Taxonomy

The delimitation of the clades A and B on molecular and phenotypic levels is interpreted as indicative at the family level. However, unexpected taxonomic consequences might arise for clade B because it comprises genera of the Caliciaceae, including the type species of the family, C. viride. The similarities of certain phenotypic traits between the Caliciaceae and the Physciacean genera of clade B such as a true excipulum, hypothecium pigmentation, ascospore ornamentation and chemistry as well as their close genetic proximity indicate a closer relation of these taxa than contemporary concepts depict (Tibell 1984, Wedin et al. 2000).

However, the delimitation of clade A from taxa of clade B including the Caliciaceae seems well supported from the presented data. Therefore, the critical question of how Physciaceae and Caliciaceae are related can be restricted to the question of how taxa of clade B are related to the Caliciaceae s. str.. In a phylogenetic survey based on mtSSU and nrITS data, Wedin et al. (2002) showed four members of the Caliciaceae to be paraphyletic with taxa of Clade B. This is confirmed also in this study. However, the phylogenetic positions of those Caliciaceae presented in Wedin et al. (2002) receive little support and appear incongruent with the phylogeny obtained from nrSSU data as presented in this study. Therefore, the phylogenetic relationships between the Caliciaceae and Clade B remains uncertain.

Regarding the type species Calicium viride as the anchor for the positioning of the family, two alternative scenarios might be deduced from the present data: First, the Caliciaceae might form a sister group to Subclade IV and Subclade III might be the sister group to the previous two groups. Clade A being the sister taxon to all of the previous three groups. Second, the Caliciaceae might be nested within Subclade IV.

Therefore, establishing a higher order taxon comprising the taxa of clade B necessarily would also include the Caliciaceae. For reasons of nomenclatorial priority, the establishment of such a taxon would imply the transfer of these taxa into the Caliciaceae. Wedin & Grube (2002) proposed the conservation of the family

Physciaceae Taxonomy

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name Physciaceae against the name Caliciaceae for the complete Physciaceae/ Caliciaceae clade. Although the authors appreciate this attempt, they rather suggest to document the apparent split in the Physciaceae/Caliciaceae clade nomenclatorically. In case a transfer of most Physciaceae species (Clade B comprises more species than Clade A) into the Caliciaceae would be very difficult for most lichenologists to adapt to, it is suggested to conserve the family name Buelliaceae against Caliciaceae for all taxa in Clade B (including the Caliciaceae) and maintain the Physciaceae in a narrower circumscription. However, a "nomen conservandum" is not proposed here and the strict rules of nomenclature are followed.

3.6.1 Emendations

A phenotypic delimitation of the resulting families of the Physciaceae, represented by the taxa of clade A, and Caliciaceae (including the taxa of clade B) could be based on a combination of three characters, of which at least two indicate the correct affiliation. Only Australiaena might still be problematic under this concept, since it has asci that resemble the Lecanora-type ascus and exhibits fairly variable ascospores that occasionally develop ascospore wall thickenings. All other taxa fit the delimitation as given below. The ascospores for both families constantly being pigmented, septate and, with the exception of Rinodinella, thick-walled (see also TABLE 3.4).

3.6.1.1 Caliciaceae Chevall. (1826) emend. G. Helms, G. Rambold & T. Friedl

Asci of Bacidia-type or prototunicate; hypothecium pigmented; ascospores without distinct wall thickenings.

(Species usually with proper excipula, exceptional taxa: see TABLE 3.5.)

3.6.1.2 Physciaceae Zahlbr. (1898) emend. G. Helms, G. Rambold & T. Friedl

Asci of Lecanora-type; hypothecium hyaline; ascospores with distinct wall thickenings or of Rinodinella-type. (Species usually with thalline excipula, exceptional taxa: see TABLE 3.5.)

The interrelations among the taxa of clade B, especially Subclade IV and Caliciaceae Pers. still await a more thorough exploration. A subsequent division of the newly emended Caliciaceae in families, corresponding to Subclades III, IV and the Caliciaceae in their former circumscription, might be appropriate, if further evidence could be found that supports this grouping. The critical taxon that prevents a clear delimitation of the two subclades is Diplotomma. ITS as well as nrSSU sequence data assign this genus to Subclade III, while it seems problematic to consistently delimit this genus from Subclade IV with phenotypic characters.

Accordingly, groupings of taxa assigned to Diplotomma based on nrITS data (this study) and phenotypic traits (Nordin 2000) exhibit incongruencies.

Physciaceae Taxonomy

3.6.1.3 Alternative concepts

A segregation of the Caliciaceae in their new circumscription into three families, as outlined above would form an alternative concept. For Subclades III and IV existing family names could be adopted such as Pyxinaceae (E.M. Fries) Stitzenberger (1862) and Buelliaceae Zahlbr. (1907) respectively. Provided further investigation do not unravel the taxa with prototunicate asci as a polyphyletic assemblage, the Caliciacean concept could be re-established in the actual circumscription. In case the Caliciaceae and Subclade IV intermix, taxa of both groups could be designated to the Caliciaceae, resulting in a tripartite family concept with Physciaceae, Pyxinaceae and Caliciaceae. In all these scenarios, the new concept of the Physciaceae as proposed above would persist.

3.6.2 Conclusions

The Physciaceae are a highly diverse family of lichenized ascomycetes that have experienced detailed taxonomic refinement in the recent past. The nrDNA sequence data support most of the modern genus concepts that were all based on traditional phenotypic characters. It is anticipated that the critical combination of both methods will lead to a better understanding of character and taxa evolution. Although most genera of the Physciaceae were included in this survey, the phylogenetic position of numerous taxa still awaits further investigation.

In order to simplify the presentation and discussion in the following chapters, the distinction between Physciaceae and Caliciaceae as proposed here is not maintained. In the subsequent chapters all species of these two families that were analyzed in this study are denoted as Physciaceae in concordance with traditional usage of this name as well as Wedin & Grube (2002).

Photobionts of the Physciaceae and the genus Trebouxia

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