Lichen: Arthonia punctiformis
Name: Arthonia punctiformis
Body Type: Crustose
Description: The thallus is immersed in the substrate (identified only by the clear patch it usually creates on the bark). Apothecia are small and vary in shape from round to stellate frequently being elliptical with a hint of stellate (as in the photograph here). Their size may be as small as 0.2mm; they are also black and never prunose (powdery). The edge of the discs may show a lip of bark (as though the bark has been pushed back). Overall the apothecia look like little flecks of black. Spores are colourless, septate (2-celled), oblong or elliptical with a ‘waist’.
Chemical Tests: None. No lichen products detected.
Nature Notes: Common on small twigs and smooth branches of trees and shrubs. It is one of the first lichens to colonise bark. Frequently found with Arthopyrenia punctiformis. Tends to avoid direct sunlight. Confusion: may be similar to Arthonia radiata if the apothecia are stellate (as they tend to be in A. radiata).
Vice county distribution map: See map.
Link: Map this species on the Lichen Survey
Other species recorded in Ireland:
- Arthonia almquistii Vain.
- Arthonia anombrophila Coppins & P.James
- Arthonia arthonioides (Ach.) A.L.Sm.
- Arthonia astroidestera Nyl.
- Arthonia atlantica P.James
- Arthonia cinnabarina (DC.) Wallr.
- Arthonia didyma Körb.
- Arthonia elegans auct.brit.
- Arthonia endlicheri (Garov.) Oxner
- Arthonia epiphyscia Nyl.
- Arthonia excipienda (Nyl.) Leight.
- Arthonia fuscopurpurea (Tul.) R.Sant.
- Arthonia galactites (DC.) Dufour
- Arthonia graphidicola Coppins
- Arthonia ilicina Taylor
- Arthonia ilicinella Nyl.
- Arthonia invadens Coppins
- Arthonia lapidicola (Taylor) Branth & Rostr.
- Arthonia leucopellaea (Ach.) Almq.
- Arthonia mediella Nyl.
- Arthonia muscigena Th.Fr.
- Arthonia phaeobaea (Norman) Norman
- Arthonia pruinata (Pers.) Steud. ex A.L.Sm.
- Arthonia punctella Nyl.
- Arthonia radiata (Pers.) Ach.
- Arthonia spadicea Leight.
- Arthonia stellaris Kremp. 
- Arthonia thelotrematis Coppins
- Arthonia varians (Davies) Nyl.
- Arthonia vinosa Leight.
- Arthonia zwackhii Sandst.
Text and images © Paul Whelan, 2010.