We summarize results of two independent ethnobiological field studies in adjacent Zapotec towns in the Sierra de Miahuatlán, Oaxaca, Mexico. San Juan and San Pedro Mixtepec share a common language (with minor lexical variation) and occupy contiguous traditional municipal territories ranging from 1650 m to 3700 m elevation and practice a common subsistence agricultural tradition. In conjunction, our data provide a detailed account of how macro-fungi are classified, named, and used by residents of these two towns. We first consider “where fungi fit” in the local worldview as well as in the broader context of folk systematics, noting their relative neglect in ethnobiological studies to date. We document more than 30 distinct, named folk generic taxa of macro-fungi (known locally as mĕy), analyze the nomenclatural patterns characteristic of this life-form, and argue that it is best construed to be “an unaffiliated life-form” rather than an unaffiliated folk generic taxon or a kingdom on a par with that of plants or of animals. We briefly characterize the ecology and phenology of each recognized folk taxon and detail how 25 species are used as food. We note in particular how local harvesters distinguish confusingly similar toxic from edible species. We compare the Mixtepec Zapotec classification and nomenclature with that of two other Mexican Indigenous societies, the Purépecha of Michoacán, and the Tzeltal Maya of Chiapas, noting many similarities but also some intriguing contrasts.