''Melanelixia'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

foliose lichen A foliose lichen is a lichen with flat, leaf-like , which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common growth forms of lichens. It typically has distinct upper and lower surfaces, each o ...

s in the family

Parmeliaceae The Parmeliaceae is a large and diverse family of Lecanoromycetes. With over 2700 species in 71 genera, it is the largest family of lichen-forming fungi. The most speciose genera in the family are the well-known groups: '' Xanthoparmelia'' ( 82 ...

. 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 wat ...

layer on the surface of the

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

), 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. It is an ester of orsellinic acid with itself. The acid ...

as the primary chemical constituent of the

medulla Medulla (Latin for "marrow") or medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ...

. ''Melanelixia'' was

circumscribed In geometry, a circumscribed circle for a set of points is a circle passing through each of them. Such a circle is said to ''circumscribe'' the points or a polygon formed from them; such a polygon is said to be ''inscribed'' in the circle. * Circum ...

in 2004 as a segregate of the related genus '' Melanelia''.

Taxonomy

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

, '' 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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

in ''Melanelixia'', produces

gyrophoric acid Gyrophoric acid is a tridepside. It is a double ester of the orsellinic acid. It can also be found in most of the species of the lichen genera '' Actinogyra'', '' Lasallia'', and '' Umbilicaria'' . Natural occurrence and biosynthesis Gyropho ...

rather than lecanoric acid in their medullae.

Description

''Melanelixia'' lichens are

foliose A foliose lichen is a lichen with flat, leaf-like , which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common lichen growth forms, growth forms of lichens. It typically has distinct upper and lo ...

and have a loosely to moderately adnate attachment to their substrata. The

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

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 Soredia are common reproduction, reproductive structures of lichens. Lichens asexual reproduction, reproduce asexually by employing simple fragmentation and production of soredia and isidia. Soredia are powdery propagules composed of fungus, fung ...

isidia An isidium (plural: isidia) is a tiny, wart- or finger-like outgrowth on the thallus surface of certain lichen species. It is one of two principal types of vegetative reproduction, vegetative reproductive structures in lichens, the other being ...

, 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 ...

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 (biochemistry), cofactor site in order to activate a glucan phosphorylase enzyme. This enzy ...

compound

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

. The

apothecia An ascocarp, or ascoma (: ascomata), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. As ...

of ''Melanelixia'' have an abundantly fenestrated or pored epicortex.

Ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...

s are

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

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

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

. Lichens in the genus '' Pleurosticta'' are similar in appearance, but are distinguished from ''Melanelixia'' by their broader lobes, pores on the epicortex that are reticulated, a

pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

that reacts violet in K and HNO₃, and the presence of

depsidone Depsidones (+ " depside" + "one") are chemical compounds that are sometimes found as secondary metabolites in lichens. They are esters that are both depsides and cyclic ethers. An example is norstictic acid Norstictic acid is a depsidone produ ...

s 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