Suggested as Data Deficient (DD).
There are few current sites known, but the albeit infrequent collections have been reliably identified from two continents and from Alnus hosts with a broad geographical range, which elevates the estimated number of sites where B. bartholomaei might occur to 30,000. Further targeted surveys within the range of it’s Alnus host will be required to determine numbers of mature individuals.
Hypoxylon bartholomaei Peck
Nummulariola bartholomaei (Peck) P.M.D. Martin
Nummularia bartholomaei (Peck) Lar.N. Vassiljeva
The type collection was made in 1909 at Rolling Bay WA, on Alnus rubra. The fungus is somewhat similar in appearance to B. nummularia, which is predimanately a European species, but differs in ascospore size and the robust white conidial state that develops under the bark before it is pushed off by the emerging stromata.
This large, black, flat pyrenomycete (ascomycete) fruits in massive clusters often several meters long on dead and dying Alnus, and causing large areas of bark to fall off and the trunks taking on a “leopard spot” appearance. However, it has only been observed and reported a small number of times in the Pacific Northwest and the Russian far east. It is not known from any other regions in the world, and was not encountered during 45 years of general forest disease surveys in western Canada. Further targeted surveys within the range of its Alnus host will be required to determine numbers of mature individuals.
Current known distribution is the Pacific Northwest, and the Russian Far East. Found to date in coastal Alnus rubra stands on southern Vancouver Island, British Columbia Canada. In the United States from western Washington state (Alnus rubra and Populus trichocarpa, but the latter host record should be confirmed), and northern Idaho (Alnus tenuifolia). Also collected in the Russian Far East, in the Kamtchatka peninsula, on Alnus kamschatia. Described by Vassiljeva (2009) as having a northern amphipacific or “Bering disjunction” in its global distribution.
There are less than 20 collections made of this species worldwide, from approximately 10 different sites. In the United States it is known from the type collection made in 1909 at Rolling Bay WA, and another 1909 collection at nearby Bainbridge Island, WA, Kitsap County, all on Alnus rubra. There are two other collections from Washington State, one in Sequim in 1901 on Populus trichocarpa (an unusual host, which should be confirmed), and another in Snohomish County on Alnus rubra. It is also known from a coastal site in Oregon, Cape Perpetua, Lincoln Co. in 2015, on Alnus rubra.
The first Canadian record of B. bartholomaei was collected on Southern Vancouver Island in 1995 on Alnus rubra. Since then it has been observed in 3 nearby decadent Alnus rubra stands located in the southern tip of Vancouver Island, BC, but nowhere else in Canada.
A separate host association is reported from two locations in Northern Idaho, collected in 1922, and 2004 on Alnus tenuifolia, at higher altitudes.
It has also been collected from the Russian Far East on the Kamtchatka peninsula, on Alnus kamschatia.
As the clustered fruitings on exposed wood are often large and showy and especially visible in winter and early spring before leaves develop on surrounding vegetation, it seems unlikely that the species is overlooked when found. In the Pacific Northwest in particular, there are no other pyrenomycete species with the same combination of morphology and habit where it occurs on mature decadent Alnus rubra in coastal stands.
Taking into account that there are 10 known sites worldwide, we estimate that 30 trees per site will bear fruiting bodies, because the tree groves bearing the fungus usually have several infected trunks due to close proximity. Adding a factor of 10 ramets per tree due to high genetic diversity in stromata as demonstrated in other Biscogniauxia species (Henriques et al 2014), the disjunct distribution, the host range of Alnus contiguous with known sites, and allowing the total number of sites to be 10 times higher to allow for those yet undiscovered, we estimate the total number of mature individuals of B. bartholomaei to be 30,000.
Information on the full extent of the population is too sparse to evaluate a trend, apart from the potential for habitat loss.
Population Trend: Uncertain
The fungus causes a white rot of alder wood, on branches and trunks of host trees, where the black stromata develop under the bark and force the bark off in large sheets. In coastal regions of the Pacific Northwest, it has been found on large, overmature trees with broken tops. Biscogniauxia species are known to be saprophytic, i.e. causing wood decay and persisting to produce fruiting bodies for years after tree death on fallen logs, but they also opportunistic parasites, causing bark loss and cankers on standing live trees stressed by environmental factors such as drought stress or top breakage from weather events (Edwards, 2003). Therefore the fungus might be less prevalent in healthy stands, and more prevalent on the boundaries of natural distrubution of the tree hosts where they are more likely to be physiologically stressed, for example in sites prone to drought or at high altitudes or coastal decadent stands stressed by soil erosion and winter storms.
In coastal Pacific Northwest sites, reduction of habitat due to urbanization. As Alnus is the preferred host for B. bartholomaei, there is potential risk of habitat destruction by the oomycete Phytophthora alni Brasier and S. A. Kirk , a virulent pathogen of alder, if it were introduced. Alnus rubra is highly susceptible to this pathogen (Downing et al. 2010).
On Vancouver Island, British Columbia, two of the known sites occur in parks or other controlled access sites (military base), so some degree of protection is afforded to these populations.
-Further collections to better delimit the full range of the fungus in coastal North America, determination of host tree species range within the genus Alnus
- Plot based surveys to estimate number of stands affected, and number of stems in affected stand.
- Comparison of high altitude Idaho collections on Alnus tenuifolia to coastal collections on A. rubra; determination of genetic relatedness of these populations
Callan, B. 2000. Two web-accessible fungus databases and their relationship to a preliminary list of rare macrofungi for British Columbia. Pp. 109-112 in: Darling, L. (ed.). Proceedings of a conference on the biology and management of species and habitats at risk. Kamloops, BC. 15-19 Feb. 1999, Volume One. BC Ministry of Environment, Lands, and Parks, Victoria, BC. and University College of the Cariboo, Kamloops, BC.
Downing, M, Jung, T., V., Blasch, M., Tuffly, M.F. and Reich, R. 2010. Estimating the Susceptibility to Phytophthora alni Globally Using Both Statistical Analyses and Expert Knowledge. pp. 559-570 in: Advances in Threat Assessment and Their Application to Forest and Rangeland Management General Technical Report PNW-GTR-802.
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Vasilyeva L.N. 1988. The taxonomic position of Camarops polysperma (Mont.) J.H. Miller and Biscogniauxia O. Kuntze in the Far East. Mikologiya i Fitopatologiya 22: 388–396 (in Russian).
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