The classification was rank-based, using the ranks of class, subclass, order, suborder, family, subfamily and genus.
[1] The earlier system put forward by Smith et al. (2006) had suggested a range of 274 to 312 genera for ferns alone.
Defending PPG I, Schuettpelz et al. (2018) argue that the larger number of genera is a result of "the gradual accumulation of new collections and new data" and hence "a greater appreciation of fern diversity and [..] an improved ability to distinguish taxa".
[5] In response, Christenhusz and Chase (2018) argue that the excessive splitting of genera destabilises the usage of names and will lead to greater instability in future, especially when nuclear DNA is employed, and that the highly split genera have few if any characters that can be used to recognize them, making identification difficult, even to generic level.
They also argue that the new findings in phylogeny can easily be treated at subgeneric and subfamilial levels, so that the names used by non-specialists will remain unaltered.