Amorphous cortex, formed of indistinct hyphae with thickened walls; [cf. decomposed cortex].
Amphithecium, thalline margin of the apothecium, [157].
Antagonistic symbiosis, hurtful parasitism of one lichen on another, [261 et seq.]
Apothecium, open or disc-shaped fructification, [11], [156] et passim. Veiled apothecium, [169]. Closed or open at first, [182].
Archilichens, lichens in which the gonidia are bright green (Chlorophyceae), [52], [55] et passim.
Ardella, the small spot-like apothecium of Arthoniaceae, [158].
Areola (areolate), small space marked out by lines or chinks on the surface of the thallus, [73] et passim.
Arthrosterigma, septate tissue-like sterigma (spermatiophore), [197].
Ascogonium, the cell or cells that produce ascogenous hyphae, [180 et seq.]
Ascolichens, lichens in which the fungus is an Ascomycete, [159], [173] et passim.