Plants reddish black, black or greenish brown. Leaves curved or secund to straight, wide-spreading to squarrose, short-lanceolate, widest proximally, apex oblique or symmetric; costa absent; leaf margins entire; basal laminal cells short- to long-rectangular, marginal cells rounded-quadrate to short-rectangular, walls sometimes thickened, usually pitted, straight; medial laminal cells quadrate to short-rectangular, 1-stratose or occasionally 2-stratose in patches, lumens rounded, rectangular or irregularly stellate; laminal papillae usually present, commonly large, whitish. Sexual condition cladautoicous or autoicous; perichaetial leaves differentiated, convolute-sheathing. Spores 20-32(-50) µm.
In Southern Africa, A. rupestris is identified by its generally red-brown colour, ecostate leaves and frequently papillose leaf cells. The plants tend to vary in size and leaf shape, but specimens are rarely difficult to identify. A broader interpretation of A. rupestris would undoubtedly encompass many of the ecostate species of Andreaea on the sub-Antarctic Islands.
Plants small, forming cushions, red-brown to black-green; saxicolous. Stems 5-20 mm high, irregularly branched; in section round, central strand absent, inner cortical cells in 2-3 rows, corners thickened, outer cells in 2 rows, smaller, round, incrassate. Leaves appressed or with spreading apices dry, erect-spreading wet; ovate to oblong-lanceolate, occasionally constricted above base, 0.3-1.5 mm long; apex weakly cucullate, acute to obtuse; margins entire, incurved; lamina in section unistratose. Costa absent. Upper laminal cells quadrate, incrassate, frequently with strongly thickened corners, smooth to strongly papillose on dorsal surface; basal cells linear to rectangular, irregularly thickened; basal marginal cells short-rectangular to quadrate. Autoicous. Perichaetia terminal; leaves elliptical, 2 mm long; apex obtuse. Pseudopodia 1-2 mm long, pale green; capsule just exserted, elliptical, to 1 mm long, dark red-brown; dehiscence slits extending from mid-capsule to near apex; spores round, 20-25 µm, yellow, weakly papillose.
Plants small, red-brown, forming cushions. Stems 5-20 mm long, irregularly branched. Leaves ovate to oblong-lanceolate; apex acute to obtuse; margins entire, incurved; costa absent. Upper laminal cells quadrate, incrassate, smooth to strongly papillose; basal cells linear to rectangular. Capsule just exserted, pseudopodia 1-2 mm long. Spores weakly papillose. A. rupestris is most easily identified by its red-brown colour, ecostate leaves and frequently papillose leaf cells.
Very widespread in distribution, A. rupestris is also the most commonly collected Andreaea in Southern Africa. This species is known from mountains of the southwestern, central and eastern Cape and the Drakensberg of Lesotho, Natal and the Orange Free State.