Melaspilea


Melaspilea is a genus of fungi in the family Melaspileaceae. The genus includes both lichen-forming species that grow on tree bark and lichenicolous species that parasitise other lichens. Originally, Melaspilea encompassed a broad and diverse group of species, but a 2015 molecular study narrowed its circumscription, showing that many species historically placed in the genus actually belonged to unrelated lineages. In its current sense, Melaspilea belongs to the family Melaspileaceae and order Eremithallales within Dothideomycetes and is characterised by dark fruiting bodies with single-septum spores. The genus has a worldwide distribution but is particularly diverse in tropical regions, with species primarily found growing on the bark of trees and woody plants.

Taxonomy

The genus was established by the Finnish lichenologist William Nylander in 1857. In his original description, Nylander characterized Melaspilea as having a thin or inconspicuous thallus and a black apothecium with a superficial or simple that is often convex. The genus was distinguished by its discrete paraphyses, ovoid to somewhat uncoloured single septum spores measuring 8 micrometres, and lack of a hymenial gelatin. The type species, M. arthonioides, was described from specimens collected on ash trees near Philippeville, Algeria. Nylander noted that while the species was rare in France, particularly on elm trees, it was not truly found there in a well-developed state. He also described a second species, M. deformis, characterized by its reduced thallus, small or medium-sized rounded or deformed apothecium, and occurrence on oak, walnut, and ash trees in Switzerland.
For much of its history, names placed in Melaspilea formed a heterogeneous assemblage with uncertain rank and placement; different authors treated parts of the group in Arthoniomycetes, Graphidales, Patellariaceae and Buelliaceae, or as lichenicolous outliers, reflecting the lack of a stable circumscription.
A multi-locus phylogenetic study in 2015 dismantled the broad, traditional concept of the genus and family. It showed that Melaspilea is polyphyletic: Melaspilea in the strict sense belongs in the order Eremithallales within Dothideomycetes, together with the rock-dwelling genus Encephalographa; Eremithallaceae is treated as a synonym of Melaspileaceae. In the same work, the authors subsumed Eremithallus into Melaspilea and made the new combinations Melaspilea costaricensis, Melaspilea enteroleuca and Melaspilea urceolata. Many other species historically assigned to Melaspilea were shown to belong in Asterinales and are best treated in segregate genera such as Melaspileella, Melaspileopsis and Stictographa. The revised framework reflects that superficially similar dark, 1-septate ascomata have evolved repeatedly in unrelated lineages, and that lichenised and lichenicolous lifestyles are intermingled within Asterinales.

Description

Melaspilea forms a thin, whitish, bark-inhabiting thallus with a green-algal partner. The ascomata are usually rounded to short-, immersed at first, then and finally superficial, with a flat to slightly convex disc bordered by a low, sometimes lobulate margin. The is dark reddish-brown and turns olive-brown with potassium hydroxide solution. The hymenium is non-amyloid.
Asci are elongate to somewhat cylindrical with a thickened apex and a distinct, each typically containing eight 1-septate ascospores. The spores are ellipsoid, smooth, hyaline when young and brown at maturity, and commonly constricted at the septum. In some material a gelatinous sheath becomes blue after KOH pretreatment followed by iodine, but the taxonomic weight of this sheath is uncertain. Filamentous paraphyses are to branched and not markedly swollen at the tips. Reports of cell clusters within bark cells connected to the apothecia by hyaline hyphae pertain to Central American material formerly segregated as Eremithallus and are not considered diagnostic for the genus as currently circumscribed.

Habitat, distribution, and ecology

Species of Melaspilea are primarily corticolous, meaning they grow on the bark of trees and woody plants. The genus has a worldwide distribution but appears more diverse in tropical regions, though it is also well-represented in temperate areas. For example, eleven species have been accepted in the lichen flora of Great Britain and Ireland. M. enteroleuca is consistently corticolous on old trees and has records across much of Europe, with reports in North Africa and Asia; by contrast, M. urceolata is American. M. costaricensis is confirmed from Costa Rica and Saba.

Species

, Species Fungorum accept 59 species of Melaspilea. Many names historically placed in Melaspilea have been shown to belong in Asterinales rather than Melaspilea in the strict sense.