• Arthonia zwackhii Sandst.
Arthonia zwackhii
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(Map updated: 11 August 2009)

This species forms white to pale grey, matt thalli among other lichens growing on the dry bark of established trees in wet woodland. It often grows with Phlyctis argena and some authorities believe it may parasitize it. In sallow swamp the brown, thinly frosted, often star-shaped discs form along the edges of bark-expansion cracks so can be hard to see at first. The spores are three- to four-septate with an enlarged upper cell. The longer spores (to 24ųm compared with 16ųm) distinguish it from A. anombrophila. In Ireland, it has only been recorded in Counties Fermanagh and Kerry.

Key characteristics

  • Thallus white or grey, often on the drier parts of trees in wet woodlands; the brown, thinly iced, star-shaped discs grow along bark cracks, in willow especially
  • The C- thallus and large spores separate it from lookalikes.

Original text submitted by Vince J. Giavarini

 Simms, M. J., (2016). Arthonia zwackhii Sandst.. [In] LichenIreland. Accessed on 2019-08-25.