Isolated in biogeographic islands: discovery of a disjunct population of a fern in Northeastern Atlantic Forest

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Brejos Nordestinos (northeastern highland wet forests) is a unique ecosystem within the Northeastern Atlantic Forest. This area encompasses remmants of humid forests above 600 meters in the semi-arid region. These environmental conditions create an optimal ecosystem for the diversification of plants, including ferns. Pico do Jabre in Paraíba state, with an elevation of 1,208 meters above sea level, is an example of Brejo Nordestino. This study reports the occurrence of Pleopeltis pleopeltidis in the Northeastern Atlantic Forest, particularly at Pico do Jabre, a new record of P. pleopeltifolia for Paraíba state, and the local fern flora. Additional records of P. pleopeltidis were found in the municipalities of Triunfo and Floresta, in Pernambuco state, which are also classified as Brejos Nordestinos with elevations exceeding 1,000 m a.s.l. These findings extend the species known extent of occurrence by approximately 40%. The conservation status of P. pleopeltidis is suggested as Vulnerable (VU) across its entire range and Endangered (EN) in Northeast Brazil. The distance between populations in the Northeastern Atlantic Forest and the nearest populations in Bahia state ranges from 763–931 km, indicating a potential disjunction. Although the species occurs in three relatively close Brejos Nordestinos, the fragmented nature of the Northeastern Atlantic Forest results in isolated populations on these biogeographical islands, surrounded by a Caatinga (seasonally dry tropical forest) matrix.