Below are lists of extant fern families and subfamilies using the classification scheme proposed by the Pteridophyte Phylogeny Group in 2016 (PPG I). [1] The scheme is based on molecular phylogenetic studies, and also draws on earlier classifications, [1] particularly those by Smith et al. (2006), [2] Chase and Reveal (2009), [3] and Christenhusz et al. (2011). [4] It rejects the very broad circumscription of some families used by Christenhusz and Chase (2014), whose Aspleniaceae corresponds to the entire suborder Aspleniineae of PPG I. [1] [5]