European endemic resembling a small blackish oyster mushroom almost always found fruiting at the base of dead Ammophila in coastal sand dunes with main populations located around the Atlantic and North Sea coastlines. The name H. 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.
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. Applying Criterion C, using an estimate of <10,000 mature individuals in total, but fewer than 1000 mature individuals in each subpopulation, and accepting a continuing decline in habitat quality from continued trampling of dunes and their conversion to other uses (golf courses, caravan sites, more permanent housing) produces an assessment of VU C2a(i)

Assumptions and data: 2 genets inside each occupied Ammophila clump and 2 ramets per genet. Surveyed sites in the UK had only one to few occupied Ammophila clumps so if we estimate 5 occupied clumps per site and apply x5 to estimate the true number of sites (and this seems a high estimate) and exclude the more intensively surveyed Dutch sites, we obtain 100 x 35 (known sites) which gives 3500 mature individuals in total. Due to greater survey intensity in the Netherlands, a factor of x1.5 rather than x5 seems more appropriate to account for the as yet unknown Dutch population. This gives a Dutch total of 750 mature individuals and a grand total of 4250 mature individuals. The largest subpopulation along the Dutch coastline is estimated to comprise ca. 750 mature individuals.

Two marram oyster species (Ainsworth et al. 2016) are now accepted as extant in France, the UK and the Netherlands. When all available collections and records with associated photographs are checked, this could further diminish the number of historic records of H. culmicola s.str.

Anders to Martyn (now addressed): Qualify for EN or VU, no of known mature individuals (45 locations corresponds to 450 mature individuals if max 1 genotype/site). Hoe many times more locations do you estimate is present? Now the estimate is not more than x 5 (if two or more genotypes/site, fewer sites).
Martyn to Anders: I don’t think there will be 10 ramets per genet - I think there are few (1 or 2) genets inside each Ammophila clump and a similar number of ramets per genet. The sites I’ve surveyed had only one to few occupied clumps (fruiting patches) so if we estimate 5 occupied clumps per site then even if we have x5 for estimate of true number of sites (and this seems a high estimate) we remain within VU.
Martyn14April2021: revised assessment based on latest records (and intensive recording in NL)

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 & Otto (2015) and A. Fraiture (in litt.)

Dahlberg & Croneborg (2003) documented 6 countries with records since 1980 and Spain and Hungary (1 collection) can now be added to this list (Fraiture & Otto 2015 and A. Fraiture in litt.). It has also been reported from the Italian Adriatic coast (Pacioni 1986, Fraiture & Otto 2015). If pre-1980 records are included, then the range also includes the Republic of Ireland (Dahlberg & Croneborg 2003). Data on fruiting abundance is lacking (numbers of occupied Ammophila plants or ramets), however there are ca. 60 fruiting sites recorded (equivalent to a maximum AOO of ca.180km2). Considered red-listed in around half of the countries of occurrence and now thought to be extinct in Ireland. Although there is some evidence of habitat decline 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 Criterion A. May possibly qualify for Criterion B since ca. 60 fruiting sites are known to have been recorded (equivalent to a maximum AOO of ca.180km2) but 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 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 & Found Fungi Project: 4yrs’ search yielded no records). Therefore there are considerable doubts remaining concerning its true distribution (whether it qualifies for “severely fragmented”) and its population size. Some historic records could be of the recently described species H. bonii which can co-occur with H. culmicola s.str. Criterion C seems most readily appropriate, using an estimate of <10,000 mature individuals in total, but less than 1000 mature individuals in each subpopulation, and accepting a continuing decline in habitat quality from continued trampling of dunes and their conversion to other uses (golf courses, caravan sites, more permanent housing).

Coastal sand dunes, rarely inland dunes growing saprotrophically on Ammophila (also rarely on other Poaceae in same habitat such as Leymus arenarius). Narrow niche requirements, i.e. dynamic sand dune ecosystems with sparse vegetation of herbs and grasses.

Threats are mainly from conversion of coastal dunes to conifer plantations, caravan/camping sites, golf courses or other development and, on a slower timescale, to visitor pressure and recreational disturbance (trampling, vehicles). Some UK sites have diminishing Ammophila stands due to invasion by Hippophae rhamnoides and management of this shrub can cause further damage to H. culmicola 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.

Further research needed to inform practical conservation action

The main focus of research should be on further systematic survey 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 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 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.

None currently known, mushrooms are too small to be assessed for their edibility by wild food foragers

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