ABSTRACT: Fourteen additional species of Haplotrichum are described and illustrated, bringing the number treated by the authors to twenty-nine. An account of the respective distinguishing characteristics of each is presented. They include five taxa which are being transferred into the genus, and one novel species. In accordance with a genus-for-genus philosophy, Allescheriella is considered a synonym. Further commentary is made on the considerable morphological variation existing within the genus and among individual species of apparently close phylogenetic affinity. A revised treatment of H. curtisii is provided to more adequately document the apparent phenotypic plasticity of this entity. A nomenclatorial addendum to fully list H. capitatum synonymies is included, and a key to all thirty-two species known is furnished.

KEYWORDS: Alescheriella, Botryobasidium anamorphs, Oidium, species concepts

NOMENCLATURAL NOVELTIES:
Haplotrichum armeniacum (Berk. & M.A. Curtis) Partridge & Morgan-Jones, p. 44
Haplotrichum croceum (Mont.) Partridge & Morgan-Jones, p. 51
Haplotrichum laevisporum (Cooke) Partridge & Morgan-Jones, p. 63
Haplotrichum morganii (Linder) Partridge & Morgan-Jones, p. 70
Haplotrichum ponderosum Partridge & Morgan-Jones, p. 75
Haplotrichum pulveraceum (Ellis) Partridge & Morgan-Jones, p. 79