Chlorostroma vestlandicum was discovered in 2011 and described from western Norway (Nordén et al. 2014). After surveying a large number of sites throughout western/southern Norway in the period 2011-2020 it is currently known from 23 sites (>1km apart). Recently, it was also discovered from 3 sites in western (European) Russia (E. Popov pers. comm.). Chlorostroma vestlandicum is a fairly conspicuous and characteristic stromatic pyrenomycete, and is probably a rare species with a limited distribution. It is a highly distinctive species due to a strikingly orange entostroma, a specialized association with the wood-decay fungus Hypoxylon vogesiacum, and only found in connection with this on dead wood of Ulmus glabra (wych elm). In Norway, H. vogesiacum and U. glabra are nationally red-listed as NT and VU respectively. The substrate and supposed fungal host of C. vestlandicum will in the future be declining in its main distribution area. Dutch Elm Desease (DED) affects so far only the populations in SE Norway (one locality, Vestfold) and has not spread to western Norway, but this disease is a significant future threat to C. vestlandicum in its entire distribution area.
There is an estimate of 150 localities in Norway (estimate from Norwegian red list 2021). Outside Norway we estimate the species to be present in less than 100 localities. Using the template for wood inhabiting fungi (10 individuals/site; Dahlberg & Mueller 2011) this gives an estimate of less than 2500 mature individuals globally.
C. vestlandicum is EN in Norway and not evaluated in Russia. The known population is completely restricted to smaller parts of N. Europe. In its distribution range, it is considered to suffer from a decline in host trees and in the associated Hypoxylon vogesiacum by 15-30% during three generations in present and future (30 years) caused by fungal pathogens, red deer damage to elm trees, and competition from the invasive Acer pseudoplatanus. Ulmus glabra is therefore VU both in Norway (where the main known population of C. vestlandicum is) and in Europe as a whole (Rivers 2017). Chlorostroma vestlandicum is assessed as EN C2a (i) based on an estimated total population not exceeding 2500 individuals, ongoing reduction in habitat and population and small sub-populations (<250 individuals).

The species belongs to a genus with two further species, both being parasites of Hypoxylon species.

This is a fairly conspicuous and characteristic stromatic pyrenomycete. Recently described but so far world distribution is confined to western Norway, one place i SE Norway, and St. Peterburg surroundings of W Russia. The species is highly specialized and parasitizes the rare Hypoxylon vogesiacum, a species that in turn mainly occurs on decaying trunks or branches of veteran trees of Ulmus glabra. Chlorostroma vestlandicum was described from coarse dead wood of Ulmus glabra in western Norway (Nordén et al. 2015). It was invariably found in close association with Hypoxylon vogesiacum and appears to be mycoparasitic on this species. With a strikingly orange entostroma, tiny perithecia and specialized habitat association it is a highly distinctive species, which should have been discovered earlier if widely distributed. Its distribution seems to cover mainly the hemiboreal regions of western Norway, an area not yet affected but threatened by Dutch elm disease. It is probably a rare species restricted to localities rich in coarse dead wood and large populations of its host H. vogesiacum.

Chlorostroma vestlandicum is known from Norway and Russia. In Norway, 22 of 23 sites are lying in western Norway (including mid Norway). The last one is an isolated site in SE Norway. In addition three new records were recently found in western Russia (European part not far from St. Petersburg (E. Popov pers. comm.).Since C. vestlandicum is a prominent species it should have been described earlier if widely distributed in Europe, It most probably has a much narrower distribution than its host, possibly defined by climatic and/or historic factors.

Chlorostroma vestlandicum was first found in W Norway in 2011. The hosts of Chlorostroma vestlandicum, the fungus Hypoxylon vogesiacum growing on dead wood of the tree Ulmus glabra, are both nationally red-listed in Norway (as NT and VU respectively). Ulmus glabra is supposed to have an ongoing decline of 30-50% (or may be >50%) during 90 years. Hypoxylon vogesiacum has its largest European population in western parts of Norway, where old trees of Ulmus glabra are still common whithout being exposed to Dutch Elm Desease (DED). Hypoxylon vogesiacum is here supposed to have a decline of 15-30% in 30 years. Within Europe, the populations of U. glabra are also declining (10-40% in the past century; >30% in the coming century), and the species is assessed as VU (Rivers 2017) (globally, Ulmus glabra is DD; Barstow & Rivers 2017). In Western Russia DED is present with serious impact on urban populations, but good data on the wild populations of Ulmus glabra is lacking (E. Popov pers. comm.). Based on this, Chlorostroma is supposed to have an ongoing and future decline of 15-30% during 3 generations (30 years). Its habitat is under serious threats (see threats).

There is an estimate of 150 localities in Norway (propose to red list 2021), as the species has been much searched for the last 10 years. Outside Norway we suppose less than 100 localities. Using template for wood inhabiting fungi (10 individuals/site; Dahlberg & Mueller 2011) this gives an estimate of less than 2500 mature individuals.

Chlorostroma vestlandicum seems to be associated with Hypoxylon vogesiacum (probably parasitic) and its distribution and population size is probably partly delimited by the distribution and population size of its fungal host. C. vestlandicum is found on coarse logs of old trees or on fallen branches of Ulmus glabra, or on dead parts of still living trees. Most Norwegian and at least one of the three Russian collections were associated with stromata of H. vogesiacum (E. Popov pers. comm.). According to current knowledge, C. vestlandicum has a much narrower distribution than H. vogesiacum. All findings of C. vestlandicum in Norway were made in deciduous forests with U. glabra, up to 320 meters above sea level. The species (like its hosts) seems to prefer relatively warm summers. H. vogesiacum was described from France and is furthermore reported from Sweden, Finland, Austria, Switzerland, and Spain (and further from North America and Asia which could be other species), but C. vestlandicum has never been found in these countries. H. vogesiacum has a hemiboreal distribution in the Nordic countries (Granmo et al. 1989, Granmo 1999, Nordén et al. 2014). In Norway, C. vestlandicum is distributed in the warmest parts of southern Norway north to Trøndelag, with its largest populations in western Norway, one of the few regions in Europe where the Dutch Elm Desease is still absent on Ulmus.

The main threats are the small population size, a small and fragmented population together with decline of suitable Ulmus logs due to change in habitat management and an increase in red deer population affecting re-establishments of new decidious trees. Dutch elm disease is also an obvious threat which will kill all host if, as is predicted, it will reach the habitats of Chlorostroma vestlandicum in western Norway (hithertoe not discovered here). It should be searched for in other areas with a similar climate in Europe. Both Ulmus glabra and its apparent host species H. vogesiacum are nationally red-listed in Norway and declining, and C. vestlandicum therefore warrant attention in conservation work.

Both Ulmus glabra and H. vogesiacum are nationally red-listed and declining in Norway (as VU and NT respectively; Artsdatabanken 2015), and C. vestlandicum (EN in Norway) therefore warrant attention in conservation work. All known sites are in need of area-specific protection and management plans. The known localities are very rich in other rare and red-listed species. Monitoring the spread of Dutch Elm disease is important in order to stop the spreading when approaching the core area of distribution of Chlorostroma vestlandicum. Control of too large red deer populations and delimitation of the spreading of the invasive Acer pseudoplatanus is desirable.

We should know more about the life strategy of Chlorostroma vestlandicum and its connection to Hypoxylon vogesiacum. Since C. vestlandicum is a prominent species it should have been described earlier if widely distributed in Europe, it most probably has a much narrower distribution than its hosts Ulmus glabra and Hypoxylon vogesiacum, possibly defined by climatic, historical or ecological factors. It should be searched for in other areas with a similar climate in Europe.
Hypoxylon vogesiacum is also found on other trees like Fraxinus excelsior. C. vestlandicum is only encountered on Ulmus glabra, can it also live on other trees? The knowledge of the population dynamics of Ulmus glabra and Hypoxylon vogesiacum has many gaps which should be filled.

There is no use or trade of this species. In western Norway, its host tree Ulmus glabra was formerly used for pollarding (cutting branches for fodder), which was not a threat for C. vestlandicum. The timber of its host tree Ulmus glabra is strong, durable and water resistant, and has in Europe been used as material for different purposes (boats, furniture etc.; Rivers 2017).

Barstow, M. & Rivers, M.C. 2017. Ulmus glabra. The IUCN Red List of Threatened Species 2017: e.T61966807A61966819. http://dx.doi.org/10.2305/IUCN.UK.2017-3.RLTS.T61966807A61966819.en [global assessment]
Nordén, B., Læssøe, T. & Jordal, J.B. 2014. Chlorostroma vestlandicum sp. nov., a host-specific mycoparasite on Hypoxylon vogesiacum from western Norway. Karstenia 54: 9-13.
Rivers, M.C. 2017. Ulmus glabra. The IUCN Red List of Threatened Species 2017: e.T61966807A80570504. https://www.iucnredlist.org/species/61966807/80570504.  Downloaded on 05 March 2021. [Assessment for Europe].