Creation of provisional species name Xylobolus sp. 'frustulatus-MA01'

This post is a part of a series outlining the rationale for the creation of provisional species names. For more information on provisional species names, see Stephen Russell's post here. To see other posts like this, check out the "Provisional Species Names" category in the sidebar. 

Xylobolus frustulatus is a common crust fungus that produces repeating tile-like, cracked fruiting bodies on hardwood logs. This is the reason behind the specific epithet "frustulatus", which derives from the Latin frustum or frustulum meaning "piece" or "part". ​Originally described as Thelephora frustulata by Christiaan Hendrik Persoon in 1801, the species was sanctioned by Elius Magnus Fries in 1821 and transferred to Xylobolus by Petter Adolf Karsten in 1881. European names are frequently applied to North American fungi, but DNA sequencing has shown time and again that they are often different species. This appears to be the case with Xylobolus frustulatus. 

Phylogenetic tree of Xylobolus ITS sequences from iNaturalist and GenBank. The sequences were aligned with MAFFT, trimmed with trimAl, analysed with IQ-TREE 3, and midpoint rooted and printed with ggtree in R. Ultrafast bootstrap support values greater than 95% are shown.

The Xylobolus ITS tree above shows a phylogenetic separation between Euroasian and North American Xylobolus frustulatus specimens, and the distance matrix below shows a clear ITS barcode gap as well. Since Xylobolus frustulatus was first described from Europe, I'm creating a provisional species name to refer to the North American clade: Xylobolus sp. 'frustulatus-MA01'. The code "MA01" refers to Massachusetts based on the origin of the oldest sequenced specimen on iNaturalist, one that I collected and barcoded years ago (iNaturalist172276632). Other sequenced specimens belonging to Xylobolus sp. 'frustulatus-MA01' can be explored here. I expect this is an undescribed species, but a more thorough investigation of type material and previously published names that might apply to this clade are required. 

Distance matrix and heatmap of ITS pairwise percent similarity in the Xylobolus frustulatus group.