Didymodon rigidulus
Didymodon johansenii
rigid didymodon moss
johansen's beard moss, johansen's didymodon moss
leaves appressed-incurved to weakly spreading when dry, spreading or not and not keeled when moist, monomorphic, long-ligulate, ovate-lanceolate, elliptic-lanceolate or long-lanceolate, broadly channeled across leaf or occasionally somewhat channeled along costa, 0.8–1.7(–3) mm, base scarcely differentiated to ovate, margins recurved in proximal 1/4–3/4, entire, apex acute to subulate, occasionally fragile;
costa percurrent to excurrent as a long, thick, blunt subula, not much widened or tapering through the leaf, not strongly spurred, lacking a bulging adaxial pad of cells, adaxial costal cells quadrate, in (2–)3–4(–5) rows, guide cells in a single layer;
basal laminal cells weakly differentiated medially, rectangular, walls thin to evenly thickened, proximal maginal cells little differentiated;
distal laminal cells mostly 8–11 µm wide, 1:1, papillae absent or simple or occasionally 2-fid, lumens oval to rounded-quadrate, walls evenly thickened, moderately bulging on both sides or only abaxially, sometimes 2-stratose marginally or at apex of leaf, or throughout lamina.
leaves erect-appressed when dry, spreading and not keeled when moist, monomorphic, oblong-lanceolate, adaxially weakly concave across leaf, 0.7–1.1 mm (excluding the deciduous tip) to 2.5 mm whole, base scarcely differentiated in shape, margins recurved at mid leaf, entire, apex thickened, long-cylindric to clavate, seldom a long, filiform excurrency, usually soon deciduous, constricted in places, absent in mature leaves;
costa excurrent, excurrency absent in mature leaves, not much widened or tapering at mid leaf but swollen in excurrency, pad of cells absent, adaxial costal cells elongate at mid leaf but quadrate near apex, 2–4 cells wide at mid leaf, guide cells in 1 layer;
basal laminal cells differentiated medially, walls thin;
distal laminal cells 13–15 µm wide, 1:1, papillae absent, lumens often angular, walls thin to irregularly thickened, weakly convex on both sides, 1-stratose except in deciduous apex.
0.7–1.7 cm.
0.35–0.50 cm.
1–2 mm;
peristome teeth 32 or 16 cleft to base or rudimentary or occasionally absent, filamentous or long-triangular, straight or weakly twisted, to 740 µm. Spores 9–12 µm. Distal laminal KOH reaction yellow- or red-orange.
0.75–1.00 mm;
peristome teeth 16, linear, cleft to near base, straight to weakly twisted, ca. 200 µm. Spores 15–18 µm. Distal laminal KOH reaction red.
asexual reproduction by axillary, ovate to elliptic, multicellular gemmae.
asexual reproduction by the deciduous leaf apex.
Didymodon rigidulus
Didymodon johansenii
Varieties 6 (5 in the flora).
Didymodon rigidulus in the broad sense, as emended by R. H. Zander (1981b) is polymorphic, with several varieties distinguished by fairly good correlations of combinations of characters. Specimens of intermediate morphology that are not clearly assignable to any one variety may be identified as D. rigidulus in the broad sense. Although some authors use the presence of axillary gemmae as diagnostic of the typical variety, other varieties, notably var. gracilis, may occasionally have them. Such gemmae are also found in other species, especially those of the D. vinealis complex. Didymodon vinealis may have 2-stratose distal laminal cells, and should be carefully distinguished.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Distinctive characters of Didymodon johansenii are the striate peristome teeth, deciduous, clavate leaf apex and large, trigonous laminal cells. Most collections of it lack the propaguliform apex in all but the most immature leaves, and the leaves are oblong-lanceolate. Some specimens (e.g., Northwest Territories: Scotter 22404, MICH), however, approach D. ridigulus var. icmadophilus in the green color, ovate leaf base, and apparently nondeciduous leaf apices. These collections can be rightly placed by the presence of claviform apices in at least some leaves (especially those near an inflorescence) and the large distal laminal cells, which often have trigones. Didymodon nigrescens has fragile, clavate tips to its perichaetial leaves, but the crenulate distal leaf margins and very thin costa will distinguish it.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Lamina 2-stratose in distal 1/2-3/4 | var. subulatus |
1. Lamina 1-stratose or 2-stratose only at the extreme leaf apex or on the distal margins | → 2 |
2. Leaves oblong-lanceolate, elliptic-lanceolate or occasionally long-triangular; costa usually short-excurrent and blunt; apex and distal margins generally 2-stratose; gemmae often present | var. rigidulus |
2. Leaves short-lanceolate to lanceolate; costa percurrent to long-excurrent, usually sharp; distal margins 1-stratose or less commonly 2-stratose in patches; gemmae usually absent | → 3 |
3. Plants flagellate, leaves strongly appressed when dry, linear-lanceolate; costa long-excurrent | var. ditrichoides |
3. Plants thickly leaved, leaves appressed to spreading when dry, short-lanceolate to long-lanceolate; costa percurrent to long-excurrent | → 4 |
4. Leaves short- to long-lanceolate; base evenly broadened, square or rectangular; costa usually percurrent to short-excurrent as a rigid subula, seldom-excurrent; distal cells generally papillose, oval or rounded-quadrate; proximal cells short-rectangular; gemmae occasionally present | var. gracilis |
4. Leaves long-lanceolate; base abruptly broadened, ovate; costa usually long-excurrent as a straight or flexuose, often fragile subula; distal cells usually smooth, usually angular; proximal cells usually quadrate; gemmae very rare | var. icmadophilus |
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