Molecular studies of sphagnicolous arrhenias in Newfoundland and Labrador (NL) revealed four clades in Arrhenia, three obligate (two scaly capped and one smooth-capped) and one facultative (smooth-capped) sphagnophiles. Critical nomenclatural review of 16 names used for omphalinoid sphagnicolous taxa in the past left five suitable to apply to this group. One scaly capped 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 Agaricus telmatiaeus and Omphalina fusconigra; we recombined it as Arr. telmatiaea. This is the darkest species of the group, with a more northern distribution in NL. The facultative sphagnophile was identified as Arr. philonotis, a lighter smooth-capped species also with a more northern distribution in NL. Unexpectedly, we also 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. Overall, this study adds new sequences from over 80 specimens of sphagnicolous arrhenias to the two existing in GenBank when we began in 2006, 11 new sequences of the unidentified species of Omphalina, and several other arrhenias.