Melanohalea species predominantly inhabit bark and wood in the Holarctic, with only a few extending into the Southern Hemisphere and rare occurrences on rocks. Notably, Melanohalea peruviana in the Peruvian Andes and M. mexicana in Mexico represent the genus's limited tropical distribution. The distribution of these lichens, which are sensitive indicators of climate and pollution effects, is largely determined by current ecological and geographical factors. Certain species show vulnerability to climate change and environmental pollutants. Many species of lichenicolous (lichen-dwelling) fungi are known to parasitise the lichen. Several Melanohalea species are listed as endangeredorcritically endangered on national red lists across Europe, reflecting their varying levels of threat due to habitat loss, pollution, and climate change. Only M. halei has been assessed globally by the IUCN and is listed as being of least concern due to its widespread distribution and stable population.
Melanohalea originally comprised 19 species, with M. exasperata serving as the type species. The species transferred to Melanohalea were formerly included in sectionVainioellae of genus Melanelia. This section, in turn, was derived from ParmeliasubgenusEuparmelia sect. Vainioellae, originally proposed by Vilmos Gyelnik in 1932. Section Vainioellae included "brown parmelioids" with wide, rounded to elongated lobes that were predominantly flat.[1] The "brown parmelioids" refers to Parmelia species lacking atranorinorusnic acid in the cortex, with a dark to medium-brown thallus colour.[4] 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.[7]
The genus name combines Melanelia with the name of the lichenologist Mason Hale, who, according to the authors, "provided the foundations for subsequent contributions to our knowledge of this family".[4]
Melanohalea lichens have a foliose (leafy) thallus that is loosely to moderately attached to its substrate. The upper size limit of the thallus is about 14 cm (5.5 in) in diameter.[9] 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 usually features pseudocyphellae on warts or on the tips of isidia; the presence of soredia and isidia is variable. The upper cortexisparaplectenchymatous (a cell arrangement where the hyphae are oriented in all directions), and measures 10–16 mm thick. The epicortex does not have pores, unlike in the related genus Melanelixia. The medulla is white, and the lower thallus surface is smooth and flat and coloured pale brown to black. Rhizines are simple (i.e., unbranched),[4] and the same colour as the lower surface.[9]
The ascomata (fruiting bodies) are apothecial, laminal, and 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. AscosporesofMelanohalea 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 (i.e., lacking partitions called septa), colourless, and measure 5–8.5 μm long by 1 μm wide.[4] The photobiont of the lichen is trebouxioid, i.e., resembling or belonging to the green algal genus Trebouxia.[9]
Melanohalea can be mistaken for certain brown species of Xanthoparmelia, which were previously categorised as Neofuscelia. They can be differentiated by their distinct reactions to nitric acid; brown Xanthoparmelia species typically have a blue-green reaction, whereas Melanohalea shows no reaction. Moreover, the cell wall composition of Melanohalea differs, consisting of isolichenan instead of the Xanthoparmelia-type polysaccharide (lichenan). Pleurosticta, although similar to Melanohalea, is characterised by wider lobes, a network of epicortical pores, and a pigment that turns violet upon reacting with both potassium hydroxide (K) and nitric acid (N). Melanelixia is identified by its pored epicortex and absence of pseudocyphellae, while Melanelia is distinguished by its flat and spread-out pseudocyphellae, as opposed to the raised pseudocyphellae found in Melanohalea.[11]
Most Melanohalea occur primarily on bark and on wood throughout the Holarctic; only four species occur in the Southern Hemisphere.[8] Occasionally, they are found growing on rock.[9]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.[12] The only other Melanohalea species found in a tropical habitat is M. mexicana, a highland species from south central Mexico,[13] and one of three Melanohalea species known to occur in that country.[14] Eight members of the genus are found in China;[15] five in Great Britain and Ireland, and seven occur in the Nordic lichen flora.[16] 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.[17] Similarly, a study of the effect of air pollution surrounding the Mongolian capital Ulan Bator showed widespread damage to a variety of lichens (where the thallus was bleached, deformed, or reduced in size), including Melanohalea septentrionalis.[18]
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.[19] The distributions of M. elegantula and M. exasperatula seem to be affected by anthropogenic factors, including eutrophication and air pollution.[8]Melanohalea olivacea and M. septentrionalis, both cold-tolerant circumpolar species, have the south-west limit of their distribution range in Switzerland. They are considered relicts of the last ice age and are vulnerable to global climate warming in that country.[20]
Melanohalea septentrionalis is listed as endangered on the Red List of Switzerland.[25]Melanohalea exasperata is on the German national Red List,[26] and is in the critically endangered category in Poland's Red list of extinct and vulnerable lichens of Poland.[27] Although M. olivacea was left off this list over uncertainties about its taxonomic status, it has been preliminarily assessed as critically endangered in Switzerland using the IUCN Red List criteria. It has received the same assessment in the neighbouring countries Germany and France.[20]M. elegantula is red-listed in Sweden.[16]Melanohalea halei is the only species in this genus that has been assessed for the global IUCN Red List. Because of its broad geographic distribution, breadth of ecological niches, and large, stable population size, it has been assessed as a least-concern species.[28]
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 speciesinMelanohalea.[29] As of January 2024[update], Species Fungorum accepts 30 species of Melanohalea.[30]
^Thell, A. (1995). "A new position of the Cetraria commixta group in Melanelia (Ascomycotina, Parmeliaceae)". Nova Hedwigia. 60 (3–4): 407–422.
^ abcdefghiBlanco, Oscar; Crespo, Ana; Divakar, Pradeep K.; Esslinger, Theodore L.; Hawksworth, David L.; Lumbsch, H. Thorsten (2004). "Melanelixia and Melanohalea, two new genera segregated from Melanelia (Parmeliaceae) based on molecular and morphological data". Mycological Research. 108 (8): 873–884. doi:10.1017/S0953756204000723. PMID15449592.
^Thell, Arne; Feuerer, Tassilo; Kärnefelt, Ingvar; Myllys, Leena; Stenroos, Soili (2004). "Monophyletic groups within the Parmeliaceae identified by ITS rDNA, β-tubulin and GAPDH sequences". Mycological Progress. 3 (4): 297–314. doi:10.1007/s11557-006-0100-1.
^Blanco, Oscar; Crespo, Ana; Ree, Richard H.; Lumbsch, H. Thorsten (2006). "Major clades of parmelioid lichens (Parmeliaceae, Ascomycota) and the evolution of their morphological and chemical diversity". Molecular Phylogenetics and Evolution. 39 (1): 52–69. doi:10.1016/j.ympev.2005.12.015. PMID16481204.
^Crespo, Ana; Kauff, Frank; Divakar, Pradeep K.; del Prado, Ruth; Pérez-Ortega, Sergio; de Paz, Guillermo Amo; et al. (2010). "Phylogenetic generic classification of parmelioid lichens (Parmeliaceae, Ascomycota) based on molecular, morphological and chemical evidence". Taxon. 59 (6): 1735–1753. doi:10.1002/tax.596008.
^ abcdefMcMullin, R. Troy (2023). Lichens. The Macrolichens of Ontario and the Great Lakes Region of the United States. Firefly Books. p. 286. ISBN978-0-228-10369-1.
^ abEsslinger, Theodore L.; Pérez Pérez, Rosa Emilia (2010). "The lichen genus Melanohalea in Mexico, including a new endemic species". Bibliotheca Lichenologica. 105: 239–245.
^Esslinger, Theodore L.; Pérez-Pérez, Rosa Emilia (2016). "Melanohalea in Mexico". In Herrera-Campos, Maria; Pérez-Pérez, Rosa Emilia; Nash III, Thomas H. (eds.). Lichens of Mexico. The Parmeliaceae – Keys, distribution and specimen descriptions. Stuttgart: J. Cramer. pp. 271–272. ISBN978-3-443-58089-6.
^ abWestberg, W.; Thell, A. (2011). "Melanohalea". In Thell, Arne; Moberg, Roland (eds.). Nordic Lichen Flora. Vol. 4. Svenska Botaniska Föreningen. pp. 76–81. ISBN978-91-85221-24-0.
^Leavitt, Steven D.; Esslinger, Theodore L.; Hansen, Eric Steen; Divakar, Pradeep K.; Crespo, Ana; Loomis, Bradley F.; Lumbsch, H. Thorsten (2013). "DNA barcoding of brown Parmeliae (Parmeliaceae) species: a molecular approach for accurate specimen identification, emphasizing species in Greenland". Organisms Diversity & Evolution. 14 (1): 11–20. doi:10.1007/s13127-013-0147-1.
^Hauck, Markus (2008). "Epiphytic lichens indicate recent increase in air pollution in the Mongolian capital Ulan Bator". The Lichenologist. 40 (2): 165–168. doi:10.1017/S0024282908007561.
^Diederich, Paul; Millanes, Ana M.; Etayo, Javier; van den Boom, Pieter P.G.; Wedin, Mats (2022). "Finding the needle in the haystack: a revision of Crittendenia, a surprisingly diverse lichenicolous genus of Agaricostilbomycetes, Pucciniomycotina". The Bryologist. 125 (2): 248–293. doi:10.1639/0007-2745-125.2.248.
^Allen, J.; Yahr, R.; Lymbery, C.; Batallas-Molina, R.; Dal Forno, M.; Howe, N.; Lendemer, J.; McMullin, T.; Mertens, A.; Paquette, H.; Petix, M.; Reese Næsborg, R.; Roberts, F.; Sharrett, S.; Villella, J. (10 May 2021). "Melanohalea halei". IUCN Red List of Threatened Species. 10 May 2021. Retrieved 5 September 2021.