Melanohalea Exasperata

''Melanohalea'' is a genus of foliose lichens in the family Parmeliaceae. It contains 30 mostly Northern Hemisphere species that grow on bark or on wood. The genus is characterized by the presence of pseudocyphellae, usually on warts or on the tips of isidia, a non-pored and a medulla containing depsidones or lacking secondary compounds. ''Melanohalea'' was circumscribed in 2004 as a segregate of the morphologically similar genus ''Melanelia''.

Taxonomy

''Melanohalea'' was circumscribed in 2004 by lichenologists Oscar Blanco, Ana Crespo, Pradeep K. Divakar, Theodore Esslinger, David L. Hawksworth and H. Thorsten Lumbsch. It is a segregate of ''Melanelia'', a genus created in 1978 to contain the brown '' Parmelia'' species. The circumscription of this genus was questioned later, especially after early molecular phylogenetics studies demonstrated that it was not monophyletic. Subsequently, two genera, ''Melanelixia'' and ''Melanohalea'', were created.

''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. The "brown parmelioids" refers to ''Parmelia'' species lacking atranorin or usnic acid in the cortex, but having a dark to medium-brown thallus colour. 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''.

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".

Diversification

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''.

Description

''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 usually features pseudocyphellae on warts or on the tips of isidia; the presence of soredia and isidia is variable. The upper cortex is (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).

The ascomata are apothecial, , sessile to more or less pedicellate. The apothecial is brown, and is not perforated. It is initially concave but becomes convex with age. The (a layer of cells that surrounds the apothecium) has pseudocyphellate , 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 (i.e., lacking partitions called septa), colourless, and measure 5–8.5 by 1 μm long.

Chemistry

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. ''M. nilgirica'' contains the aliphatic compound caperatic acid, which is rare in the brown parmelioid lichens, known only to exist in ''Melanelia stygia'', the type species of ''Melanelia''.

Habitat and distribution

Most ''Melanohalea'' occur primarily on bark and wood throughout the Holarctic; only four species occur in the Southern Hemisphere. '' 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 in the Peruvian Andes. The only other ''Melanohalea'' species found in a tropical habitat is '' M. mexicana'', a highland species from south central Mexico. Eight members of the genus are found in China; seven occur in the Nordic lichen flora. 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. 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''.

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. The distributions of ''M. elegantula'' and ''M. exasperatula'' seem to be affected by anthropogenic factors, including eutrophication and air pollution. ''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 global climate warming in that country.

Ecology

Several species of lichenicolous fungi have been recorded growing on ''Melanohalea'' species. These include '' Epithamnolia xanthoriae'', '' Xenonectriella septemseptata'', ''Plectocarpon melanohaleae'' (on ''M. ushuaiensis''), ''Abrothallus bertianus'', ''Zwackhiomyces melanohaleae'' (on ''M. exasperata''), '' Phoma melanohaleicola'' (on ''M. exasperata''), ''Didymocyrtis consimilis'', ''Stigmidium exasperatum'' (on ''M. exasperata''), ''Sphaeropezia melaneliae'' (on ''M. olivacea''), ''Arthrorhaphis olivaceae'' (on ''M. olivacea''), '' Epithamnolia xanthoriae'', '' Xenonectriella septemseptata'', ''Plectocarpon melanohaleae'' (on ''M. ushuaiensis''), ''Crittendenia coppinsii'' (on ''M. exasperatula''), and '' Stagonospora exasperatulae'' (on ''M. exasperatula'').

Conservation

''Melanohalea septentrionalis'' is listed as endangered in the Red List of Switzerland. 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. ''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.

Species

''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''. , Species Fungorum accepts 30 species of ''Melanohalea''.
*'' Melanohalea austroamericana''
*'' Melanohalea beringiana''
*''Melanohalea clairi''
*'' Melanohalea columbiana''
*'' Melanohalea davidii''
*'' Melanohalea elegantula''
*''Melanohalea exasperata''

*'' Melanohalea exasperatula''
*''Melanohalea gomukhensis''
*'' Melanohalea halei''
*'' Melanohalea inactiva''
*'' Melanohalea infumata''
*'' Melanohalea laciniatula''
*'' Melanohalea lobulata'' – Tibet
*'' Melanohalea mexicana'' – Mexico
*''Melanohalea multispora''
*''Melanohalea nilgirica'' – India
*'' Melanohalea olivacea''
*'' Melanohalea olivaceoides''
*'' Melanohalea peruviana'' – Peru
*'' Melanohalea poeltii'' – Nepal; India
*'' Melanohalea septentrionalis'' – North America; Europe; Asia
*'' Melanohalea subelegantula'' – western North America; Tibet
*'' Melanohalea subexasperata'' – Tibet
*''Melanohalea subolivacea''
*''Melanohalea subverruculifera''
*''Melanohalea tahltan''
*'' Melanohalea trabeculata''
*'' Melanohalea ushuaiensis''
*'' Melanohalea zopheroa''

References

{{Taxonbar, from=Q10580432

Lecanorales genera
Lichen genera
*
Taxa described in 2004
Taxa named by Ana Crespo
Taxa named by Helge Thorsten Lumbsch
Taxa named by David Leslie Hawksworth
Taxa named by Pradeep Kumar Divakar