R-L categories correct, but text may not match final assessment. Updated version will be published in IUCN´s Red List.
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 at varietal rank 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 and late/early reproductive season. Although current evidence suggests this is much rarer than H. culmicola s.str., this assessment acknowledges that the two species were historically confused and not recognised as distinct entities. A few historical collections or records with associated photographs currently filed as H. culmicola might therefore be redetermined as H. bonii. The habitat 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 fewer than 1000 mature individuals in each subpopulation, and accepting a continuing decline in habitat quality from continued trampling of dunes, scrub invasion at some sites and conversion of coastal dunes to other uses (golf courses, caravan sites, more permanent housing). This yields 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 a further x5 to estimate the true number of sites (and this seems a high estimate) we obtain 100 x 20 (10 confirmed sites plus an estimated 10 sites along the dunes of northern France) which gives 2000 mature individuals in total. The largest subpopulation along the north coast of France is estimated to comprise ca. 1000 mature individuals hence this species qualifies for VU rather than EN, but this should be reassessed when further georeferenced surveying has been carried out.
Two marram oyster species (Ainsworth et al. 2016) now recognised as present in France, UK and the Netherlands. 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. GBIF holds one New Zealand record of this species made in 2008 and originating from the redetermined collection PDD87504. This collection was found associated with Ammophila arenaria which is an introduced plant in New Zealand. Until there is evidence to the contrary, this is regarded as lying outside the natural range of this species and not considered in the assessment. There is also a 2019 Danish (Hirtshals øststrand) record of H. culmicola accompanied by a photograph which is possibly of H. bonii. This is, as yet, an unconfirmed record of H. bonii and so it was not considered in the assessment, but it was included on the distribution map as Denmark is very likely to be within the distribution range of this species.
6 sites known from UK (1 site known to have produced fruitbodies for two decades), but only seen on a few (<5) culms of Ammophila at each site. Four sites known from the Netherlands but described as a “characteristic species on the Northern French dune habitat (Guinberteau 2011). Possibly extinct in Ireland (no known records in the last 50 years).
Population Trend: Decreasing
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 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. bonii habitat. 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 (evidence noted at type locality, 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 is needed to inform practical conservation action. Management (cutting) of invasive Hippophae might be feasible for retention of partially invaded Ammophila habitat when the shrub is at early stage of encroachment. Control of mature Hippophae stands, on the other hand, is more likely to recreate a highly disturbed habitat which is then in a condition for new Ammophilla establishment and so may benefit H. bonii in the longer term. Further study is needed to study the effects of increased sand dredging on the relationship between accretion of coastal sand and shingle (pebbles) and to what extent this threatens H. bonii habitat and requires 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. bonii.
None currently known (although some culinary experimentation by wild food foragers is to be expected given the overall similarity to edible oyster mushrooms).
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