# Morphological variation and genetic diversity of Circinaria contorta (Megasporaceae, Ascomycota), including C. contorta subsp. albida subsp. nov

## TL;DR

This study explores the genetic and morphological diversity of the lichen Circinaria contorta, identifying a new subspecies and clarifying its taxonomy.

## Contribution

The paper introduces a new subspecies, Circinaria contorta subsp. albida, and provides a clearer taxonomic framework for C. contorta.

## Key findings

- Circinaria contorta specimens form multiple clades, indicating challenges in species identification.
- A new subspecies, C. contorta subsp. albida, is described based on genetic and morphological data.
- An epitype specimen is designated for C. contorta subsp. contorta to clarify its species concept.

## Abstract

Circinaria contorta is a widely distributed, crustose, saxicolous lichen, which thallus is composed of olive-brown, white pruinose areoles and crater-like apothecia. Although it is one of the more common taxa occurring on limestone substrata in Europe and a generic type species, no type specimen has ever been designated for this species, and there are only a very few studies concerning this taxon. During research on C. contorta in Poland, tree main phenotypes (groups A, B and C) were delineated within the sampled material. Molecular analyses of sequences of the genus Circinaria from worldwide sampling indicated that representatives of C. contorta did not form one clade but rather were distributed at different points within the phylogenetic tree, probably due to difficulties in the correct identification of this species. Analyses based on three molecular markers, namely nucITS rDNA, MCM7, and mtSSU rDNA sequences, showed that specimens representing the phenotypic groups A and C were intermixed on the phylogenetic tree within the C. contorta group. However, the specimens from group B formed a separate, well-supported clade and are described herein as a new taxon at subspecies rank, Circinaria contorta subsp. albida. Specimens of group C had phenotypic features similar to those of Circinaria hoffmanniana, suggesting that the taxonomic concept of this species needs clarification. Furthermore, the species concept of Circinaria contorta subsp. contorta has been specified by designating an epitype specimen collected in Germany. This specimen belonged to phenotypic group A and contained aspicilin as a secondary metabolite.

The online version contains supplementary material available at 10.1038/s41598-025-04627-8.