Melanohalea

Melanohalea was circumscribed in 2004 by lichenologists Oscar Blanco, Ana Crespo, Pradeep K. Divakar, Theodore Esslinger, David L. Hawksworth and H. Thorsten Lumbsch. A segregate of the genus Melanelia, Melanohalea originally contained 19 species, including the type, M. exasperata. The species transferred to Melanohalea were formerly included in section Vainioellae of genus Melanelia. This section, in turn, was derived from Parmelia subgenus Euparmelia sect. Vainioellae, originally proposed by Vilmos Gyelnik in 1932. Section Vainioellae included "brown parmelioids" with broad lobes that are round to rather elongate and more or less flat.[1] The "brown parmelioids" refers to Parmelia species lacking atranorin or usnic acid in the cortex, but having a dark to medium-brown thallus colour.[2] Modern molecular phylogenetic analysis has shown that genus Melanohalea is part of the "Melanohalea" clade, a lineage that includes most of the other "brown parmelioids". Other genera in this clade are Emodomelanelia, Melanelixia, Montanelia, and Pleurosticta.[3]

The genus name combines Melanelia with the name of lichenologist Mason Hale, who, according to the authors, "provided the foundations for subsequent contributions to our knowledge of this family".[2]

Methods used to estimate the evolutionary divergence of taxa, including the multispecies coalescent process, suggest that most diversification of Melanohalea occurred throughout the Miocene (23.03 to 5.333 BP) and Pliocene (5.333 million to 2.58 BP), and divergence estimates suggest that diversification that occurred during the glacial cycles of the Pleistocene was not accompanied by speciation in Melanohalea.[4]

Closeup of apothecium of herbarium specimen of Melanohalea olivacea showing white pseudocyphellae on the margin

Melanohalea lichens have a foliose thallus that is loosely to moderately attached to its substrate. The lobes comprising the thallus are flat to concave with rounded tips, lack cilia, and measure 0.5–7 mm wide. The upper surface of the thallus is olive-green to dark brown, ranging in texture from smooth to wrinkled, and lacks spots or stains. It is usually features pseudocyphellae on warts or on the tips of isidia; the presence of soredia and isidia is variable. The upper cortex is paraplectenchymatous (a cell arrangement where the hyphae are oriented in all directions), and measures 10–16 mm thick. The epicortex does not have pores, unlike the related genus Melanelixia. Cell walls contain the α-glucan compound isolichenan. The medulla is white and has a smooth and flat lower surface that is coloured pale brown to black. Rhizines are simple (i.e. unbranched).[2]

The ascomata are apothecial, laminal (arranged in plates), sessile to more or less pedicellate. The apothecial disc is brown, and is not perforated. It is initially concave but becomes convex with age. The amphithecium (a layer of cells that surrounds the apothecium) has pseudocyphellate papillae, without spots or stains. Asci are elongated, club-shaped (clavate), Lecanora-type, and thickened at the tip. They lack an internal apical beak, and have between 8 and 32 spores. Ascospores of Melanohalea are spherical to ovoid or ellipsoid in shape, thin-walled, colourless, and measure 5.5–20 by 4–12.5 μm. The conidiomata are pycnidial, immersed, and laminal. The shape of the conidia ranges from cylindrical to fusiform (spindle-shaped); they are simple, colourless, and measure 5–8.5 by 1 μm long.[2]

The cortex of Melanohalea lichens have a brown pigment, but lack other compounds. The medulla contains depsidones (including fumarprotocetraric acid and norstictic acid) or lack secondary metabolites.[2]

Melanohalea elegantula

Most Melanohalea occur primarily on bark and wood throughout the Holarctic; only four species occur in the Southern Hemisphere.[4] Melanohalea peruviana is the only species in the genus that has been reported from tropical South America, although it is poorly known – a single collection from an altitude of 4,400 feet (1,300 m) in the Peruvian Andes.[5] The only other Melanohalea species found in a tropical habitat is M. mexicana, a highland species from south central Mexico.[6] The five Melanohalea species found in Greenland may play a role in monitoring the impact of climate change, as arctic-alpine lichens are sensitive to fluctuations in the temperature of winter climates, and winter icing events affect lichen-dominated ecosystems.[7]

Most Melanohalea species have a broad geographic distribution, although there are a few that have more restricted ranges. Otte and colleagues suggested in a 2005 study that distribution patterns in Melanohalea are largely determined by contemporary ecogeographical factors, and most species have reached their biogeographical limits in the Northern Hemisphere.[8] The distributions of M. elegantula and M. exasperatula seem to be affected by anthropogenic factors, including eutrophication and air pollution.[4]

Melanohalea originally included 19 species transferred from Melanelia. In the following years, new species in the genus were described from India, Tibet, Mexico, and Peru. In 2016, Leavitt and colleagues used genetic analyses to help identify 6 previously undescribed morphologically cryptic species in Melanohalea.[9] As of June 2020, Species Fungorum accepts 30 species of Melanohalea.[10]

• Melanohalea austroamericana Essl., Divakar, A.Crespo, S.D.Leav. & Lumbsch (2016)[9]
• Melanohalea beringiana S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016)[9]
• Melanohalea clairi S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016)[9]
• Melanohalea columbiana S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016)[9]
• Melanohalea davidii S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016)[9]
• Melanohalea elegantula (Zahlbr.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea exasperata (De Not.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)

Melanohalea exasperata

• Melanohalea exasperatula (Nyl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea gomukhensis (Divakar, Upreti & Elix) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea halei (Ahti) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea inactiva (P.M.Jørg.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea infumata (Nyl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea laciniatula (Flagey ex H.Olivier) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea lobulata F.G.Meng & H.Y.Wang (2009)[11] – Tibet
• Melanohalea mexicana Essl. & R.-E.Pérez (2010)[6] – Mexico
• Melanohalea multispora (A.Schneid.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea nilgirica Divakar & Upreti (2005)[12] – India
• Melanohalea olivacea (L.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea olivaceoides (Krog) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea peruviana Essl. (2012)[5] – Peru
• Melanohalea poeltii (Essl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea septentrionalis (Lynge) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea subelegantula (Essl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea subexasperata F.G.Meng & H.Y.Wang (2010)[13] – Tibet
• Melanohalea subolivacea (Nyl. ex Hasse) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea subverruculifera (J.C.Wei & Y.M.Jiang) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea tahltan S.D.Leav., Essl., Divakar, A.Crespo & Lumbsch (2016)[9]
• Melanohalea trabeculata (Ahti) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea ushuaiensis (Zahlbr.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)
• Melanohalea zopheroa (Essl.) O.Blanco, A.Crespo, Divakar, Essl., D.Hawksw. & Lumbsch (2004)