Species of Acarospora in the Aegean
NOTE: The taxonomy of this genus is poorly understood and the treatment below is therefore provisional.

1A Thallus yellow - - - 2
1B Thallus brown (sometimes pale-, greyish to dark-) - - - 3

2A On vertical rockfaces; areoles ca. 1 mm wide; marginal areoles often enlarged and radiating - - - A. hilaris
2B On horizontal or slanting rock faces, often lichenicolous on Diploschistes; areoles ca. 0.5 mm wide; marginal areoles not enlarged - - - A. microcarpa

3A On calcareous rock; areoles usually pruinose, at first at the margins - - - A. cervina
3B On siliceous rock; areoles not pruinose, or pruinose mainly in the centre - - - 4

4A Thallus reduced to thick "thalline margin" around the apothecium; thallus with norstictic acid (K+ y->red) - - - A. subrufula
4B Thallus areoles well developed and much larger than the apothecial discs; norstictic acid usually absent - - - 5

5A Ascocarps several pro areole, remaining punctiform, sometimes elongate - - - 6
5B Ascocarps when fully developed usually 1 pro areole, 0.5 to over 1 mm wide, with flat, sometimes rugulose disc; widespread - - - 7

6A Small, few mm wide thalli lichenicolous on Aspicilia; ascocarps often elongate; above 1000 m alt. - - - A. impressula
6B Thalli larger, usuallly several cm wide, and usually not lichenicolous; ascocarps not elongate - - - A. smaragdula

7A Margin of thallus areoles swollen, black; areoles ca. 0.5 mm wide and thin - - - A. scotica
7B Margin of thallus areoles not swollen, usually pale; areoles ca. 2 mm wide - - - 8

8A Thallus areoles very prominent, wrinkled in the centre with somewhat radiate faults - - - A. strigata?
8B Thallus areoles less prominent, smooth or rugulose - - - 9

9A Thallus areoles contiguous and forming a continuous areolate crust often over 1 dm wide, with enlarged marginal areoles; medulla C+ red - - - A. pseudofuscata
9B Thallus areoles scattered or, when denser, overgrowing eachother; marginal areoles not enlarged; medulla mostly C- (species difficult to recognize, well-developed material needed) - - - 10

10A Thallus areoles ca. 0.5 mm wide; small and inconspicuous, often scattered plants, usually on horizontal rockfaces - - - A. veronensis
10B Thallus areoles ca. 1-2 mm wide; large and conspicuous plants, on steep to vertical rockfaces - - - 11

11A Thallus areoles often scattered, with raised, crenulate margins, often slightly white-pruinose in the centre - - - A. umbilicata
11B Thallus areoles mostly aggregated, upper surface often warted due to crystal aggregation - - - A. nitrophila?