European endemic resembling small oyster mushroom restricted to coastal sand dunes and fruiting at the base of dead Ammophila. Only distinguished from H. culmicola at specific rank in 2016 (but recognised as a distinct taxon since 1970) and currently only known from 3 countries (and formerly, in 1949, in the Republic of Ireland). The relatively inconspicuous mushrooms are likely to have been overlooked due to the restricted microhabitat. Although current evidence suggests this is much rarer than H. culmicola s.str., this assessment accepts that the two species were historically confused and therefore cautiously assumes the population and threats are the same as those for H. culmicola. 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). This yields an assessment of VU C2a(i)

Two marram oyster species (Ainsworth et al. 2016) now recognised as present in France, UK and the Netherlands (this last country added on basis of Flickr report of a redetermination of a “culmicola” collection). When available collections are checked, this could increase the number of historic records of H. bonii. Earlier synonyms are Acanthocystis petaloides var. macrospora Bon 1970 and H. petaloides var. macrospora Courtecuisse 1985.
The two taxa were synonymised in Fraiture & Otto (2015)

Restricted to coastal Ammophila stands particularly around Atlantic and North Sea coasts. Not recorded in the Republic of Ireland since 1949

6 sites known from UK (1 site known to have produced fruitbodies for two decades), but only seen on a few (<10) culms of Ammophila at each site. One record known from the Netherlands but described as a “characteristic species on the Northern French dune habitat (Guinberteau 2011). Possibly extinct in Ireland.

Coastal sand dunes, rarely inland dunes growing saprotrophically on Ammophila (possibly also on other Poaceae in same habitat such as Leymus arenarius, which was recorded at one English site). 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 caravan/camping sites, golf courses or other development and, on a slower timescale, to visitor pressure and recreational disturbance (trampling). Changes in large-scale offshore dredging activities are also suspected to alter coastal dynamics unfavourably for this species, for example by shifting the prevailing deposition from sand to pebbles and shingle accretion (Kent, UK). 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.

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.

Ainsworth, A.M., Suz, L.M. & Dentinger, B.T.M. (2016). Hohenbuehelia bonii sp. nov. and H. culmicola: two pearls in the marram oyster. Field Mycology 17(3):78-86

Bon, M. (1970). Flore héliophile des macromycètes de la zone maritime picarde. Thèse de doctorat en Pharmacie (Faculté de Lille). Bull. Soc. Myc. Fr. 86(1): 79–213.

Bon, M. (1980a) [1979]. Taxons nouveaux. Doc. Mycol. 10(37–38): 89–92.

Bon, M. (1980b). Quelques Agaricales “greffees” sur Ammophila arenaria (L.) Link. Doc. Mycol. 11(41):
47–54.

Bon, M. (1988). Flore mycologique du littoral. Doc. Mycol. 19(74): 62–64.

Buczacki, S. (2012). Collins fungi guide. HarperCollins, London.

Courtecuisse, R. (1985) [1984]. Transect mycologique dunaire sur la Côte d’Opale (France) part 1. Doc. Mycol. 15(57–58): 1–115.

Courtecuisse, R. & Duhem, B. (1995). Mushrooms & Toadstools of Britain & Europe (Collins Field Guide). HarperCollins, London

Dahlberg A & Croneborg H. 2003. 33 threatened fungi in Europe. Complementary and revised information on candidates for listing in Appendix I of the Bern Convention T-PVS (2001) 34 rev 2.

Fraiture, A. & Otto, P. (2015). Distribution, ecology and status of 51 macromycetes in Europe. Meise Botanic Garden.

Guinberteau, S. (2011).  Le petit livre des champignons des dunes. Éditions confluences, Bordeaux

LAFF (Lost and Found Fungi Project). http://fungi.myspecies.info/content/lost-found-fungi-project

Ludwig, E. (2000). Pilzkompendium Band 1 Abbildungen. IHW Verlag.

Ludwig, E. (2001). Pilzkompendium Band 1 Beschreibungen. IHW Verlag.