Xerocomus chrysenteron - cisalpinus

In 1968 Ross McNabb published a revision of our boletes in the New Zealand Journal of Botany, volume 6, pp137-176. In that revision he noted for the first time the occurrence of Xerocomus chrysenteron, the red-cracked bolete, as an ectomycorrhizal associate of a number of introduced broad-leaf trees. In the years since a number of similar looking fungi have also been reported such as Xerocomus pruinatus, X. badius and X. porosporus and I thought I had collected a number of them. Relatively recently in Europe molecular work has clarified species concepts in the group. As part of recent work towards a new revision of our boletes many of my collections in this group were sequenced. Very surprisingly nearly all the collections of different 'species' sequenced so far correspond to just a single recently described (recognised) species, X. cisalpinus. This was described from Italy and subsequently found in other European countries. The variability we have for this species seems to exceed that reported in its home territory and may explain some of the reports of other species in NZ (it certainly misled me). These could still turn out to be different species with very similar 'barcode' sequences, but what is certain is that they are not the same as the European X. chrysenteron , X. pruinatus, X. porosporus or X. badius and the appropriate name is X. cisalpinus.

It is quite hard to distinguish our variable X. cisalpinus from related species but the consistent character is the faint striations on the spores. It can only be seen using an oil immersion objective at 1000x, and even then when the spore is oriented at just the right angle (or using Differential Interference Optics).But if a lot of spores are viewed the striations are usually quite apparent. Sequencing has confirmed we do also have some other related species, specifically X. ripariellus and X. bubalinus. If the spores are truncated (only observable on mature spores) then X. porosporus is a possibility but there are no confirmed records so far.

The Large Subunit tree with all these species is attached to ...
https://inaturalist.nz/observations/1390152