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 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 — — 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 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 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 (with a distinct ) and contains a green 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 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 (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").
Chemistry.
Like many parmelioid lichens, "Melanelixia fuliginosa" produces several secondary metabolites (lichen products) in its tissues. The medulla contains lecanoric acid and 5‑methoxylecanoric acid as major substances. These are orcinol-type depsides that can be detected by standard chemical spot tests: a medulla scraping is C+ (red) and also KC+ (red). The medulla is usually K–, but if an orange pigment is present in the lower medulla, a K test produces a purple-violet colour. This reaction is caused by an anthraquinone pigment, likely rhodophyscin (or a related anthraquinone such as skyrin), which occurs as a minor compound in some specimens. Other spot tests are negative (P–, UV–), indicating the absence of lichen substances like depsidones or usnic acid. Thin-layer chromatography has been used to confirm the chemical profile of "M. fuliginosa", revealing the above compounds and occasionally unidentified minor substances.
Habitat and distribution.
"Melanelixia fuliginosa" is chiefly a saxicolous lichen – it grows on rock. It shows a preference for siliceous (acidic) rocks such as granite, sandstone, and other acidic outcrops. Typical habitats include boulders, rocky cliffs, scree, and stone walls in moorland or montane areas, especially in regions with clean air and ample rainfall. In these settings it can form extensive dark brown patches on rock faces, often alongside other acid-rock lichens. The species is described as mainly silicicolous (occurring on silica-rich rock). It is usually found in semi-exposed to well-lit conditions; too much deep shade inhibits its growth, while full sun can cause the thallus to become very dark and compact. Although primarily found on rock, "M. fuliginosa" has occasionally been recorded on the bark of trees or on old wood (such as fence posts or dead trunks). Such corticolous (bark-growing) occurrences are more common in humid, coastal or montane woodlands. However, many bark populations historically identified as "M. fuliginosa" have turned out to be "Melanelixia glabratula", which favours bark and has a slightly different appearance.
In terms of geography, "Melanelixia fuliginosa" has a broad Northern Hemisphere distribution. In the wide sense (before separation of "M. glabratula"), it was regarded as an almost circumpolar species, found across Europe, Asia, and North America in temperate to boreal zones. It occurs on both bark and rock in its range, favouring fairly humid climates and acidic substrates. "M. fuliginosa" is widespread in Europe, where it is especially frequent in northern and western regions. For example, it is common in the British Isles (particularly Scotland, Ireland and western England/Wales) on siliceous rocks, and in Fennoscandia and the Alps. Its European range extends from subarctic areas in Scandinavia and Russia down to mountainous parts of southern Europe (e.g. the Pyrenees, Italian Alps, and Balkan mountains), though it is less common in dry lowland Mediterranean areas. In Asia, the species (in a broad sense) has been reported in temperate parts of Russia, East Asia, and Central Asia – for instance, in Siberia and high elevations of Korea and Japan (often on rock outcrops in cool climates). Some records also exist from North Africa (e.g. Atlas Mountains) and other outlying regions.
Reports of "M. fuliginosa" from North America have undergone re-evaluation. It was historically cited from both western North America (the Pacific Northwest, Rocky Mountains) and eastern North America (New England and the Appalachians), usually on siliceous rocks in upland areas. These populations were long assumed to be the same species as the European "M. fuliginosa". Recent molecular and taxonomic studies, however, indicate that true "Melanelixia fuliginosa" may be absent from North America. Esslinger noted that North American reports of "Melanelia"/"Melanelixia fuliginosa" were misidentifications of "M. glabratula" or other look-alikes. In light of this, North American lichen checklists now exclude "M. fuliginosa" in the strict sense, treating the prevalent camouflage lichens on rocks as "M. glabratula" or related species.
Ecologically, "Melanelixia fuliginosa" tends to be an indicator of relatively unpolluted, acidic environments. It tolerates cold and wet conditions well, and can be found from sea level (on coastal rocks) up to alpine zones (on exposed summits) as long as the substrate is suitable. In areas where it occurs, it contributes to rock surface communities and provides microhabitats for small invertebrates. It is not considered endangered. In the UK, for example, it is rated of Least Concern due to its broad distribution and commonality. However, distinguishing it from "M. glabratula" in the field requires attention to substrate and subtle morphological differences.