Didymodon rigidulus
Didymodon rigidulus var. gracilis
rigid didymodon moss
point beard-moss, rigid 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 appressed to weakly spreading when dry, costa usually percurrent to short-excurrent as a rigid subula, short-lanceolate, seldom-lanceolate, base evenly broadened, ovate to elliptic or oblong, proximal cells short-rectangular, distal laminal cells usually papillose, quadrate, with quadrate lumens, occasionally 2-stratose on the margins in patches;
gemmae often present in distal leaf axils.
0.7–1.7 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.
asexual reproduction by axillary, ovate to elliptic, multicellular gemmae.
teeth short and straight to long and twisted.
Didymodon rigidulus
Didymodon rigidulus var. gracilis
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.)
Variety gracilis may sometimes have gemmae and the distal lamina is occasionally 2-stratose in patches, but it differs from var. rigidulus most clearly in its the short- to long-lanceolate leaves. The distal laminal cells are commonly papillose, and their lumens are oval or rounded-quadrate. Because of intergradation, some collections must be assigned to this variety only on the basis of a majority of the characters given in the key. Although leaves in this variety are short in dry habitats, associated with fragile stems, leaf length in collections from moist environments is generally longer. The small distal laminal cells, broad costa to 6 cells in width at mid leaf, and the strong stem central strand serve to distinguish this taxon from Didymodon asperifolius.
(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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