Abstract Molecular studies of sphagnicolous arrhenias in Newfoundland and Labrador created four clades in Arrhenia , three obligate sphagnophiles (two scaly-capped and one smooth-capped) and one facultative (smooth-capped). Nomenclatural review recovered 16 names applied to omphalinoid sphagnicolous taxa in the past. Critical review of these left five as suitable to this group. One scaly obligate sphagnophilic clade contained the type for Arr. gerardiana and the other the type for Clitocybe gerardiana var. fusca ; the latter we introduce as the novel species Arr. bigelowii . It differed from the first by longer spores and a darkening reaction in 10% of collections. The smooth-capped third obligate sphagnophilic clade contained the types of Ag. telmatiaeus and Omphalina fusconigra ; we recombined it as Arr. telmatiaea . This is the darkest species of the group, with a more northern distribution. The facultative sphagnophile was identified as Arr. philonotis , a lighter smooth-capped species also with a more northern distribution. In addition, we collected an unidentified smooth-capped facultatively sphagnophilic species of Omphalina of the O. pyxidata complex. All five species are distributed in both Europe and North America. We describe each species of Arrhenia with a sequenced type, providing new type material where needed, and add an informal description of the Omphalina . Overall, this study adds new sequences from 82 specimens of sphagnicolous arrhenias to the two existing in GenBank when we began, 11 new sequences of the unidentified species of Omphalina , and several other arrhenias.