Phylogenetic placement of two taxonomically controversial South American spleenworts with unusual morphology: Asplenium brasiliense Sw. and Asplenium douglasii Hook. & Grev. (Aspleniaceae)

The genus Asplenium is known for its high morphological diversity and complex evolutionary history. Two South American species, Asplenium brasiliense and A. douglasii , possess unusual morphological traits, including simple fronds, anastomosing venation, and paired indusia opening toward each other, which have historically led to their assignment to several satellite genera, such as Antigramma , Hemidictyum , Phyllitis , and Scolopendrium . However, their phylogenetic positions have never been rigorously tested using molecular data. In this study, four chloroplast markers were employed to infer the phylogenetic placement of these two enigmatic species. The phylogenetic analyses robustly resolved both species as members of the Asplenium schaffneria clade, where they form a strongly supported monophyletic group that is sister to the A. varians subclade. This study provides the first molecular phylogenetic evidence clarifying the phylogenetic relationships of A. douglasii and A. brasiliense , demonstrating that their morphological peculiarities represent specialized evolutionary derivations within Asplenium s.l. rather than providing justification for generic segregation.