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Abstract Parablechnum cordatum (Blechnaceae) exhibits significant morphological variability, with many species considered as its synonyms, and is treated as a species complex by several authors. In this study, we offer a comprehensive revision of the taxon and an updated circumscription of Parablechnum usterianum, a species frequently confused with P. cordatum, leading to a refined understanding of species delimitation. Our analysis, based on morphological and spore micro- and ultrastructural examination of Brazilian specimens within the complex, recognizes three distinct species: Parablechnum cordatum s.s., Parablechnum brasiliense, and Parablechnum regnellianum, the latter being treated as a synonym but now resurrected with a new combination. Here, we present a key to the species, along with detailed descriptions, diagnostic images, distribution maps, lectotypifications, synonymies, and nomenclatural clarifications.

Abstract Fern spores play a vital role in dispersal. The unique features of spores, such as size, thickness, and ornamentation can aid in taxonomic decisions and division of groups. Moreover, certain species of ferns possess green spores containing chlorophyll, an uncommon feature that can reinforce the evidence of relatedness within a specific group. Lomaria spannagelii is a Neotropical species endemic to Brazil, and, even though green spores have been reported in its sister species, Lomaria nuda and Lomaria discolor, the presence of these spores has not yet been investigated in L. spannagelii. In this study, we investigated the morphology of L. spannagelii spores and sporangia, and, additionally, we determined the chromosome count of the species. Our results showed that the analyzed species has green spores, a characteristic shared with L. nuda and L. discolor, and has 2n = 64 chromosomes. This discovery provides new insights into this fern genus and emphasizes the importance of spore color and chromosome count in systematic and evolutionary studies of ferns.