''Melanelixia'' is a genus of foliose lichens in the family Parmeliaceae. It contains 15 Northern Hemisphere species that grow on bark or on wood. The genus is characterized by a pored or fenestrate epicortex (a thin homogeneous

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...

layer on the surface of the cortex), and the production of

lecanoric acid Lecanoric acid is a chemical produced by several species of lichen.ubChem - Lecanoric acid"> Lecanoric acid is classified as a polyphenol and a didepside and it functions as an antioxidant. The acid is named after the lichen ''Lecanora''. The acid ...

as the primary chemical constituent of the medulla. ''Melanelixia'' was

circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every po ...

in 2004 as a segregate of the related genus ''

Melanelia ''Melanelia'' is a genus of lichenized fungi in the family Parmeliaceae. The genus was circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The cent ...

''.

Taxonomy

''Melanelixia'' was circumscribed in 2004 as a segregate of the genus ''

''. ''Melanelixia'' originally contained eight species, including the

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * Ty ...

, '' M. glabra''. The genus name combines ''Melanelia'' with the name of lichenologist John A. Elix, "for his immense contributions to lichen systematics and chemistry, especially in Parmeliaceae." Several species distributed in the Southern Hemisphere were removed from ''Melanelixia'' and transferred to the new genus '' Austromelanelixia'' in 2017. This group of species, which forms a distinct

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

in ''Melanelixia'', produces gyrophoric acid rather than lecanoric acid in their medullae.

Description

''Melanelixia'' lichens are foliose and have a loosely to moderately adnate attachment to their substrata. The thallus is made of plane to concave lobes with rounded tips that measure 1–6 mm wide. The upper surface of the thallus ranges in colour from olive-green to dark brown, and has a smooth or wrinkled texture. Features that are variably present on the thallus include maculae (spots or stains), soredia, isidia, and cortical hairs.

Pseudocyphella Pseudocyphellae (singular ''pseudocyphella'') are structures in lichens that appear as tiny pores on the outer surface (the cortex of the lichen. They are caused when there is a break in the cortex of the lichen, and the medullary hyphae extend t ...

e are not present. Cell walls contain the

α-glucan α-Glucans (alpha-glucans) are polysaccharides of D-glucose monomers linked with glycosidic bonds of the alpha form. α-Glucans use cofactors in a cofactor site in order to activate a glucan phosphorylase enzyme. This enzyme causes a reaction t ...

compound

isolichenan Isolichenan, also known as isolichenin, is a cold-water-soluble alpha glucan, α-glucan occurring in certain species of lichens. This lichen product was first isolated as a component of an extract of Cetraria islandica, Iceland moss in 1813, a ...

. The apothecia of ''Melanelixia'' have an abundantly fenestrated or pored epicortex. Ascospores are

ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the ...

to ovoid in shape, thin-walled, and measure 9–15 by 5–11.5

μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

. Lichens in the genus '' Pleurosticita'' are similar in appearance, but are distinguished from ''Melanelixia'' by their broader lobes, pores on the epicortex that are reticulated, a pigment that reacts violet in K and HNO₃, and the presence of depsidones in the medulla.

Habitat and distribution

Found in the Northern Hemisphere, ''Melanelixia'' species grow on bark or wood.

Species

*'' Melanelixia ahtii'' S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016) *'' Melanelixia albertana'' (Ahti) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004) *'' Melanelixia californica'' A.Crespo & Divakar (2010) *'' Melanelixia epilosa'' (J.Steiner) A.Crespo, Divakar, Gasparyan, V.J.Rico, Essl., S.D.Leav. & Lumbsch (2016) *'' Melanelixia fuliginosa'' (Fr. ex Duby) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004) *'' Melanelixia glabra'' (Schaer.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004) *'' Melanelixia glabratula'' (Lamy) Sandler & Arup (2011) *'' Melanelixia glabroides'' (Essl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004) *'' Melanelixia hawksworthii'' S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016) *'' Melanelixia huei'' (Asahina) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004) *'' Melanelixia robertsoniorum'' S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016) *'' Melanelixia subargentifera'' (Nyl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004) *'' Melanelixia subaurifera'' (Nyl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004) *'' Melanelixia subvillosella'' H.Y.Wang & J.C.Wei (2008) – China *'' Melanelixia villosella'' (Essl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)

References

{{Taxonbar, from=Q6811217 Parmeliaceae Lichen genera Lecanorales genera Taxa described in 2004 Taxa named by David Leslie Hawksworth Taxa named by Helge Thorsten Lumbsch Taxa named by Pradeep Kumar Divakar Taxa named by Ana Crespo