Lecideaceae
The Lecideaceae are a family of lichen-forming fungi in the order Lecideales. It contains about 30 genera and roughly 250 species. A major distinguishing characteristic of the family is the form of the fruiting bodies: typically circular, dark, and without a. Most species in the family are lichenised with green algae, although a few species, scattered amongst several genera, are lichenicolous—they live on other lichens. Lecideaceae lichens tend to grow on rocks, wood, and soil. Several Lecideaceae species accelerate the weathering of rock surfaces, a process known as pedogenesis, by extending their hyphae into cracks and expelling rock flakes. This contributes to significantly faster weathering rates in certain environments, impacts various materials from natural rocks to man-made Sekishu roof tiles, and involves key biomolecules identified for survival and biodeterioration, including compounds to withstand intense ultraviolet radiation.
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 of the family included several characteristics emphasising the form and texture of their reproductive structures and crust. He noted their apothecia 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 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, dividing these two larger families into numerous, smaller families. However, his proposed families 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 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 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. 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 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 indicating the rank of family. The genus name comprises the Greek word λέκος, meaning "plate" or "small shield", and the suffix "-ídes", indicating similarity. This alludes to the apothecia, which are usually somewhat circular and lack a thalline margin.Description
Family Lecideaceae comprises lichens with a range of growth forms from crust-like to scale-like. In rare instances, the thallus may be absent. These organisms establish a symbiotic relationship primarily with green algae, and in some instances, they also engage with cyanobacteria within specialised structures called cephalodia. The reproductive structures of these lichens are typically apothecia, which can either sit prominently on the surface or be partially embedded within the thallus. These apothecia may resemble those found in the genera Lecidea and Aspicilia. Most genera in Lecideaceae have lecideine apothecia; exceptions are Bellemerea, Koerberiella, and Lecaimmeria, which have lecanorine apothecia. The structure and position of the ascocarp in Cyclohymenia epilithica appear to be unique among Lecideaceae: this lichen has a central sterile column surrounded by a ring-shaped hymenium.File:Lecidea uniformis.jpg|thumb|upright=1.2|right|Microscopy of cross section of K/I-stained Lecidea uniformis apothecium, showing a , hymenium with asci and paraphyses, , and a thin, light-coloured band of between them
The internal framework of these reproductive structures is made up of paraphyses, which are sparingly branched and interconnected. These structures are amyloid, and stain blue with iodine. Paraphyses are usually swollen at the tips, and often pigmented. The asci, or spore-bearing cells, are partially split and feature an amyloid structure at the tip and amyloid walls, housing a pale central area and a darker top or ring-like structure. These asci are club-shaped to cylindrical.
Lecideaceae lichens typically produce eight spores per ascus. These are non-septate, cylindrical to ellipsoid in shape, hyaline, and non-amyoid. The conidiomata of Lecideaceae are in the form of ; these structures tend to be dark-walled and immersed in the thallus. The conidia are non-septate and can be cylindrical, rod-shaped, or thread-like.
Identifying species within the largest Lecideaceae genus, Lecidea, is challenging due to similarities in morphology, anatomical structures, and chemical compositions with many other genera, especially Lecidella in the family Lecanoraceae, and Porpidia in the Lecideaceae. The main distinctions between Lecidea and Lecidella include Lecidellas typically grey, granular thallus with black, blue-black, or white-grey lower thallus; reproductive structures such as soredia, isidia, and blastidia; common presence of conidiomata; Lecanora-type asci; paraphyses that are not fused and easily dispersed; and secondary metabolites including xanthones, orcinol depsidones, β-orcinol depsides, and triterpenoids. Lecidea and Porpidia, both belonging to the Lecideaceae, differ in that Porpidia has soredia, isidia, and blastidia; conidiomata; Porpidia-type asci apex; spores with a halo; fused and branched paraphyses; and secondary metabolites like confluentic acid, norstictic acid, hypostictic acid, 2'-O-methylmicrophyllinnic acid, and 2'-O-methylperlatolic acid. Due to the subtle morphological differences among these genera, distinguishing them based solely on morphology and chemical components is difficult.