Imaia, a new truffle genus to accommodate Terfezia gigantea.

Originally described from Japan by Sanshi Imai in 1933, the hypogeous ascomycete Terfezia gigantea was subsequently discovered in the Appalachian Mountains of the USA. Morphological, electron microscopic, and phylogenetic studies of specimens collected in both regions revealed that, despite this huge geographic disjunction, (1) the Japanese and Appalachian specimens are remarkably similar both in morphology and the sampled rDNA sequences, (2) the species unambiguously falls into the Morchellaceae and is separated from the genus Terfezia in the Pezizaceae, (3) its spores are much larger than those of Terfezia spp. and are enclosed in a unique, electron-semitransparent, amorphous epispore that appears to be permeated with minute, meandering strands or canals. In addition to the molecular phylogenetic results, the numerous nuclei in ascospores, the dome shaped, striate ascus septal plugs and the long cylindric Woronin bodies also strengthen the family assignment to the Morchellaceae. Moreover, the species occurs in moist, temperate forests as opposed to the xeric to arid habitats of other Terfezia spp. We propose the new, monotypic genus Imaia to accommodate the species.