Megasporaceae key (Aspicilia, Circinaria, Lobothallia, Megaspora and Sagedia)
Key adapted from Fletcher et al. (2009). The phylogenetic placement is uncertain of some species currently assigned to Aspicilia sensu stricto as no molecular data are available.
| 1 | Ascospores very large (usually 35-50 x 25-40 µm); thallus crustose, on calcareous soils, bryophytes or plant debris | Megaspora verrucosa |
| Ascospores small to medium-size (rarely >30 µm long); thallus crustose, foliose or placodioid, on acid or calcareous rocks | 2 | |
| 2 (1) | Thallus mostly foliose or placodioid; ascospores 10-15 μm long; conidia 3-6 μm long (Lobothallia) | 3 |
| Thallus crustose, sometimes radiating; ascospores almost always > 13 µm long; conidia > 6 µm long | 5 | |
| 3 (2) | Thallus foliose, Physcia-like; K-, Pd-; on quartzite rocks in montane freshwater habitats, NW Scotland | Lobothallia melanaspis |
| Thallus placodioid or crustose | 4 | |
| 4 (3) | Thallus radiating, placodioid, lobate at the margins; K+ red, Pd+ orange; on calcareous rocks and man-made substrata, widely distributed | Lobothallia radiosa |
| Thallus crustose, areolate, coarsely warted, dark blue-grey or brown, the ascomata large and often obscuring areolae; K-, Pd-; on maritime rocks, widely distributed but rare | Lobothallia recedens | |
| 5 (2) | On limestone, cement or base-enriched rocks | 6 |
| On siliceous rocks | 8 | |
| 6 (5) | Areoles circular, widely separated especially at margin; prothallus very thin | Circinaria contorta subsp. contorta |
| Areoles ± angular, forming a continuous crust to edge of thallus; prothallus usually evident | 7 | |
| 7 (6) | Thallus margin abrupt, usually zonate; areoles elongated, separated by radiating cracks, cortex smooth | Circinaria calcarea |
| Thallus margin effuse; areoles rimose, regular, lacking radiating cracks at edge, cortex scabrid | Circinaria contorta subsp. hoffmanniana | |
| 8 (5) | Thallus dark grey, with circular white soralia | Aspicilia grisea |
| Thallus without soralia | 9 | |
| 9 (8) | Thallus Pd+ orange, K+ yellow or red | 10 |
| Thallus Pd–, K– | 13 | |
| 10 (9) | Thallus smooth, glossy, dark green-black; aquatic | Aspicilia laevata |
| Thallus cracked-areolate, not glossy, shades of grey or brown, on open, dry rock | 11 | |
| 11 (10) | Ascospores 11-16 µm long; conidia 11-16 µm long | Aspicilia cinerea |
| Ascospores > 20 µm long | 12 | |
| 12 (11) | Conidia 7-11 μm long; ascospores 22-28 μm long | Aspicilia intermutans |
| Conidia 15-28 μm long; ascospores 20-25 μm long | Aspicilia epiglypta | |
| 13 (9) | On rocks in freshwater habitats | 14 |
| On terrestrial rocks | 15 | |
| 14 (13) | Thallus thick, dark grey, sometimes forming concentric rings; prothallus black; ascospores (14.5-) 17-20.5 (-22.5) x (7-) 8.5-11.5 (-13.5) µm | Sagedia zonata |
| Thallus thin, white or yellowish with a thick grey prothallus; ascospores 25-35 × 14-20 μm | Aspicilia aquatica | |
| 15 (13) | On sea-bird perches in the xeric supralittoral zone, rarely inland; thallus white-pale grey; areoles with marginal folioles | Circinaria leprosescens |
| Not directly on bird perches on seashores; thallus lacking folioles | 16 | |
| 16 (15) | Thallus continuous, rimose-areolate; prothallus grey, visible at edge; cortex C–; widely distributed | Circinaria caesiocinerea |
| Areoles widely scattered, almost globular, on a thin, grey hypothallus; prothallus fimbriate at edge, dark grey-black; cortex C+ white; on flint nodules, rare | Aspicilia tuberculosa |
Classification:
Megasporaceae (All Fungi), Aspicilia (All Fungi), Aspicilia aquatica (All Fungi), Aspicilia cinerea (All Fungi), Aspiciliella intermutans (All Fungi), Aspicilia laevata (All Fungi), Circinaria (All Fungi), Circinaria caesiocinerea (All Fungi), Circinaria calcarea (All Fungi), Circinaria contorta (All Fungi), Circinaria hoffmanniana (All Fungi), Circinaria leprosescens (All Fungi), Lobothallia (All Fungi), Lobothallia melanaspis (All Fungi), Lobothallia recedens (All Fungi), Megaspora (All Fungi), Megaspora verrucosa (All Fungi), Sagedia (All Fungi), Sagedia zonata (All Fungi)