Anatomical Studies of Brazilian Amazonian Isoëtes Species: Inferences on Habitat Adaptation

Abstract Isoëtes is a cosmopolitan genus of aquatic lycophytes, containing more than 200 species. In Brazil, the genus comprises 29 species, with three occurring in Pará state, Amazon. Isoëtes cangae and I. serracarajensis are endemic to the ferruginous outcrops of Serra dos Carajás, and I. amazonica occurs on the inundated shores of the Tapajós River. Despite the great diversity of quillworts in South America, their anatomy remains unknown. This study discusses Brazilian Amazon species’ leaf and root anatomical traits in relation to habitat and genetic diversity. The amphibious I. amazonica and I. serracarajensis were observed to have similar stomata and cuticular ornamentations. Isoëtes cangae, a fully aquatic species, had smaller epidermal cells and a smooth cuticle and showed slight differences regarding the lacuna diaphragm. The genetically closer species from Carajás both lacked peripheral fiber strands on the leaves. Our study complements current knowledge regarding the morphoanatomy of Amazonian species and provides a better understanding of their biology, contributing to the development of conservation strategies for these species.