Melanelixia fuliginosa is a species of foliose lichen in the family Parmeliaceae, commonly found growing on siliceous rocks in humid, temperate regions of Europe and possibly parts of Asia. It forms dark brown to blackish rosettes up to 15 cm in diameter with small overlapping lobes that bear numerous tiny, cylindrical outgrowths (isidia) on their surface. The lichen primarily reproduces by vegetative means when these isidia break off and establish new colonies. Originally described by French botanist Jean Étienne Duby in 1830 as a variety of another lichen, it has undergone several taxonomic changes, being assigned to various genera including Parmelia and Melanelia before its current classification in Melanelixia in 2004. Although historically thought to occur in North America, recent studies suggest true M. fuliginosa may be restricted to Europe, with North American specimens now identified as the closely related Melanelixia glabratula, which prefers bark rather than rock substrates.
Taxonomy Melanelixia fuliginosa was originally described by the French botanist Jean Étienne Duby in 1830 (attributed to Elias Fries) as Parmelia olivacea var. fuliginosa, a variety of another lichen. Duby's protologue placed the taxon as varietas γ of Parmelia olivacea, characterising var. fuliginosa as having a thallus thallo punctis elevatis fuliginosis confertissimis adsperso — 'densely sprinkled with sooty, raised punctae' — and citing specimens gathered on siliceous cliffs near Bernay and Vire in Normandy, France. In 1870, the lichen was raised to species rank by Arnold under the name Imbricaria fuliginosa. Later authors recombined it into the large genus Parmelia: e.g. as Parmelia fuliginosa in the 19th century. During the 20th century, there was some confusion with an unrelated species Sticta fuliginosa that had a similar epithet; to avoid this, Parmelia fuliginosa (Fr. ex Duby) was sometimes cited with "non (Ach.) Schaer." to distinguish it from Acharius's Sticta name. By the late 1900s, P. fuliginosa was included in a subgroup of brown Parmelia lichens. Ted Esslinger segregated these into the genus Melanelia in the 1970s, and he formally transferred this species to Melanelia fuliginosa in 1987. Some authorities during that time treated fuliginosa as not a distinct species but rather part of a species complex: Jack Laundon considered it a subspecies of Parmelia glabratula, naming it Parmelia glabratula subsp. fuliginosa. Thus, older British literature sometimes refers to P. glabratula subsp. fuliginosa for saxicolous (rock-dwelling) specimens. There was long-standing debate over whether the dark, rock-dwelling form and the paler, bark-dwelling form represented one species or two. This was resolved by a molecular phylogenetics study in 2011, which showed two well-supported lineages. As a result, the bark-dwelling taxon was separated and elevated to Melanelixia glabratula in 2011, while M. fuliginosa was retained for the darker saxicolous species. Melanelixia glabratula was originally described by Pierre Lamy (1878) as Parmelia fuliginosa subsp. glabratula, and is now recognized as a distinct species closely related to M. fuliginosa. In the broader classification, Melanelixia fuliginosa belongs to the parmelioid lichens, a clade of foliose lichens in the large Parmeliaceae. The delimitation of Parmelia sensu lato (in the wide sense) was controversial in the late 20th century: some lichenologists split it into many smaller genera based on thallus colour and morphology (e.g. Hale 1974; Elix 1994), while others preferred a broad Parmelia (e.g. Purvis et al. 1992). Molecular studies ended this debate, supporting the separation of distinct genera. In 2004, the genus Melanelixia was established for a clade of the "brown Parmelia" group, including M. fuliginosa and its allies. The new genus was distinguished from the residual Melanelia and the related genus Melanohalea on molecular and morphological grounds. Since 2004, the accepted name of this species has been Melanelixia fuliginosa, with Melanelia fuliginosa and Parmelia fuliginosa as well-known synonyms.
Description
The lichen forms a foliose (leaf-like) thallus in rosettes up to about 10–15 cm in diameter. The individual lobes are small (typically 1–4 mm wide), contiguous to overlapping, with rounded tips that may be slightly upturned. The upper surface is greenish-brown when wet, drying to dark brown or blackish in strong light, and is usually smooth to faintly wrinkled and shiny (especially near the lobe ends). The lobe margins and surfaces bear abundant isidia – tiny cylindrical outgrowths of the thallus. These isidia are often branched and coralloid in form, and can detach easily; when they break off they leave behind distinct white scars or pits on the cortex. The lower surface of the thallus is black to dark brown, with a paler brown margin, and has simple, mostly unbranched rhizines (root-like attachments) up to about 1 mm long that anchor the lichen to its substrate. The thallus is heteromerous (with a distinct algal layer) and contains a green chlorococcoid photobiont (algal partner) in the upper cortex. Reproduction in M. fuliginosa is primarily vegetative by dispersal of isidia, which can break off and establish new colonies. Sexual reproduction is uncommon – many thalli lack fruiting bodies. When present, the apothecia are small disk-like structures up to 5–6 mm across. The apothecia are lecanorine, meaning they have a rim of thallus tissue; in this species the apothecial margin is often adorned with isidia as well. The apothecial disk is usually concave to flat, dark red-brown to black, and without perforations. Inside the apothecia, the asci contain eight ascospores of the usual one-celled type for Parmeliaceae. The ascospores are hyaline (colourless), ellipsoid, and measure roughly 10–14 × 5–8 μm. The asci themselves have a blue amyloid inner layer in iodine (Lecanora-type asci). Pycnidia (asexual conidiomata) are rare on M. fuliginosa; when present they appear as tiny immersed black dots and produce conidia that are bacilliform (rod-shaped), and about 6–8 × 1 μm in size. The conidia often have slightly swollen ends and are released to serve as another means of propagation (analogous to fungal "spores").
… excerpt ends here. Continue reading the full article.
