On the nomenclature of lichen phototypes

TLDR: The rather difficult situation arising from the fact that the same fungus, when associating with different photobionts, may form very different-looking lichens, previously named as separate species or even placed in different genera is brought up.

Abstract: Laundon (1995) has brought up for discussion the rather difficult situation arising from the fact that the same fungus, when associating with different photobionts, may form very different-looking lichens, previously named as separate species or even placed in different genera. While I agree that this problem needs to be clarified, I disagree with the solution suggested by Laundon: to classify correlated photobionts as forms of the same species. To me this is not a question of classification, only of nomenclature. It is quite clear that a lichen is classified according to its mycobiont. In mycology there is no tradition to classify, at a specified taxonomic rank, different-looking infections by the same fungus, e.g. different growth forms induced on different hosts. In parasitic fungi there has been a tradition to designate as formae speciales taxa which are characterized by their physiological adaptation to different hosts, being morphologically identical or nearly so, but this is an informal system without nomenclatural status (Code, Art. 4, Note 3). The situation for lichen phototypes is rather similar to and actually parallels that of fungi which show different morphological expressions during their life cycle, and accordingly have been given different names (Jorgensen, 1991), which are acceptable under the dual naming system provided for in Art. 59. Unfortunately the phototypes of lichens are not covered by that Article, not only because it excepts lichens, but because this kind of variation is not expression of a pleomorphic life cycle. I have previously (Jorgensen, 1991) argued that we need a similar system for phototypes, and Greuter (pers. comm.) has suggested that this would find its logical place among the exceptions mentioned in Art. 11.1, referring to names of form-taxa. A formal proposal for the emendation of that Article has not, however, been made, as opinions among lichenologists are rather divided in this respect, as recognized by Laundon (1994). The nomenclatural difficulties in handling this situation are clear from the examples chosen by Laundon (1995). I am sure that both Galloway (1988) and White & James (1988) felt a need to name the two phototypes of one species since they occur separately, having a different ecology and distribution, but they ran into nomenclatural difficulties which were not solved in a satisfactory way. Galloway