Candelariales

Taxonomy

The yellow "candle-wax" lichens now grouped in Candelariomycetes were long treated as part of the large class Lecanoromycetes. A multigene study of lichen-forming fungi published in 2007 first recognized them as a distinct order, Candelariales – comprising the families Candelariaceae and Pycnoraceae – but still left the group inside Lecanoromycetes. Even earlier, Miądlikowska and co-workers had informally coined the name "Candelariomycetidae" in 2006 for this lineage, but that name was not then validly published under the botanical code. Lücking, Timdal, and Westberg later validly published Candelariomycetidae in 2017 as a new monotypic subclass within Lecanoromycetes, containing the single order Candelariales and its two families, Candelariaceae and Pycnoraceae. They designated Candelariales as the type order and Candelaria as the type genus.

In the circumscription, the subclass was characterized as a group of mostly crustose to squamulose lichens that are often bright yellow, with a green chlorococcoid photobiont and no cephalodia. The group includes species growing on rock, bark, bryophytes, soil, or, in the case of Pycnoraceae, typically on wood. The subclass is difficult to separate morphologically from other lecanoromycete subclasses, apart from the distinctive Candelaria-type ascus with a broad amyloid ring in the lower part of the tholus, it is defined chiefly by molecular phylogenetic evidence rather than by a unique set of outward structural features.

Subsequent DNA analyses that combined ribosomal (nrSSU, nrLSU, mtSSU) and protein-coding (RPB1, RPB2) gene sequences from nearly every recognised class of Leotiomyceta showed that Candelariales never groups with the lecanoroid core. Instead, it forms an isolated, well-supported branch in which Pycnoraceae is placed as the sister family (closest relative) to Candelariaceae. In the best-scoring maximum-likelihood tree the class received 88% bootstrap support (79% under parsimony) and a posterior probability of 1.0, values that molecular systematists regard as strong evidence of a genuine evolutionary grouping.

Recognising this consistent phylogenetic independence, Voglmayr and Jaklitsch erected the new class Candelariomycetes in 2018 (published 2019), with Candelariales as its type order and Candelaria as the nomenclatural type genus. Although different analyses place the class variously near Eurotiomycetes, Arthoniomycetes or Dothideomycetes, none recover it within Lecanoromycetes when a broad taxon sample is used; the lineage is therefore now treated as one of the younger, small classes of filamentous Ascomycota.