<i>Armillaria mexicana</i>, a newly described species from Mexico

<p><i>Armillaria mexicana</i> (Agaricales, Physalacriaceae) is described as a new species based on morphology, DNA sequence data, and phylogenetic analyses. It clearly differs from previously reported <i>Armillaria</i> species in North, Central, and South America. It is characterized by the absence of fibulae in the basidioma, abundant cheilocystidia, and ellipsoidal, hyaline basidiospores that are apparently smooth under light microscope, but slightly to moderately rugulose under scanning electron microscope. It is differentiated from other <i>Armillaria</i> species by macromorphological characters, including annulus structure, pileus and stipe coloration, and other structures. DNA sequence data (nuc rDNA internal transcribed spacers [ITS1-5.8S-ITS2 = ITS], 28S D-domain, 3′ end of 28S intergenic spacer 1, and translation elongation factor 1-α [<i>TEF1</i>]) show that <i>A. mexicana</i> sequences are quite distinct from sequences of analogous <i>Armillaria</i> species in GenBank. In addition, sequences of ITS of the <i>A. mexicana</i> ex-type culture reveal an ITS1 of 1299 bp and an ITS2 of 582 bp, the longest ITS regions reported thus far in fungi. Phylogenetic analysis based on <i>TEF1</i> sequences place <i>A. mexicana</i> in a well-separated, monophyletic clade basal to the polyphyletic <i>A. mellea</i> complex.</p