With the exception of angiosperms, the main euphyllophyte lineages (i.e. ferns sensu lato, progymnosperms and gymnosperms) had evolved laminate leaves by the Late Devonian, 385–360 million years ago. However, the evolution of laminate leaves remains unclear for early-diverging ferns. Wang et al. identify a novel fernlike taxon, Shougangia bella, from the Late Devonian that has laminate leaves on higher orders of vegetative and fertile branches. This fossil plant suggests that fernlike plants, along with other euphyllophyte lineages, had independently evolved megaphylls by the Late Devonian, possibly coinciding with rapidly declining levels of atmospheric CO2. The laminate pinnules of fernlike plants are homologous with planate ultimate appendages, and their fertile organs show an evolutionary increase in complexity.
Leaf evolution in early-diverging ferns
A novel fernlike taxon, Shougangia bella, is identified from the Late Devonian that has laminate leaves on higher orders of vegetative and fertile branches.