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Chlorostroma vestlandicum B. Nordén & Læssøe

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Scientific name
Chlorostroma vestlandicum
B. Nordén & Læssøe
Common names
IUCN Specialist Group
Cup-fungi, Truffles and Allies
Assessment status
Preliminary Category
EN C2a(i)
Proposed by
Thomas Læssøe
Thomas Læssøe, Björn Nordén
Tommy Knutsson
Comments etc.
Anders Dahlberg, John Bjarne Jordal, Michael Krikorev

Assessment Notes


Chlorostroma vestlandicum is a fairly conspicuous and characteristic stromatic pyrenomycete only known from western Norway. It is a highly distinctive species due to a strikingly orange entostroma, tiny perithecia and specialized association to the wood-decay fungus Hypoxylon. vogesiacum. It is a highly specialized species that parasitizes the rare H. vogesiacum, confined to coarse dead wood of Ulmus glabra (wych elm), in particular huge decaying trunks of earlier pollarded veteran trees. Hypxylon vogesiacum and U. glabra are nationally red-listed in Norway and Sweden. Within Europe, the populations of U. glabra are declining due to Dutch Elm Disease (DED), but is globally assessed as Data Deficient due to distribution extending into western Asia and Russia (2017).

Chlorostroma vestlandicum was discovered in 2010 and described from western Norway in 2014. It is after investigations of hundreds of alms in 50 locations throughout southern Norway in the 2011-2014 known from 12 sites. The total number of sites is not considered to exceed 200 and the number of fungal individuals not to exceed 10/site.

Because of DED and deer feeding on bark of live older trees U.glabra, and hence the habitat of C. vestlandicum, is declining in Norway. DED is not known in today’s range, but is a significant future threat of C. vestlandicum. Presently, the impact of deer is a serious threat for the elm population in Western Norway. Chlorostroma westlandicum is red-listed as EN by C2a (i) based on an estimated total populatioon not to exceed 2500 individuals, ongoing reduction in habitat and population and small sub-populations.

Taxonomic notes

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

Why suggested for a Global Red List Assessment?

This is a fairly conspicuous and characteristic stromatic pyrenomycete. Recently described but so far World distribution is confined to western Norway. The species is highly specialized and parasitizes the rare and redlisted Hypoxylon vogesiacum a species that in turn only occurs on huge decaying trunks of earlier pollarded veteran trees of the redlisted Ulmus glabra.

Chlorostroma vestlandicum was described from coarse dead wood of Ulmus glabra in western Norway in 2014. 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 ahighly distinctive species. C. vestlandicum differs from the type species by the color of the entostroma (bright yellow orange as opposed to ochraceous), iodine reaction of the apical apparatus, ascospores (more or less ellipsoid as opposed to more or less cuboid). The surface is not green or bluegreen as in previously described species, albeit dark greenish blackish in section.

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.

Using templates (Dahlberg & Mueller 2011) the three generation time is estimated to 50 years.
So far only known from 10 localities in Norway. Including a relatively large darkness figure of x50 a rough estimate of less than 500 localities are expected on a global scale. Using template for wood inhabiting fungi (Dahlberg & Mueller 2011) this gives an estimate of less than 5000 mature individuals.

Criteria: VU C2a(i)

Geographic range

Confined to western Norway

Population and Trends

So far Chlorostroma vestlandicum is only known from c. 10 localities in Norway. Inclusion of a relatively large darkness figure of x50 gives a rough estimate of less than 500 localities are expected on a global scale. Using template for wood inhabiting fungi (Dahlberg & Mueller 2011) this gives an estimate of less than 5000 mature individuals.
Habitat is under serious threats from change of land use practices and Dutch elm disease in close future.

Population Trend: Decreasing

Habitat and Ecology

There is little doubt that Clorostroma vestlandicums is closely associated with Hypoxylon vogesiacum and its distribution is probably partly delimited by the distribution of its fungal host. The species is found on wood of Ulmus glabra; on coarse logs of old trees or on coarse fallen branches, or on dead parts of still living trees, always associated with stromata of H. vogesiacum. All findings were made in deciduous forests dominated by U. glabra (and sometimes Fraxinus excelsior), at a height of up to 250 meters above sea level. The species (like its host) seems to prefer relatively warm summers, but shows no clear affinity to oceanic or continental climate.H. vogesiacum was described from France and is furthermore known from Sweden, Finland, Austria, Switzerland, and Spain as well as from North America and Asia. H. vogesiacum has a hemiboreal distribution in the Nordic countries (Granmo et al. 1989), and has not been found in for example Denmark or in the UK. In Norway H. vogesiacum is widely distributed in the warmest parts of southern Norway north to Trøndelag, with its largest populations in western Norway. It mainly grows on Ulmus and occasionally on Fraxinus in parts of Europe including Sweden and Norway.

Temperate Forest


Main threats is the small population size and AAO 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.
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. 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 (both as NT; Kålås et al. 2010) and declining, and C. vestlandicum therefore warrant attention in conservation work.

Shifting agricultureNamed species

Conservation Actions

All known sites in need of area-specific protection and managment plans. All known localities is very rich in other rare and red-listed species. Monitoring the spread of Dutch Elm disease is important in order to try and stop the spreading when entering the core area of distribution of Chlorostroma vestlandicum.

Site/area protectionSite/area managementInvasive/problematic species controlHabitat & natural process restorationConservation payments

Research needed

Population size, distribution & trendsHabitat trends

Use and Trade


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.

Known distribution - countries

Regional Population and Trends

Country Trend Redlisted