| Melaspilea | |
|---|---|
 | |
| Melaspilea ochrothalamia , found in Sintra, Portugal | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Dothideomycetes |
| Order: | Eremithallales |
| Family: | Melaspileaceae |
| Genus: | Melaspilea Nyl. (1857) |
| Type species | |
| Melaspilea arthonioides (A.Massal.) Nyl. (1857) | |
| Synonyms [1] | |
Melaspilea is a genus of lichen-forming and lichenicolous fungi in the family Melaspileaceae. [2]
The genus was circumscribed by the Finnish lichenologist William Nylander in 1857. The taxonomy of the genus has undergone significant revision based on molecular phylogenetics studies. Historically, Melaspilea was considered a heterogeneous assemblage of fungi with uncertain taxonomic placement. The genus was provisionally placed in the class Arthoniomycetes, but had also been included in various higher-level groups such as Graphidales, Patellariaceae, and Buelliaceae by different researchers. [3]
Modern molecular studies have shown that Melaspilea is polyphyletic, meaning that species traditionally placed in this genus actually belong to two main evolutionary lineages within the Dothideomycetes: [3]
The genus Encephalographa, once considered separate, is also placed in Melaspileaceae based on molecular evidence, despite morphological differences from Melaspilea in its branched, anastomosed ascomata with a longitudinal opening. [3]
This taxonomic revision better reflects the evolutionary relationships among these fungi and demonstrates that fungi with similar morphological features (such as dark ascomata and 1-septate brown ascospores) have evolved independently in different lineages. The revision also shows that within the Asterinales, lichenicolous and saprobic lifestyles appear intermixed in the phylogenetic tree, suggesting multiple evolutionary transitions between these ecological strategies. [3]
Melaspilea (in the strict sense) is characterized by its thin, white, bark-inhabiting thallus (fungal body) that forms a symbiotic relationship with green algae of the genus Trentepohlia. The reproductive structures (ascomata) are typically rounded, initially developing beneath the bark surface (immersed) but later becoming exposed (erumpent) and eventually superficial. These structures have a flat to slightly convex disc-like surface with a slightly raised margin, often surrounded by fragments of the substrate. [3]
The protective outer layer (exciple) of the ascomata is reddish-brown, turning olive-brown when treated with potassium hydroxide (K+). The hymenium (spore-producing layer) does not turn blue when treated with iodine (non-amyloid). The ascomata contain thread-like structures called paraphyses, which may be branched or connected to each other. Special protective filaments called periphyses arise from the inner layer of the exciple. [3]
The spore-producing cells (asci) are elongated club-shaped to almost cylindrical, each containing eight spores. The ascus wall is thickened at the top and has a distinct chamber-like structure (ocular chamber), which does not react with iodine (I- and K/I-). The ascospores are ellipsoid in shape and divided by a single septum (cross-wall), appearing smooth and ranging from colorless (hyaline) when young to brown when mature. The spores are typically constricted near the septum and may be surrounded by a gelatinous sheath that turns blue when treated with iodine following potassium hydroxide pretreatment (K/I+ blue). [3]
Species formerly placed in Melaspilea but now assigned to other genera may differ from this description, particularly in their growth habit (lichenicolous versus lichenized), ascomata shape (elongated versus rounded), and the structure of their exciple (continuous below the hymenium versus not). [3]
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. [3]
