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Evolution of resinous dots in the fern genus Elaphoglossum (Dryopteridaceae) and the systematics of the Elaphoglossum petiolatum complex

Martinez-Becerril, Ana Gabriela1; Vasco, Alejandra2

Published May 25, 2026 on Dryad. https://doi.org/10.5061/dryad.tb2rbp0hr

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Abstract

Elaphoglossum is one of the most species-rich fern genera, yet species delimitation is challenging because diagnostic characters are few and often require microscopy. Morphological study has nonetheless been central for distinguishing closely related taxa and informing phylogenetic hypotheses. The Elaphoglossum petiolatum complex was informally defined within E. sect. Lepidoglossa subsect. Pilosa by the presence of resinous dots on leaves and/or petioles, black rhizome scales with entire margins, and scales on the proximal portion of the petiole with dark-apices. Earlier molecular phylogenetic analyses suggested that the complex is not monophyletic and that all Mexican representatives form a clade (the Mexican-petiolatum clade), challenging both the definition of the complex and the homology of its diagnostic characters. To clarify the evolutionary history of resinous dots, evaluate relationships among species of the E. petiolatumcomplex, and test the monophyly of the Mexican-petiolatum clade, we conducted maximum likelihood analyses using three non-coding chloroplast spacers (atpβ–rbcL, rps4–trnS, trnL–trnF). Our sampling included nine of the 11 species of the complex, 43 Mexican species, 37 taxa with resinous dots, and totaled 176 Elaphoglossum taxa. Our analyses show that resinous dots evolved independently at least six times within sect. Lepidoglossa, and that the E. petiolatum complex is not monophyletic. Its species fall into three non-sister clades, here termed the Ciliatum (11 spp.), Lancifolium (20 spp.), and Petiolatum (7 spp.) clades. Although species with resinous dots are consistently present within these three clades, no single morphological character uniquely diagnoses any of them. Relationships within each clade remain poorly resolved, likely reflecting low plastid divergence and/or recent rapid diversification. Despite their repeated evolution, resinous dots remain informative for circumscribing the Ciliatum, Lancifolium, and Petiolatum clades, with implications for the circumscription of subsect. Pilosa and the E. petiolatum complex.