A revision of the fern family Cyatheaceae in the Mascarene Islands

Based on the examination of herbarium specimens including numerous recent collections and on observations of the species in situ, we herein present a revision of the tree fern family Cyatheaceae for the Mascarene Islands. Three taxa are accepted for Réunion, two of which are endemic to the island. Four taxa, including one endemic species and two endemic varieties, are recognized for Mauritius. One introduced species is present on both islands. We describe one new species, Cyathea grangaudiana Th.Janssen & Rakotondr. and one new variety, Cyathea borbonica Desv. var. sevathiana Th.Janssen & Rakotondr. from Mauritius. Cyathea grangaudiana has a pinnate-pinnatisect lamina, scattered acicular hairs on the abaxial face of the costules and sporangiasters on the receptacle. Cyathea borbonica var. sevathiana has erect leaves, a bipinnate lamina with conduplicate pinnae and pinnules as well as smaller and more coriaceous pinnules than the type variety. We comment on the usage of ancient names having led to taxonomic confusion in the past, and discuss the status of doubtful taxa. Sporangiasters, sterile sporangiform structures on the receptacle, are documented for two species from Mauritius. In order to facilitate field identifications, we include in our treatment a complete illustration of each taxon as well as two different identification keys one of which is largely based on characters readily observable in the field.