| TAXON: | Megalaria pulverea (Borrer) Hafellner & E. Schreiner (1992) |
| RECENT SYNONYMS: | – |
| FAMILY: | Ramalinaceae |
| GROWTH FORM: | Crustose, homoiomerous (leprose) |
| SUBSTRATES: | Bark of generally acidic, mossy trunks, or rarely branches; sometimes growing over moss; occasionally also mossy rocks or soil, or old Calluna stems |
| PHOTOBIONT: | Dictyochloropsis alga |
| REPRODUCTION: | Soredia; apothecia rare |
| ASCUS: | If present, cylindric-clavate; apex Bacidia– or Biatora-type; (2-)8 spores |
| SPORES: | Ascospores if present fusiform-ellipsoid, 1-septate, 10-16(-19) × 4.5-6.5 µm, thick-walled |
| NOTABLE FEATURES: | Thallus loose, composed mainly of soredia; soredia bluish or greyish or yellowish green, granular, tending to coalesce into continuous granular crust; apothecia when present black, biatorine, with grey and sometimes excluded exciple |
| CHEMICAL TESTS: | Thallus K+ yellow, Pd± yellow-orange-red, K/UV(dry)+ yellow, Pd/UV(dry)+ yellow-orange (atranorin, zeorin, ±fumarprotocetraric acid); where apothecia present, epithecium K+ intensifying green (unknown pigment) |
| HABITAT: | Old Atlantic woodland; indicator of ecological continuity in oceanic, suboceanic and northern boreal woodlands |
| DISTRIBUTION: | Western Britain, particularly western Scotland, Wales and southwest England |
| CONSERVATION STATUS: | Least Concern |
| LICHENICOLOUS FUNGI: | Capronia sp., Merismatium sp., Spirographa fusisporella sens. lat. |
| IDENTIFICATION DIFFICULTY: | Green 2: Field identification possible with care |
| CONFUSION SPECIES: | Megalospora tuberculosa, Phyllopsora rosei |
FIELD NOTES
Megalaria pulverea prefers to colonise mossy trunks in moist Atlantic forest, and it’s a common lichen in such habitat. Indeed, it counts as an indicator of old and ecologically stable woodland. You might find it on patches of bark between moss, or overgrowing the moss itself like a sugary frosting.
Typically, M. pulverea isn’t fertile. It’s made up mostly of soredia: tiny granules of algal cells loosely wrapped in fungal cells, which blow, brush or wash off to form new thalli elsewhere. If M. pulverea does produce fruiting bodies, such as in the unusual specimen below, the apothecia are black, and they have tender-looking grey exciples that are most obvious when young.
Without apothecia, M. pulverea can be confused with other granular crusts that share its habitat, particularly Megalospora tuberculosa and Phyllopsora rosei. But the granules of P. rosei are micro-squamules, not soredia, and more like tiny scales than sugary grains. A close look with a hand-lens should suffice to differentiate between the two species.
Differentiating between M. pulverea and Megalospora tuberculosa takes a bit more care, but it’s not difficult. It’s easiest if apothecia are present: those of M. pulverea are black, while those of Megalospora tuberculosa are chestnut-brown. If apothecia aren’t present, then you’ll need to conduct a quick K-test.
M. pulverea produces atranorin, which reacts K+ yellow, and most tellingly K/UV(dry)+ neon-yellow. Megalospora tuberculosa doesn’t. It’s best to use the K/UV(dry)-test for atranorin because it’s more sensitive, and because Megalospora tuberculosa can give a K+ pale yellow reaction.
M. pulverea also sometimes reacts Pd+ yellow-orange, orange or orange-red due to fumarprotocetraric acid, whereas Megalospora tuberculosa doesn’t. But M. pulverea can lack fumarprotocetraric acid, or produce too little to give a clear result with Pd. By contrast, the K/UV(dry)+ neon-yellow reaction is reliable.
LAB NOTES
Megalaria pulverea can normally be identified without microscopy.
SPECIMENS
Megalaria pulverea : Scotland : VC101 Kintyre : NR7789 : August 2024 : On Alnus trunk
