Taxonomic richness of lycophytes and ferns of the Mexican beech forest: Highest ever recorded among Fagus forests worldwide?

•Mexican beech forests have a high richness of lycophytes and ferns per area unit.•The structural importance value of the fern species differed among localities.•The environmental in the Fagus forest favored to presence of lycophytes and ferns.•Floristic composition among localities with beech forests was relatively similar.

The composition, richness and distribution of fern and lycophyte species were studied in the three largest and most intact stands of the beech Fagus grandifolia subsp. mexicana in Mexico, located in the Sierra Madre Oriental (SMO) in the state of Hidalgo. During fieldwork, specimens were collected in these stands, and five 60 m2 sampling plots were also selected in order to estimate the relative importance value (RIV) of the species at each locality. Floristic similarity between localities was calculated based on species absence/presence data, and richness was estimated as a measure of plant biodiversity. In both analyses, data from previous studies in different regions of the SMO were included. In total, 21 families, 49 genera and 82 species of ferns and lycophytes were recorded for the beech forest of the state of Hidalgo; five of those species fall under a risk category according to Mexican legislation. Most species had either terrestrial or epiphytic habit. The species with high RIV differed among localities, except for Lophosoria quadripinnata which was dominant at all three localities. Our results indicate that Mexican Fagus forests have a higher richness of lycophyte and fern species per unit area than any other Fagus-dominated forests in the world. Thus, conservation and management programs should be implemented in the short term, in view of the limited area occupied by these forests and the constantly increasing levels of human-generated disturbance.