Assessment Notes

Justification

This is a European endemic resembling a small blackish oyster mushroom almost always found fruiting at the base of dead Ammophila in coastal sand dunes with main subpopulations located around the Atlantic and North Sea coastlines. The name Hohenbuehelia culmicola has, until recently, also been (mis)applied to the similarly Ammophila-associated H. bonii, which usually has larger, browner and more spathulate fruitbodies. H. bonii has now been segregated as a distinct and apparently rarer species, although there might still be a few historical collections or records with associated photographs currently filed as H. culmicola which require redetermination. The relatively inconspicuous mushrooms of H. culmicola s. str. are likely to have been overlooked due to the restricted microhabitat and late/early reproductive season. There are nine countries with records since 1980 and ca. 60 sites are known including 25 from the Netherlands where suitable habitat has been relatively intensively surveyed. Using a population size estimate of 4,250 mature individuals in total, with the largest subpopulation containing 750 mature individuals, and accepting a continuing decline due to continued trampling of dunes and their conversion to other uses (golf courses, caravan sites, more permanent housing) produces an assessment of Vulnerable under criterion C2a(i).

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Taxonomic notes

Historically, Hohenbuehelia culmicola has been confused with another species now recognised as Hohenbuehelia bonii (Ainsworth et al. 2016). The occurrence of this latter species is now recognised in France, UK and the Netherlands (this last country added on basis of Flickr report of a redetermination of a “culmicola” collection). When all existing collections labelled as H. culmicola are checked, further redeterminations as H. bonii may be possible.

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Geographic range

This species is mainly restricted to coastal Ammophila stands particularly around Atlantic and North Sea coasts (with one outpost locality in inland dunes in Hungary: Babos (2004), Fraiture and Otto (2015) and A. Fraiture (in litt.). With ca. 60 fruiting sites known to have been recorded (equivalent to an area of occupancy [AOO] of ca.180km²) it could be thought to have a very restricted range. However, this species is generally not found unless as a result of deliberate and comprehensive sand dune surveys, with it forming relatively inconspicuous mushrooms. Therefore, it is likely to have been overlooked and we cannot accurately estimate the true AOO.

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Population and Trends

Dahlberg and Croneborg (2003) documented six countries with records since 1980 and Spain and Hungary (one collection each) can now be added to this list (Fraiture and Otto 2015 and A. Fraiture in litt.). It has also been reported from the Italian Adriatic coast (Pacioni 1986, Fraiture and Otto 2015). If pre-1980 records are included, then the range also includes the Republic of Ireland (Dahlberg and Croneborg 2003), however it is now thought to be extinct there. Data on fruiting abundance is lacking (numbers of occupied Ammophila plants or ramets), however there are ca. 60 fruiting sites recorded.

Although there is some evidence of declines at some occupied localities, mainly due to changing land usage on coastal dunes and tourist pressures, evidence of a quantified decline is lacking, thus ruling out the use of Criterion A. This species is generally not found unless as a result of deliberate and comprehensive sand dune surveys. It forms relatively inconspicuous mushrooms that are likely to have been overlooked due to small size, dark colour, restricted microhabitat and an often late/early reproductive season. Such dedicated survey work has been carried out in the Netherlands (E.J.M. Arnolds pers. comm.) and UK (Lost and Found Fungi Project 2019: 4yrs' search yielded no records). Therefore, there are considerable doubts remaining concerning its true distribution (whether it qualifies for "severely fragmented"). Some historic records could be of the recently described species Hohenbuehelia bonii which can co-occur with H. culmicola s. str.

To calculate the population size it is estimated that there are two genets inside each occupied Ammophila clump and two ramets per genet. Surveyed sites in the UK had only one to few occupied Ammophila clumps, so it is estimated that there would be on average five occupied clumps per site. Applying a scaling factor of five to estimate the true number of sites (and this seems a high estimate) and excluding the more intensively surveyed Dutch sites, we obtain 100 x 35 (known sites outside of the Netherlands) which gives 3,500 mature individuals in total. Due to greater survey intensity in the Netherlands, a factor of 1.5 rather than five seems more appropriate to account for the as yet unknown Dutch population. This gives a Dutch total of 750 mature individuals, which represents the largest individual subpopulation, and a grand total of 4,250 mature individuals.

Population Trend: Decreasing

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Habitat and Ecology

This species is found in coastal sand dunes, rarely inland dunes, growing saprotrophically on Ammophila (also rarely on other Poaceae in the same habitat such as Leymus arenarius). It has narrow niche requirements, i.e. dynamic sand dune ecosystems with sparse vegetation of herbs and grasses.

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Threats

Threats to this species are mainly from the conversion of coastal dunes to conifer plantations, caravan/camping sites, golf courses or other developments and, on a slower timescale, to visitor pressure and recreational disturbance (trampling, vehicles). Some UK sites have diminishing Ammophila stands due to spread of Hippophae rhamnoides and management of this shrub can cause further damage to Hohenbuehelia culmicola's habitat. Storm surges and long-term sea level rise, coupled with the associated coastal management responses, present a clear threat to dynamic dune systems upon which this species depends. Inland dune systems are under even higher threats of overgrowth, tree plantations and other changes of land use causing changes in edaphic and vegetation composition.

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Conservation Actions

It is considered Red Listed in around half of the countries of occurrence. Further research is needed to inform practical conservation action. The main focus of research should be on further systematic surveys of suitable habitat and checking of historic collections labelled "H. culmicola" to determine whether redetermination as H. bonii is required. Surveillance is also important to reveal how its fruiting presence (size and location of occupied grass culms/roots) changes from year to year to assess how ruderal this species is. Population genetics studies are required to estimate the number of genets per plant and to locate the whereabouts of the fungus within the plant (root systems or separate stems). Further ecological research is also required to determine whether particular Ammophila-dominated habitats are favoured or whether the age/vigour of the plants can provide clues to help direct field survey work to areas of dune which might yield further records of reproductive individuals of H. culmicola.

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Use and Trade

No use is currently known as the mushrooms are too small to be assessed for their edibility by wild food foragers.

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Source and Citation

Ainsworth, A.M. 2024. Hohenbuehelia culmicola. The IUCN Red List of Threatened Species 2024: e.T70414794A247852484. Accessed on 22 November 2025.

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• Country occurrence