Generic delimitations in the family Stictidaceae (Ostropales, Ascomycota): the Stictis–Conotrema problem

Abstract

The family Stictidaceae (Ostropales, Ascomycota) contains both lichenized and non-lichenized fungi. Here, we test if Conotrema (lichenized) and Stictis (non-lichenized) as currently delimited are distinct monophyletic genera, by parsimony and parsimony jackknifing analyses of combined nuclear rDNA (ITS and partial LSU rDNA) and mitochondrial SSU rDNA sequence data matrices. The study includes four species of Stictis, three species of Conotrema, and representatives of the related Schizoxylon (lichenized), Odontotrema, Carestiella (at least sometimes associated with algae), Cryptodiscus and Thelotrema (lichenized). In all analyses, the Conotrema species were nested within Stictis with high support. Thus, we conclude that Conotrema are only lichenized representatives of Stictis. The type species of the two generic names, C. urceolatum and S. radiata, are sister taxa in our analyses. Furthermore, the analysis gave no support for the present infrageneric classification of Stictis. Carestiella socia (the type of Carestiella) and the two representatives of Schizoxylon studied were also nested within Stictis s. lat. The Odontotremataceae is the sister group to the Stictidaceae, and Cryptodiscus foveolaris groups with Thelotrema rather than with the Stictidaceae. We conclude that lichenization in the Stictidaceae does not characterize natural groups, and that Conotrema should be considered a synonym to Stictis, as predicted by anatomical characteristics. The new combinations Stictis urceolatum and Stictis populorum are made.