Mollisia
is a taxonomically neglected discomycete genus (
Helotiales, Leotiomycetes
) of commonly encountered saprotrophs on decaying plant tissues throughout temperate regions. The combination of indistinct morphological characters, more than 700 names in the literature, and lack of reference DNA sequences presents a major challenge when working with
Mollisia
. Unidentified endophytes, including strains that produced antifungal or antiinsectan secondary metabolites, were isolated from conifer needles in New Brunswick and placed with uncertainty in
Phialocephala
and
Mollisia
, necessitating a more comprehensive treatment of these genera. In this study, morphology and multigene phylogenetic analyses were used to explore the taxonomy of
Mollisiaceae
, including
Mollisia
,
Phialocephala
, and related genera, using new field collections, herbarium specimens, and accessioned cultures and sequences. The phylogeny of
Mollisiaceae
was reconstructed and compared using the nuc internal transcribed spacer rDNA (ITS) barcode and partial sequences of the 28S nuc rDNA (LSU) gene, largest subunit of RNA polymerase II (
RPB1
), DNA topoisomerase I (
TOP1
), and the hypothetical protein Lipin/Ned1/Smp2 (
LNS2
). The results show that endophytism is common throughout the
Mollisiaceae
lineage in a diverse range of hosts but is infrequently attributed to
Mollisia
because of a paucity of reference sequences. Generic boundaries within
Mollisiaceae
are poorly resolved and based on phylogenetic evidence the family included species placed in
Acephala
,
Acidomelania
,
Barrenia
,
Bispora
,
Cheirospora
,
Cystodendron
,
Fuscosclera
,
Hysteronaevia, Loramyces, Mollisia, Neopyrenopeziza
,
Obtectodiscus, Ombrophila, Patellariopsis
,
Phialocephala
,
Pulvinata
,
Tapesia
(=
Mollisia
), and
Trimmatostroma.
Taxonomic novelties included the description of five novel
Mollisia
species and five novel
Phialocephala
species and the synonymy of
Fuscosclera
with
Phialocephala
,
Acidomelania
with
Mollisia
, and
Loramycetaceae
with
Mollisiaceae
.