Systematics of Hypocrea citrina and related taxa.

Morphological studies and phylogenetic analyses of DNA sequences from three genomic regions - the internal transcribed spacer (ITS) regions of the nuclear ribosomal gene repeat, a partial sequence of RNA polymerase II subunit (rpb2), and a partial sequence of translation elongation factor (tef1) - were used to investigate the systematics of Hypocrea citrina and related species. A neotype specimen is designated for H. citrina that conforms to Persoon's description of a yellow effuse fungus occurring on leaf litter. Historical information and results obtained in this study provide the foundation for selection of a lectotype specimen from Fries's herbarium for H. lactea. The results indicate that (1) Hypocrea citrina and H. pulvinata are distinct species; (2) H. lactea sensu Fries is a synonym of the older name H. citrina; (3) H. pulvinata, H. protopulvinata, and H. americana are phylogenetically distinct species that form a well-supported polyporicolous clade; (4) H. citrina is situated in a clade closely related to H. pulvinata; and (5) H. microcitrina and H. pseudostraminea reside in a highly supported clade phylogenetically distinct from H. citrina. Hypocrea protopulvinata, H. microcitrina, H. megalocitrina, H. pseudostraminea, and a new species, H. aurantiistroma, are reported and described from North America. Variation in rpb2 and tef1 gene sequences suggests geographical subgroupings between European and North American isolates of H. pulvinata. The phylogenies inferred from ITS, rpb2, and tef1 gene sequences are concordant. Hypocrea citrina var. americana is elevated to species status, Hypocrea americana.