In a most interesting paper, Otálora & Wedin (Reference Otálora and Wedin2013) have shown that Collema fasciculare does not belong in the Collemataceae as previously assumed, but in the family Arctomiaceae. Their arguments are convincing, being based both on molecular data and apothecia structure (including ontogeny).
However, the conclusion that this species should provisionally be referred to the genus Arctomia Th. Fr. pending further work is, in my opinion, overly cautious because the morphology and structure of the thallus (for details see Degelius Reference Degelius1954) clearly differ from those of Arctomia, as shown by Henssen (Reference Henssen1969) in her thorough study of that genus. Furthermore, there is also a basic difference in the early stages of the ontogeny between this species and that of Arctomia s. str., as noted by Otálora & Wedin (op. cit.). In Arctomia s. str. the apothecia are always initiated in particular outgrowths of generative tissue, and do not originate within the main thallus as in Collema fasciculare.
The molecular evidence is ambiguous, with Collema fasciculare appearing as sister to the clade containing the generic type, Arctomia delicatula Th. Fr., making it possible to recognize C. fasciculare in a distinct genus. Otálora & Wedin (op. cit.) rejected this option because they did not wish to erect a new genus that would possibly be reduced to synonymy when relationships within the family were further resolved. However, I prefer this option because of the differences in anatomy and apothecial ontogeny referred to above, and because there is already an available generic name to accommodate Collema fasciculare that would, in fact, be a threat to Arctomia if the taxonomy preferred by Otálora & Wedin (op. cit.) is followed. This generic name, Gabura, was already established with a clear diagnosis in Reference Adanson1763 by Adanson to accommodate “Lichenoides, Dill. Musc. T. 19, f.27”, which, as noted by Degelius (op.cit.), is none other than Collema fasciculare.
The correct name for this species is accordingly:
Gabura fasciculare (L.) P. M. Jørg. comb. nov.
MycoBank No.: MB808077
Lichen fascicularis L., Mantissa I:133 (1767); type: Sweden, Småland, Stenbrohult, C. Linné fil. (LINN 1273, lectotype by Degelius Reference Degelius1954, see Jørgensen et al. Reference Jørgensen, James and Jarvis1994).
This name will be the correct one for this species whatever taxonomic view is taken on the generic structure, unless Arctomia is conserved over it. That would be a premature procedure at the moment, when the generic taxonomy has not been fully clarified and further taxa need to be considered in the molecular analysis and carefully compared with the morphological characters.
