The plants are small for Breutelia and might be confused with specimens of Bartramia capensis. The possibility of confusion is further complicated by the variability of the laminal plications. In the type and several other specimens examined, there are 2 plicae, one on each side of the leaf and displaced toward the margins. The plicae are very weak but extend to the upper part of the leaf, while in other specimens the plicae are shorter or even restricted to the extreme base. A couple of specimens even have most of their leaves smooth; it is these specimens that are problematical. A combination of characters, including leaf shape and size, long-excurrent costa, leaf cell thickening and ornamentation, and especially costal anatomy, indicates the relationship between all of the specimens and will help to identify B. angustifolia. These plants might also be confused with B. substricta, however that species has broader leaves and strongly differentiated alar cells.
Plants medium-sized, loosely caespitose, yellowish green, brownish below; terricolous. Stems 10-50 mm long, branches few, occasionally with flagellate branches, tomentum sparse on lower stem, reddish; in section round, central strand present, inner cortical cells in 3-6 rows, thin-walled, red-yellow, slightly thickened toward outside, outer cortical cells in 2 rows, stereids, reddish, epidermal cells thin- walled, fragile, quickly absent and stem fluted. Leaves widespreading to recurved wet or dry; long-acuminate to subulate above ovate to oval base, 2.0-2.5(-3.0) mm long, 0.4-0.5 mm wide in base, plication of lamina variable and weak, plicae extending to upper leaf or very short and restricted to base, occasionally absent on some leaves; margins reflexed to recurved below mid-leaf, serrulate below, serrate above. Costa long- to short-excurrent as denticulate awn, 0.5-1.0 mm long; superficial cells rectangular, smooth, incrassate; in section elliptical to rounded, guide cells 2-4, thickened, ventral cells in single row, stereids or substereids, dorsal stereid or substereid band small, of 4-6 cells, dorsal surface cells substereids. Laminal cells long-rectangular, 5-10:1, strongly incrassate but not pitted or nodose, prorate or papillose at proximal end of cell, occasionally almost smooth; in section surface slightly irregular; basal cells weakly differentiated, long-rectangular, 10-12:1, weakly thickened; alar cells weakly differentiated as slightly shorter and broader cells. Dioicous. Perichaetia lateral through innovation; leaves oblong to oval, abruptly acuminate. Seta 10-15 mm long, reddish yellow; capsule symmetrical, urn globose wet, cylindrical and rugose dry, 1.2-1.5 mm long, red-yellow; exothecial cells quadrate to rectangular or angular, 5-6 rows at mouth transversely rectangular; stomata numerous at base of urn, subphaneropore; peristome double, fragile, only bases of teeth seen, papillose, endostome rudimentary, fragments adhering to exostome, smooth; operculum conic, minutely apiculate; spores rounded, 37-45 µm, warty, brownish.
Plants medium-sized, loosely caespitose. Stems 10-50 mm long, fluted. Leaves patent to recurved, long-acuminate to subulate above oval base, 2-3 mm long, weakly plicate; margins serrate above; costa excurrent as denticulate awn. Upper laminal cells long-rectangular, smooth to prorate or papillose at proximal end; basal and alar cells weakly differentiated. Capsule globose, rugose when dry; peristome double, fragile, endostome rudimentary. Spores warty.