Sterile specimens can be distinguished from A. muscicola by the compactness of the assimilation tissue and from A. wilmsii, by its smaller size and the lanceolate appendages (occasionally double) of the purple or reddish purple ventral scales and from A. marginata by its generally purple, not wide, black thallus margins and by its mostly summer rainfall distribution.
Thalli smallish to quite large, in crowded mats; light green, rather crystalline to shiny, firm and compact, faintly areolate or not, air pores tiny, scattered, margins turning purple, slightly scalloped, somewhat undulate; when dry, thallus margins raised or inflexed, sometimes inrolled. Branches simple or occasionally once, rarely several times pseudodichotomously furcate, often with apical or ventrolateral innovations, broadly ligulate, widening rapidly from narrow base, 18-25 mm long, (1.9-)2.5-4.0 (-4.9) mm wide, (450-) 500-600 (-775) µm thick medianly, in section 5 or 6 times wider than thick, apex notched, tips of ventral scales recurved over edge; groove absent, thallus dorsally flat, margins acute, thin; flanks sloping obliquely, red to deep purple; ventral face medianly keeled, green. Scales in 2 ventral rows, obliquely triangular, red to deep purple, body up to 1000 µm long, margins ± entire, base crescentic, ± 1500 µm wide, narrowed above and constricted where joined to single lanceolate appendage, occasionally 2, 450-650 (-800) µm long, 150-200 µm wide basally, tapering above to conical apical cell, ± 8 or more small, colourless oil cells scattered throughout scale. Dorsal epidermal cells unistratose, generally containing chloroplasts, thin-walled, (4-)5- or 6-sided, (30.0)-50.0-67.5(-90.0) x 22.5-30.0 µm; air pores slightly raised, simple, ± 17.5 x 12.5 µm, surrounded by innermost ring of small collapsed cells, then by 2 concentric rings of 6-8(-10) larger cells in each, radial walls not thickened. Assimilation tissue up to 280 µm thick, air chambers small, empty, in 2-4 storeys, bounding walls chlorophyllose; storage tissue mostly confined to keel, cells closely packed together, walls thick and pitted; oil cells scattered throughout tissues. Dioicous, rarely autoicous. Androecia naked, sessile, elongated or oval cushions, medianly near apex of main branch, rarely also at ± midlength constriction, sometimes on short apical or lateral innovations, antheridia immersed, opening above into stout, raised, purple-red papillae. Gynoecial receptacles proximal to apical notch of main branch or rarely on short ventrolateral innovations, single, occasionally paired at apices of 2 furcate branches, almost sessile when young, with numerous (± 75), long, pale, sometimes purple paleae arching over disc, at maturity raised on stalk; carpocephalum rounded, ± 3 mm across when bearing 4 or 5 capsules, frequently with only 1 or 2 and then smaller, above with numerous prominent papillae, containing air chambers which open via compound air pores. Stalk arising 1.5 mm proximal to apex of branch in apical notch, length variable, (1-)5-13(-20) mm long, at midlength ± 550 µm wide, widening toward base, whitish to purple, with single rhizoid furrow, at summit ± 32 slender, shaggy paleae, white or purple, up to 3250 µm long, 4 or 5 cells wide at base, gradually tapering to conical apical cell. Involucre membranous, partly covering capsule below. Pseudoperianths descending obliquely downward and extending ± 1000 µm beyond involucre, generally split into 14 cage-like segments, shiny white or purple-stained, tapering to narrow, connate tips. Sporophyte with globose capsule, ± 1000 µm diam., wall unistratose, lacking thickening bands, dehiscing along well-defined line. Spores 102.5-125.0 µm diam., triangular-globular, mostly yellow, sometimes brown, translucent; wing undulate, up to ± 20 µm wide, margin crenulate; distal face convex, with network of 6-8 angular alveoli across, 20-30 µm wide, ridges 7.5-10.0 µm high and laterally extending across wing, floor of alveoli highly porate and generally with smaller subsidiary alveoli, these also extending over crests of main ridges; proximal face with prominent triradiate ridge, its arms ± 15 µm high, continuous from pole and across wing to margin, each of 3 facets with alveoli, ± 10 µm wide, also extending across wing and containing many or few, smaller, subsidiary alveoli that cross over crests of main alveoli and onto wing to margin which is finely ornamented on both faces. Elaters 142-165(-180) µm long, 15 µm wide in centre, slightly tapering to ends, bispiral, yellow.