. paludosum as did Best (1896) before him. The variety was transferred from H. paludosum to that of H. blandowii by H. A. Crum et al. (81965) in preparation for their checklist of North American mosses. According to G. N Best (1896) the variety was growing with the typical variety (of Helodium paludosum var. paludosum). The spelling of the varietal epithet follows Art. 60A of the ICBN (McNeill 2006), which recommends classical usage and the transcription of the Greek spiritus asper as the letter h, correcting the common variant “elodioides.”


SELECTED REFERENCES Grout, A. J. 1934. Leskeaceae. In A. J. Grout, ed. Moss Flora of North America North of Mexico. 3: 179--180. Newfane, Vermont. Crum, H., W. C. Steere and L. E. Anderson. [1966] 1965. Some additional new names for North American mosses. Bryologist 68: 432--434. Grout, A. J. 1934. Leskeaceae. In A. J. Grout, ed. Moss Flora of North America North of Mexico. 3: 179--180. Newfane, Vermont. McNeill, Chairman. 2006. International Code of Botanical Nomenclature (Vienna Code). Ruggell, Liechtenstein.


1. Helodium paludosum (Austin) Brotherus in A. Engler & K. Prantl, Nat. Pfanzerfam. 1(3): 1019. 1908


Elodium paludosum Austin, Musci Appalach., 306. 1870; Thuidium paludosum (Austin) Rau & Hervey


Plants of medium size, rather delicate, in pale green or yellow-green mats. Stems green, loosely 1-pinnate; branches often unequal, flexuose, widely spreading, paraphyllia scattered and short, central strand present. Stem and branch leaves rather distant on the stem, wide-spreading when moist, ovate-lanceolate, stem leaves 1.5--1.8 mm, branch leaves 0.9--1.5 mm, both striate-plicate, rather gradually slenderly tapered into a rather long, flat acumen, margins plane in the acumen, nearly smooth proximally and minutely serrulate or sinuate-serrulate distally; costa smooth, 4/5 leaf length, subpercurrent; stem leaf cells rather thin-walled, long-rectangular to linear, angular at the corners, abaxially essentially smooth or weakly papillose-prorulose because of projecting distal ends of the lumen. Perichaetial leaves regularly denticulate on distal margins. Seta 20--28 mm. Capsule 2--2.5 mm.


Capsules mature spring. Hydric soils of fens, marshes, hummocks in swamps, logs, base and roots of Alnus, seepage, depressions in wet woods and thickets, grassy wet  meadows and bottomlands, wet tree bases, Taxodium distichum swamps in southern areas, often near springs, dry summer soils, seasonally submerged, seasonally wet areas, dried sinkhole ponds, tops of hills and mountains in brushy marshes; low to moderate elevations; B.C., N.S., Ont., Que., Ala., Alaska, Conn., Del., Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., Tenn., Vt., Va., W.Va., Wis., e Asia.


Helodium paludosum is sometimes difficult to distinguish from H. blandowii in the southern part of its range, but the key above is usually adequate. The latter tolerates drier situations (H. N. Best 1896).