??????? -- Barbula umbrosa C. Muell., Linnaea 42: 340. 1879. -- Trichostomopsis umbrosa (C. Muell.) Robinson, Phytologia 20: 185. 1970. -- Didymodon australasiae var. umbrosus (C. Muell.) Zander, Cryptogamie 2: 400–401. 1981.
Plants to 1.5 cm high, in tufts or dense cushions, green to bright green. Dry leaves appressed or occasionally somewhat crispate. Moist leaves spreading to rather strongly reflexed, to 2.5 mm long, about 5–6: 1, strongly keeled distally. Leaves long lanceolate, gradually contracted from the moderately well-defined ovate base which constitutes 1/3–1/4 of leaf length, ending in a narrowly acute apex. Median cells unistratose throughout or with bistratose streaks near the leaf apex, mostly smooth but occasionally low pluripapillose, to 8 µm broad, in straight rows, lumen/wall ratio about 2: 1, quadrate to short rectangular, 1–2: 1, with rounded lumens due to strong corner thickenings. Cells of margin undifferentiated or somewhat smaller and thicker walled. Basal cells inflated in a large and well demarcated group near the costa, mostly not extending to the margin, arranged in regular rows, hyaline with thin walls, rectangular, to 20 µm broad, 2–5: 1. Ad- and ab-axial surface of costa clothed with short rectangular cells longer than but not well demarcated from those of the lamina. Costa at base 8–10 cells wide and occupying about 1/8 of leaf, not tapering, percurrent to short excurrent. Costa cross-section with well-differentiated epidermal cells on both surfaces, bulging ventrally and semi-circular dorsally, with a single layer of guide cells and with a strong ventral stereid band but without visible differentiation of either stereids or substereids on adaxial surface. Margin not at all decurrent, entire, bistratose throughout most of the limb, recurved. Gemmae occasional in lower leaf axils, multicellular, red brown, nearly spherical to elliptical, to 75 µm in diameter. Axillary hairs to 100 µm, 4–5 celled with one basal brown cell. Stem rounded pentagonal in cross-section, with central strand, and with thin-walled inner cortical cells grading to 1–3 layers of somewhat thicker walled, smaller outer cortical cells, with a distinct hyaloderm. Rhizoids smooth, pale brown, sparingly branched, mostly restricted to base of plant, to 10 µm wide at insertion.
Dioicous. Perichaetial leaves mostly somewhat sheathing but otherwise not significantly different from vegetative leaves. Setae to 10 mm, yellow- to reddish-brown, straight, smooth. Capsule erect and symmetrical with the urn cylindrical, to 2 mm long, about 3–4: 1. Operculum conic to short rostrate, to 2/3 of urn length. Exothecial cells with rather thin walls, rectangular, not in regular rows, to 25 µm wide, 2–4: 1, isodiametric, smaller and thicker-walled near mouth. Annulus of 1–2 rows of vesiculose cells, persistent or falling in fragments. Peristome reddish-brown, to 500 µm long, divided to base, without or with a very low basal membrane, with the segments papillose-spiculose throughout, straight to strongly spiral. Spores spherical, about 12 µm, low papillose to nearly smooth.