Ionomidotis irregularis is a rare European temperate - boreal saprotrophic ascomycete that inhabits trunks of a deciduous trees species eg. Alnus incana, Betula spp., Populus spp., Carpinus betulus and Fagus sylvatica. The species grows in old-growth forests, virgin forests and forests with natural forest succession. It is a rare species restricted to localities with humid microclimate with wet dead wood and with immediate presence of a brook or ravine. The species is a indicator species of old, unmanaged mixt forests rich in broadleaved trees that develop into spure dominated in boreal vegetation zone (von Bonsdorff et al. 2014). Known localities are very fragmented.

The species is easily identified by it´s quite large and irregular cup-like densly punctate ascocarps on dead wood.The species is declining due to forest management. It is nationally red-listed in Estonia as Vulnerable (VU) and in Finland as Endangered (EN).

Ionomidotis irregularis is known from about 50 sites in Europe. The estimated total number of sites is around 500 corresponding to about 5000 individuals. Its habitat of old and virgin forests of is presently facing and expected to continue to have a more than 30% decline in quality and quantity, due to forestry and deforestation (eg. Janssen et al. 2016, Kouki et al. 2018). The decline of the major habitat of the species, old-growth forest and virgin forests, in the evaluation period (30 years; Dahlberg and Mueller 2011) it is estimated to be more than. The decline of the species is estimated to be the same magnitude as the impact of its habitat. For these reasons I. irregularis is assessed to meet the category Vulnerable (VU ) under the A-criteria (A2c+3c+4c) and the C-criteria C2a(i).

Ionomidotis irregularis was decribed 1923 in USA. ITS-sequences suggests the European and North American taxon are different but closely related (Irja Saar pers. comm. with informatin from Unite). This assessment only consider the European taxon.

Note to James: Ionomidotis irregularis is described in USA 1832 on leaves (?) (or 1923 according to Genbank) . I am not sure how to handle the name here. See below

http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=231953

Ionomidotis irregularis is recorded from 11 European countries: Austria, Czechia, Estonia, Finland, Hungary, Norway, Poland, Russia, Slovakia, Spain and Switzerland.

The species is rare in Europe, known from a few localities only in each 11 recorded country, in total approximately 50 localities (Estonia (22), Czechia (3), Slovakia (4), Switzerland (1), Norway (2), Finland (2), Austria (4), Hungary (1), Spain (3) and Russian Federation (approx.10)). As the sporoarps of I. irregularis are conspicous and the species´habitat requirment specific and quite well-known, the total number of localities is estimated to be approx. 500 localities. Assuming two occurences per site and 10 individuals per occurence, this corresponds to a total population of approx. 5 000 individuals (Dahlberg & Mueller, 2011).

The past and ongoing decline of the key habitats of the species, old-growth and virgin forests it is estimated to be in the magnitude of >30% in a 30-year perspective (Kouki et al. 2018. ADD EUROPEAN ASSESSMENT). The decline of the species is estimated to be the same magnitude (cf. Dahlberg and Mueller 2011).

Based on this, the species is assessed as VU according to the A-criterion (A2c + 3c + 4c) (past and ongoing species/habitat decline >30 %) and ongoing decline together with the estimated population size of 5000 individuals also the C-criterion (C2a(i).

Ionomidotis irregularis is a temperate - boreal saprotrofic ascomycete producing sporcarps on strongly decayed mossy trunks of a deciduous trees species eg. Alnus spp. Betula spp., Ulmus glabra, Populus spp., Carpinus betulus and Fagus sylvatica. The species grows in old-growth forests, virgin forests and forests with natural forest succession. in the immediate presence of a brook, brook-side habitats (Běťák et al. 2012, von Bonsdorff et al. 2014).

The population of Ionomidotis irregularis has declining and is continuing to decline as a consequence of (1) declining habitat (old-growth forests/virgin forests, riparian hardwood forests) and decreasing habitat qulity (eg. decrasing amount of dead wood) due to intensive forestry. In Finland, these forests are redlisted as EN (mesic - herb-rich coniferous forests) and old mixt forests dominated with decidous trees as VU (Kouki et al. 2018). At the European level, the EU Red List classify appropriate temperate and boreal hardwood riparian woodland habitats as EN and other suitable habitats as VU (Janssen et al. 2016).

Anders: Add some general for the overall distribution

Protection of the old forests with decidous trees, leaving dead wood to the forests. Logging/harvesting and water drainadge forbidden nearby these brooksides/ravins.

Taxonomical research needed in Ionomidotis irregularis group (eg. Asia & North America).

No uses have been recorded.

Běťák J., Pärtel K. & Kříž M. 2012: Ionomidotis irregularis (Ascomycota, Helotiales)
v České republice s poznámkami k jeho rozšíření a ekologii v Evropě. – Czech
Mycol. 64(1): 79–92.

Dahlberg, A. and Mueller, G. 2011: Applying IUCN red-listing criteria for assessing and reporting on the
conservation status of fungal species. Fungal Ecology 4: 1-16.

von Bonsdorff T., Kytövuori I., Vauras J., Huhtinen S., Halme P., Rämä T., Kosonen L. & Jakobsson S. 2014: Sienet ja metsien luontoarvot. — Norrlinia 27: 1–272. (Fungi of the forests with high conservation value in Finland – indicator species).

Huhtinen, S., Söderholm, U., von Bonsdorff, Purhonen, J., Kosonen, T., Kekki, T., Halme, P., Ohneoja, E., Ruotsalainen, A.-L. & Salo, P.  2019: Ascomycetes. In: Hyvärinen, E., Juslén, A., Kemppainen, E., Uddström, A. & Liukko, U.-M. (eds.) 2019. The 2019
Red List of Finnish Species. Ympäristöministeriö & Suomen ympäristökeskus. Helsinki. pp. 204-233.

Janssen, J.A.M., Rodwell, J.S., García Criado, M., Gubbay, S., Haynes, T., Nieto, A., Sanders, N., Landucci, F., Loidi, J., Ssymank, A., Tahvanainen, T., Valderrabano, M., Acosta, A., Aronsson, M., Arts, G., Attorre, F., Bergmeier, E., Bijlsma, R.-J., Bioret, F., Biţă-Nicolae, C., Biurrun, I., Calix, M., Capelo, J., Čarni, A. Poulos, P., Essl, F., Gardf, Chytrý, M., Dengler, J., Dimojell, H., Gigante, D., Giusso del Galdo, G., Hájek, M., Jansen, F., Jansen, J., Kapfer, J., Mickolajczak, A., Molina, J.A., Molnár, Z., Paternoster, D., Piernik, A., Poulin, B., Renaux, B., Schaminée, J.H.J., Šumberová, K., Toivonen, H., Tonteri, T., Tsiripidis, I., Tzonev, R. and Valachovič, M. 2016. European Red List of Habitats. Part 2. Terrestrial and freshwater habitats. European Union, Luxembourg.

Kouki J., Junninen K., Mäkelä K., Hokkanen M., Aakala T., Hallikainen V. et al. 2018: Forests 6. In: Kontula T., Raunio A. (eds.): Threatened habitat types in Finland 2018, Red List of habitats. Part II: Descriptions of habitat types. - Helsinki: Suomen ympäristökeskus. 2018. p. 475-567. (Suomen Ympäristö).