The Pteridophyte Phylogeny Group (PPG) is an informal international group of systematic botanists who collaborate to agree on the classification of pteridophytes that reflects knowledge about plant relationships discovered through phylogenetic studies. In 2016, the group published a classification for extant pteridophytes, termed "PPG I". The paper had 94 authors . The classification was presented as a consensus classification supported by the community of fern taxonomists. Alternative classifications of ferns exist and are preferred by some.