Stasis and convergence characterize morphological evolution in eupolypod II ferns.

Area of Science:

• Evolutionary biology
• Plant morphology
• Phylogenetics

Background:

• Morphological evolution above family rank in ferns is underexplored.
• Eupolypod II ferns, comprising one-third of species, show complex phylogenetic patterns.
• Traditional classifications of 'athyrioid' ferns are challenged by molecular data.

Purpose of the Study:

• To analyze morphological characters in eupolypod II ferns to understand evolutionary patterns.
• To test hypotheses of evolutionary stasis versus convergent evolution in fern phylogeny.
• To reappraise character concepts for future fern morphology studies.

Main Methods:

• Analysis of 79 morphological characters across 81 eupolypod II fern taxa.
• Maximum-likelihood and maximum-parsimony character optimizations on a molecular phylogeny.
• Phylogenetic signal testing using randomization methods and fitdiscrete.

Main Results:

• Most character state changes occur at or above the family level in eupolypod II ferns.
• Petiole vasculature with two bundles is ancestral for eupolypods II.
• A chromosome base number of x=41 is identified as synapomorphic for all eupolypods.

Conclusions:

• Integrated morphological and phylogenetic data clarify evolution in eupolypod II fern families.
• Sorus position provides strong support for a recently identified clade (Aspleniaceae, Diplaziopsidaceae, Hemidictyaceae, Rachidosoraceae).
• The study establishes the ancestral state for chromosome number in the eupolypod clade, a significant finding for fern evolution.