An update of the revision of Cyathea subgen. Alsophila sect. Gymnosphaera (Cyatheaceae) in Madagascar and the Comoros including a discussion of putative hybridization events

A new revision of Cyathea sect. Gymnosphaera in Madagascar and the Comoros is proposed. Two new species, Cyathea impolita Rakotondr. & Janssen and C. rouhaniana Rakotondr. & Janssen, as well as a new variety, C. impolita var. michelii Rakotondr. & Janssen are described. As opposed to all other members of the section in the region, C. rouhaniana does not possess bullate scales nor a dense indument on the adaxial face of the costae and costulae; the fertile basal pinnae of each leaf are more rapidly caducous than the sterile pinnae and sori include abundant paraphyses longer than the sporangia. C. impolita and its variety michelii have dull, medium brown scales at their petiole base, isomorphic fertile and sterile pinnae and sori usually distributed over the entire abaxial surface in fertile leaves. The variety michelii differs from the typical variety by the presence of aphlebia. We provide original photos of the habit and trunk apex of each species that complement previously published descriptions. Putting more emphasis on soral paraphyses and lamina cutting for taxon delimitation allowed us to better circumscribe the three entities of the former C. bullata complex, now renamed to C. boiviniiformis, as well as to clarify the identity of C. poolii. A new key for determination and updated distribution maps are provided. Putative instances of hybridisation between closely related sympatric taxa are documented for the first time in Madagascan Cyatheaceae.