Hymenomycetes was formerly the largest taxonomic group of fungi within the division Basidiomycota, but the term is no longer taxonomically relevant.
[1] This class contained the orders Agaricales, Boletales, and Russulales.
The erstwhile class, now understood to be a polyphyletic assemblage of basidiomycetes, refers to fungi with fruit bodies whose hymenophore develops in an exposed manner, or only with a veil (velum).
These forms are termed gymnocarpic or hemiangiocarpic ontogeny, respectively.
A contrasting example of hymenophore development is the puffballs, which undergo gasterocarpic development (hymenophore enclosed).