The generic circumscription of Mrakia and Mrakiella: The proposal of Thomashallia gen. nov.

Abstract

In the family Mrakiaceae, the type genus Mrakia sensu stricto included five teleomorphic species with the type species, Mrakia frigida. In contrast, the anamorphic genus Mrakiella sensu stricto contained nine species with the type species, Mrakiella cryoconiti. Between the two genera, the completely separated clusters were shown respectively in the phylogenetic tree based on the 28S rRNA gene D1/D2 domain sequences derived from the neighbour-joining method. Between Mrakia frigida and Mrakiella cryoconiti as well as Mrakiella aquatica, the pair-wise sequence similarities were 98.6% and 97.4% (1.2% width) respectively. However, the similarities between Mrakia frigida and the remaining four Mrakia species were extreemely high (99.4 - 100% with 0.6% width). On the other hand, the similarity was relatively low (98.2%) between Mrakiella cryoconiti and Mrakiella aquatica, showing the wide range or the diversity of the anamorphic genus phylogenetically. The teleomorphic genus Thomashallia was newly introduced based on the formation of basidia and basidiospores with the type species, Thomashallia stelviica. The genus Krasilnikovozyma contained four species with the type species, Krasilnikovozyma curviuscula. Thus, the three teleomorphic genera were respectively taxonomic homogeneous-natured, and the three were characteristic of Q-8.