• Porpidia contraponenda (Arnold) Knoph & Hertel
Porpidia contraponenda
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These thick white crusts which decorate siliceous rocks in the uplands require a great deal of attention and often, laboratory analyses. What draws the observer to this species is the chalky-white purity of the thallus and minutely warted surface. Discs are common, never immersed, margin raised and exciple black. All reactions are negative.

Key characteristics

  • Stunning, chalky-white crusts (often several cms diam.), surface minutely warted and with scattered, sessile (not sunken) discs
  • Disc edges raised and exciple black; reactions negative; on siliceous rock.

Original text submitted by Vince J. Giavarini

 Simms, M. J., (2016). Porpidia contraponenda (Arnold) Knoph & Hertel. [In] LichenIreland. Accessed on 2018-08-14.