Cyclosorus is a genus of ferns in the family Thelypteridaceae (subfamily Thelypteridoideae, order Polypodiales), as circumscribed by the Pteridophyte Phylogeny Group's 2016 classification (PPG I). It was published by Link in 1833 (Hortus Regius Botanicus Berolinensis 2: 128) and is accepted in the GBIF backbone taxonomy, which currently lists 32 descendant taxa.
The genus's species limits are unsettled and vary widely by treatment. PPG I recognizes only about two species in a strict sense, while the Checklist of Ferns and Lycophytes of the World (as of January 2020) accepted a longer list of extant species but noted that only two to four of them likely belong in Cyclosorus sensu stricto, with the remainder needing eventual redistribution to other genera. At the broadest end, the online Flora of China treats roughly 250 species under Cyclosorus. Some authors instead sink the genus entirely into a very broadly defined Thelypteris, while others expand it to absorb genera that PPG I keeps separate. This makes Cyclosorus one of the more taxonomically contested fern genera, with its boundaries shifting substantially depending on which classification is followed.
The genus also has a fossil record, with species known from the Eocene of South China and the Quaternary of Australia, pointing to a long evolutionary history in the Old World tropics and subtropics. Among its recognized species are Cyclosorus interruptus and Cyclosorus striatus.
Etymology
The genus name Cyclosorus derives from Greek, referring to the circular sori (spore-bearing clusters) characteristic of its ferns.
Taxonomy Notes
Cyclosorus's species limits are disputed: PPG I (2016) recognizes only about two species sensu stricto, while the Checklist of Ferns and Lycophytes of the World (Jan 2020) accepted a longer list but judged only two to four of those as truly belonging in the genus, with the rest awaiting reassignment. Flora of China, by contrast, treats roughly 250 species under a much broader Cyclosorus, and some authors instead sink the genus into a broadly defined Thelypteris. GBIF's backbone taxonomy currently lists 32 descendant taxa. Fossil species attributed to the genus are known from the Eocene of South China and the Quaternary of Australia.
