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Lecideaceae

Family of lichen-forming fungi

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The largest genus in the family, Lecidea, was once a loosely circumscribed wastebasket taxon containing hundreds of morphologically similar species with generally crustose thalli, photobiont-free apothecial margins and translucent, single-celled ascospores. The overall taxonomy and classification within the family has been made more accurate with recent molecular phylogenetics studies. Two Lecideaceae species have been assessed for the global IUCN Red List.

Systematics

Historical taxonomy

The first member of the present-day Lecideaceae to be formally described was Lichen fusco-ater, later known as Lecidea fuscoatra. The Swedish lichenologist Erik Acharius proposed genus Lecidea in 1803, with Lecidea fuscoatra as the type. This was of several dozen lichen species described by the Swedish taxonomist Carl Linnaeus in his influential 1753 treatise Species Plantarum. The family Lecideaceae was originally proposed by the French botanist François Fulgis Chevallier in his 1826 work Flore générale des environs de Paris; his original spelling of the name was Lecideae. Chevallier's short diagnosis of the family included several characteristics emphasising the form and texture of their reproductive structures and crust. He noted their apothecia (fruiting bodies) to be initially somewhat concave, evolving over time into flat or convex forms that resemble small dishes or patellae, each bordered by a distinct margin. This margin may appear similar to or integrated with a crust, which gradually fades as it ages. Chevallier described the crust itself as membranous, varying from smooth to cracked surfaces, and in some instances, spreading out in a soft, powdery (leprose-farinaceous) manner.

In Josef Hafellner's 1984 work Studien in Richtung einer natürlicheren Gliederung der Sammelfamilien Lecanoraceae und Lecideaceae, he used ascus structure as a major systematic character, dividing these two larger families into numerous, smaller families. However, his proposed families (Koerberiellaceae, Lecidomataceae, Mycobilimbiaceae, and Porpidiaceae) have since been folded into Lecidiaceae; later research showed that ascus structure is not a consistent taxonomic character. For example, Buschbom and Mueller showed in 2004 that Porpidiaceae was not monophyletic unless the Lecideaceae was also included, and that the ascus types used to distinguish between the two families turned out to be modifications of the same basic type. This finding was corroborated in 2006 by Miadłikowska and colleagues, who further showed that the family ought to be reclassified from the order Lecanorales to an uncertain (incertae sedis) provisional placement in the subclass Lecanoromycetidae. Early molecular work suggested that the family was monophyletic.

Classification

The conventional classification of lichen-producing fungi has faced challenges due to the reliance on readily observable traits for defining taxonomic groups, which often led to the creation of unnatural groupings of species. An example of this is seen with the genus Lecidea, which by the 1930s, had grown to become one of the largest lichen genera, including around 1200 species. This polyphyletic assemblage of similar-looking species was largely as a result of Alexander Zahlbruckner's multi-volume work Catalogus lichenum universalis, which tended to fit any species with crustose thallus, biatorine or lecideine apothecia and simple ascospores into this wastebasket taxon. However, several studies using morphological and chemical characters demonstrated that Lecidea, in the sense of Zahlbruckner, was polyphyletic. Nearing the end of the twentieth century, researchers had a better idea of the limits of the genus and many taxa were moved to different new and preexisting genera. By 2011, more than 160 genera from various families included species previously classified within Lecidea. In the most recent (2008) edition of the Dictionary of the Fungi, Lecidea was estimated to contain 427 species, although it was acknowledged that only about 100 of these qualified as Lecidea in the strict sense (sensu stricto). In this cases, sensu stricto in the sense of Hertel means saxicolous lichens with certain anatomical characters, such as excipulum, paraphyses and apical ascus structures.

The order Lecideales was proposed by Edvard August Vainio in 1934, in the fourth volume of his work Lichenographica Fennica. The order was generally neglected in later classifications as the family was historically classified in the order Lecanorales. The order was resurrected in 2011 by Schmull and colleagues, who redefined the type genus to include only Lecidea sensu stricto. They used molecular phylogenetics to show that this group of species, defined by morphology and including the type species (Lecidea fuscoatra) and a few Porpidia, species, formed a monophyletic clade. Molecular phylogenetics analysis shows the order Lecideales as a sister group to the Peltigerales.

Etymology

As is standard practice in botanical nomenclature, the name Lecideaceae is based on the name of the type genus, Lecidea, with the ending -aceae indicating the rank of family. The genus name comprises the Greek word λέκος (lékos), meaning "plate" or "small shield", and the suffix "-ídes", indicating similarity. This alludes to the lecideine apothecia, which are usually somewhat circular and lack a thalline margin.

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