• Megalaria grossa (Pers. ex Nyl.) Hafellner
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Megalaria grossa
© Mike Simms
Megalaria grossa
© Mike Simms
Megalaria grossa
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The large, black, thick-margined, convex discs belonging to this species may resemble those of Bacidia, Lecidea or Cresponea but on the basic-bark of an ash or a maple? Look again. This time you see that the thallus is pale, grey or whitish, non-sorediate, non-isidiate. The discs are large (to 2mm diam.) with shiny raised margins. By a process of elimination you can identify this Megalaria in the field. For further confirmation cut a section through the disc and mount in K. Look at it under a microscope where the large, slightly waisted one-septate spores (20-30 x 8-15ųm) will be seen. Spot tests negative. Western Ireland.

Key characteristics

  • Large, black discs with a thick shiny margin on basic or nutrient-rich bark; thallus neither isidiate or sorediate, pale
  • Mostly in older woodland or large trees in sheltered river valleys.

Original text submitted by Vince J. Giavarini

 Simms, M. J., (2016). Megalaria grossa (Pers. ex Nyl.) Hafellner. [In] LichenIreland. Accessed on 2018-07-17.