Rodriguésia 74: e00492023. 2023 http://rodriguesia.jbrj.gov.br DOI: http://dx.doi.org/10.1590/2175-7860202374064 Abstract Athyrium decurtatum var. platense (= Thelypteris decurtata subsp. platensis) is transferred to the genus Amauropelta and raised to the species level based on morphological, palynological and geographical evidences. This fern species is endemic to the Delta of Paraná district, belonging to the Esteros del Iberá biogeographic province in the Southern Cone of South America. Key words: Amauropelta, Argentina, endemism, ferns, Uruguay. Resumo Athyrium decurtatum var. platense (= Thelypteris decurtata subsp. platensis) é transferida para o gênero Amauropelta e elevada ao nível de espécie com base em estudos morfológicos, palinológicos e geográficos. Esta espécie é endêmica do distrito Delta do Paraná, pertencendo à província biogeográfica dos Esteros del Iberá, no Cone Sul da América do Sul. Palavras-chave: Amauropelta, Argentina, endemismo, samambaias, Uruguay. Ferns and Lycophytes as new challenges Amauropelta platensis (Thelypteridaceae), a new combination for the endemic Southern Cone fern flora Pedro Cayetano Berrueta 1,4 , Marta Mónica Ponce 2 , María Luján Luna 1,5 , Gabriela Elena Giudice 1,6 & Marcelo Daniel Arana 3,7 1 Universidad Nacional de La Plata, Facultad de Ciencias Naturales y Museo, Laboratorio de Anatomía Comparada, Propagación y Conservación de Embriofitas “Dr. Elías de la Sota”, La Plata, Argentina. 2 Instituto de Botánica Darwinion, IBODA-CONICET, San Isidro, Buenos Aires, Argentina. ORCID: <https://orcid.org/0000-0002-5809-6549>. 3 Universidad Nacional de Río Cuarto, Instituto ICBIA (UNRC-CONICET), Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Departamento de Ciencias Naturales, Grupo GIVE, Río Cuarto, Córdoba, Argentina. ORCID: <https://orcid.org/0000-0001-7921-6186>. 4 ORCID: <https://orcid.org/0000-0001-7296-8019>. 5 ORCID: <https://orcid.org/?0000-0001-7025-782X>. 6 ORCID: <https://orcid.org/0000-0003-1352-4009>. 7 Author for correspondence: marana@exa.unrc.edu.ar Thelypteridaceae is one of the largest families of ferns, cosmopolitan in distribution with more than 1,200 species highly diverse morphologically and ecologically (Fawcett & Smith 2021), inhabiting mainly tropical and subtropical regions of the world (Smith 1992; Smith et al. 2006, 2008; PPG I 2016). As usually construed, the family is monophyletic and recent molecular phylogenetic studies have recovered two main groups: the phegopteroid and the thelypteroid lineages (Smith & Cranfill 2002; He & Zhang 2012; Almeida et al. 2016; Fawcett & Smith 2021), which are recognized at subfamily level (PPG I 2016). In the subfamily Thelypteridoideae (thelypteroid lineage), the amauropeltoid clade comprises the genera Amauropelta Kunze, related to the genera Coryphopteris Holttum, and Metathelypteris (H.Itô) Ching (Almeida et al. 2016; Fawcett & Smith 2021; Fawcett et al. 2021). Amauropelta Kunze is a genus morphologically circumscribed by the base of the lamina gradually or abruptly reduced, with one-to- many pairs of auriculiform or glanduliform pinnae, the veins from adjacent segments usually meeting at the blade margins above the sinuses on pinnatifid pinnae, and sporangia either rarely or not setose (Ponce 1995; Salino et al. 2015; Ponce & Zanotti 2018; Fawcett & Smith 2021). Amauropelta is characterized also by the spore wall with reticulate ornamentation (Ponce 1987). According to Fawcett & Smith (2021), Amauropelta is distinguished from Metathelypteris (eastern Asia) by characters as veins running to the margins, adaxially grooved costae and a base chromosome number of x = 27, 29, 31 (vs. usually x = 35 in Metathelypteris). From Coryphopteris, Amauropelta differs by the combination of usually greatly reduced proximal