• Porpidia melinodes (Körb.) Gowan & Ahti
Porpidia melinodes
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(Map updated: 11 August 2009)

Those new to lichenology should give Porpidia a wide birth. Very few species can be named in the field despite their often overwhelming abundance. Collections should always include the entire thallus and not just discs or fragments of the thallus chipped casually from an outcrop or boulder. P. melinodes is a sorediate crust with a cracked, orange thallus and iodine negative (I-) medulla which instantly rules out P. tuberculosa, which is the most common, sorediate Porpidia. A small section of the thallus mounted in K will be seen to release scores of extremely tiny ‘oil droplets’ or ‘Fryday bubbles’ so called after their discoverer Alan Fryday. The presence of bubbles is a reliable test for confluentic acid. A section through the disc should reveal a blue-green or olivaceous layer. Look for it on nutrient-poor rocks where there has been some disturbance or mineralization. [Note: thalli with discs may lack soredia]. Northern and western Ireland.

Key characteristics

  • Thallus orange-grey or rust-red, sorediate with medulla I- (If I+blue then Porpidia tuberculosa)
  • K+ numerous tiny ‘oil droplets’ present in thallus section; discs with an olivaceous pigmentation.

Original text submitted by Vince J. Giavarini

 Simms, M. J., (2016). Porpidia melinodes (Körb.) Gowan & Ahti. [In] LichenIreland. Accessed on 2020-07-16.