Plants reddish brown to black. Leaves erect-spreading to squarrose, straight, panduriform, widest distally, apex symmetric; costa absent; leaf margins denticulate along leaf base; basal laminal cells rectangular to long-rectangular, marginal cells similar, walls pitted, nodose; medial laminal cells rounded-quadrate to ovate, 1-stratose entirely or sometimes 2-stratose distally, lumens rounded; laminal papillae rare, low. Sexual condition cladautoicous; perichaetial leaves differentiated, convolute-sheathing. Spores 18-28 µm.
Andreaea alpina, along with A. acuminata and A. gainii, are rare species that are known in Australia only from Tasmania. They can grow in similar habitats and all have leaf base margins that are crenate or toothed; A. acuminata and A. gainii also tend to have leaves with abruptly formed, triangular apices similar to those of A. alpina. Most collections of A. alpina have been misidentified as A. acuminata, but A. alpina differs by its usually stiffer, more symmetrical leaves with a more sharply formed, characteristically incurved, triangular apex. It also has much larger spores, and male plants have numerous paraphyses. Andreaea alpina differs from the very rare A. gainii by its leaves with basal marginal cells oblique and crenate or toothed almost to the insertion. It also tends to have leaves with basal median cell lumina clearly narrower than the walls and with a more abruptly formed apex. Until an analysis of the significance of the considerable variability, worldwide, of A. alpina is completed, A. montana is best treated as a synonym. It differs from A. alpina s. str. by its larger range of spore size and leaves that can sometimes be less stiff with longer, more secund apices.
Stems 1-6(-8) cm long. Leaves panduriform, mostly 0.4-0.5 mm wide, widest in mid-leaf, 2-2.5 times as long as wide; blade straight, usually not secund, sometimes flexuose; apex usually inflexed or plane, acute, not rounded, with a ±abrupt broad terminal triangular area occupying 25-33(-50)% of the length of the leaf; sinus strongly contracted; margin incurved to plane, proximally crenate or toothed (1 or 2 most proximal cells sometimes entire); base distinctly sheathing; costa absent; laminal cells heterogeneous, distally smooth (or slightly bulging), locally bistratose or unistratose, proximally marginally mostly rectangular, mostly oblique.Perigonial paraphyses present. Perichaetial bracts convolute and sheathing. Capsule base shorter than valves. Turgid spores 26-58 µm diam.; shrivelled spores 17-48 µm diam.
Occurs in Tas., widely distributed in the Southern Hemisphere: New Zealand, Macquarie Is., Auckland Is., Kerguelen Is., Gough Is., Marion Is., Tristan da Cunha, South Georgia, Falkland Is. and South America; also in north-western Europe and Greenland.