Cryptocaulaceae: a new and deeply diverged branch within the fern tree of life.

Advances in phylogenomics have greatly clarified fern evolutionary relationships, yet significant gaps remain. In this study, we performed phylogenetic and phylogenomic analyses of Polypodiineae, one of the most species-rich suborders of Polypodiales, and found that Tectaria tenerifrons is a deeply diverged lineage. Our results support it as sister to Nephrolepidaceae in the plastome dataset, whereas the transcriptome dataset recovered it as sister to a clade comprising Nephrolepidaceae, Polypodiaceae, Davalliaceae, Oleandraceae, Tectariaceae s.l. No results support it as a member of the Tectariaceae, where it was previously classified. To reflect this deep divergence, we establish a new family, Cryptocaulaceae fam. nov., and a new monotypic genus, Cryptocaulon gen. nov, and propose the new combination Cryptocaulon tenerifrons comb. nov. Morphologically, Cryptocaulon can be distinguished from Tectaria by a combination of characters: long-creeping carnose rhizomes; subclathrate scales with multicellular hairs; anastomosing venation forming multiple rows of areoles without free included veinlets; basal veinlets of pinna lobes on the basiscopic side arising from the pinnule costule; cristate perispores with short, thick ridges; basic chromosome number, x = 41. We also designated a lectotype for C. tenerifrons.