Phylogenetic relationships of two Cuban spleenworts with unusual morphology: Asplenium (Schaffneria) nigripes and Asplenium pumilum (Aspleniaceae, leptosporangiate ferns)

Abstract

The infrageneric classification of Asplenium, the most species-rich genus of ferns, is notoriously difficult as a result of extensive morphological homoplasy combined with exceptional morphological disparity. Besides a core Asplenium, 29 satellite genera have been described, but most of them have not been widely accepted. In recent years, molecular phylogenetic studies found most of these satellite genera to be nested in Asplenium, but several morphologically distinct taxa have not yet been included in such studies. One of these elements is the monospecific neotropical genus Schaffneria which is characterized by undivided suborbicular blades, lack of a costa, black stipes, netted veins and single or paired sori. Maximum likelihood and Bayesian phylogenetic inference based on the chloroplast DNA markers rbcL, rps4, rps4-trnS and trnL-trnF indicated a position of Schaffneria nigripeswithin Asplenium. We thus propose to treat Schaffneria as a synonym of Asplenium and adopt the name Asplenium nigripes. With the current sampling, Asplenium (Schaffneria) nigripes is placed sister to A. pumilum, the only species of Asplenium with whitish catenate hairs on its leaves. Despite considerable morphological differences, both species resemble each other in several features including filiform-lanceolate, mostly entire, brown-blackish rhizome scales with a dark-sclerotic center and some marginal projections, a striate, hairy epidermis, echinolophate spore ornamentation with slim microechinate folds forming small lacunae, and Aspidium-type gametophytes.