Systematics of the genus Auricularia with an emphasis on species from the southeastern United States.

The genus Auricularia comprises 10–15 recognized species worldwide, and most are considered to have intercontinental to cosmopolitan distributions. Though regional field guides for the southeastern United States treat only one or two species, five species, A. fuscosuccinea, A. auricula-judae, A. mesenterica, A. polytricha, and A. delicata , have been recorded from the region. This study seeks to evaluate and revise current species concepts in Auricularia using phylogenetic and morphological methods to better understand the species occurring in the southeastern United States. Historical collections from herbaria and fresh material from the field have been examined and sequenced at two loci, ITS and rpb2. Phylogenetic results indicate several diverse clades are in need of taxonomic revision. Previous reports of A. auricula-judae in the southeastern U.S. likely represent a clade of A. americana . Collections identified as A. delicata are found to be polyphyletic and distributed in four clades. Variation in the presence or absence of a medulla layer in some species, previously a key morphological character, has made it evident that additional characters are required to reflect the genetic diversity in the genus. A new taxonomic character, the schizomedulla, is discussed and shown to distinguish two novel species, A. subglabra and A. scissa , from the morphologically similar species A. delicata . A reticulate, merulioid hymenial surface can no longer be considered a character unique to A. delicata . Furthermore, ITS data from the voucher-specimen from which the genome of A. delicata was produced indicates this species is A. subglabra . The taxonomy and nomenclature of Peziza nigricans is discussed and it is shown to be the earliest priorable name for A. polytricha sensu auct. amer. , and the new combination Auricularia nigricans is proposed. We now recognize the following species of Auricularia from the southeastern U.S.: A. americana, A. fuscosuccinea, A. mesenterica, A. nigricans, and A. scissa.