• Source: Myelochroa

Myelochroa is a genus of foliose lichens in the family Parmeliaceae. They are commonly known as axil-bristle lichens. It was created in 1987 to contain species formerly placed in genus Parmelina that had a yellow-orange medulla due to the presence of secalonic acids. Characteristics of the genus include tightly attached thalli with narrow lobes, cilia on the axils, and a rhizinate black lower surface. Chemical characteristics are the production of zeorin and related triterpenoids in the medulla. Myelochroa contains about 30 species, most of which grow on bark. The genus has centres of distribution in Asia and North America.




Taxonomy


Myelochroa was originally circumscribed by Yasuhiko Asahina as a subsection of section Hypotrachyna in genus Parmelia. This taxon was later raised to sectional status by Hale in 1976. It was promoted to generic status in 1987 by John Elix and Mason Hale. Nineteen species were originally placed in Myelochroa, including the type species, M. aurulenta.
Myelochroa species are commonly known as "axil-bristle lichens".




Description


Myelochroa lichens are small- to medium-sized foliose lichens. Their thalli comprises somewhat linear to irregularly shaped lobes. The lobes have simple (unbranched), slender, black cilia on the margin, sparsely or densely distributed. These are sometimes confined to lobe axils, other times they are more evenly distributed. The upper surface of the thallus is grey, or blue-grey, sometimes with a yellow tinge; this yellowish colour, if present, is more likely to be under the apothecia or close to the algal layer. The medulla is yellow-orange. The lower thallus surface is black and covered with mostly unbranched rhizines. The apothecia are lecanorine, with a reddish-brown cup that lacks perforations. The ascospores, which number eight per ascus, are simple, ellipsoid, colourless, and measure 5–8 by 8–14 μm.
The upper cortex contains the lichen acids atranorin, chloroatranorin, and secalonic acid. The medulla contains hopane triterpene compounds such as zeorin and leucotylic acid as well as secalonic acid A. The presence of these triterpenes distinguishes this genus from Parmelina, and its segregate genera, including Parmelinella, and Parmelinopsis. secalonic acid A is a yellow pigment that reacts C+ yellow and K+ yellow with lichen spot tests.




Habitat and distribution


Most Myelochroa lichens are corticolous. They are largely found in temperate locations, with centre of distribution in eastern Asia and eastern North America. Twelve species of Myelochroa are found in South Korea. The type species, Myelochroa aurulenta, is found throughout the world in temperate forests.




Species



Myelochroa amagiensis (Asahina) Elix & Hale (1987)
Myelochroa aurulenta (Tuck.) Elix & Hale (1987) – widespread
Myelochroa coreana Y.S.Park (1990) – South Korea; Malaysia
Myelochroa crassata (Hale) Elix & Hale (1987)
Myelochroa crenulata (J.C.Wei) Hale ex DePriest & B.W.Hale (1998)
Myelochroa degelii (Hale) Elix & Hale (1987)
Myelochroa denegans (Nyl.) Elix & Hale (1987) – Asia; Australia
Myelochroa entotheiochroa (Hue) Elix & Hale (1987) – Asia
Myelochroa galbina (Ach.) Elix & Hale (1987) – Asia; North America
Myelochroa hayachinensis (Kurok.) Elix & Hale (1987) – Jeju Island
Myelochroa ibukiensis K.H.Moon, Kashiw. & Keis. Kobay. (2013) – Japan
Myelochroa immiscens (Nyl.) Elix & Hale (1987)
Myelochroa indica (Hale) Elix & Hale (1987) – India
Myelochroa irrugans (Nyl.) Elix & Hale (1987) – Asia
Myelochroa leucotyliza (Nyl.) Elix & Hale (1987) – Asia
Myelochroa macrogalbinica Divakar, Upreti & Elix (2001) – India
Myelochroa metarevoluta (Asahina) Elix & Hale (1987) – Asia; USA
Myelochroa nothofagi Elix (1996)
Myelochroa obsessa (Ach.) Elix & Hale (1987)
Myelochroa perisidians (Nyl.) Elix & Hale (1987) – Asia
Myelochroa radiculata (Kurok.) Divakar & A.Crespo (2010)
Myelochroa rhytidodes (Hale) Elix & Hale (1987)
Myelochroa salazinica Sheng L.Wang, J.B.Chen & Elix (2001) – China
Myelochroa sayanensis Otnyukova, Stepanov & Elix (2009) – Siberia
Myelochroa siamea Kurok. (1998) – Thailand
Myelochroa sibirica Otnyukova, Stepanov & Elix (2009) – Siberia
Myelochroa sikkimensis Divakar, Upreti, G.P.Sinha & Elix (2001) – India
Myelochroa sinica Sheng L.Wang, J.B.Chen & Elix (2001) – China
Myelochroa subaurulenta (Nyl.) Elix & Hale (1987)
Myelochroa supraflava Canêz & Marcelli (2008) – Brazil
Myelochroa upretii Divakar & Elix (2001) – India
Myelochroa xantholepis (Mont. & Bosch) Elix & Hale (1987) – Asia
The taxon once known as Myelochroa lindmanii (Lynge) Elix & Hale (1987) has been analysed molecularly and shown to belong to the genus Parmelinella.




References

Kata Kunci Pencarian:

• Myelochroa
• Myelochroa salazinica
• Canoparmelia cassa
• Canoparmelia albomaculata
• Outline of lichens
• Parmotremopsis
• Parmelinella
• Dalip Kumar Upreti
• Parmeliaceae
• List of lichens of Soldiers Delight