Background and aims – Nautilocalyx pallidus is a broadly circumscribed species originally described from Peru under which several morphologically distinct taxa have historically been misidentified. As part of an ongoing taxonomic revision of Nautilocalyx, this study aims to re-evaluate the circumscription of N. pallidus, resurrect a species previously treated as a synonym, and describe a new species from Brazil.
Material and methods – The morphological analyses were based on herbarium specimens and field observations. Descriptions and measurements were derived from herbarium specimens, field images, and flowers preserved in alcohol. A preliminary conservation assessment for Nautilocalyx engelsii sp. nov. was conducted in accordance with the IUCN guidelines and criteria.
Key results – A species previously treated as a heterotypic synonym of Nautilocalyx pallidus is reinstated and transferred to Nautilocalyx as N. ochroleucus comb. nov., based on specimens from Brazil originally identified as Drymonia ochroleuca. This species differs from N. pallidus by its shorter stems, narrower leaves, longer floral bracts, and yellowish corolla. In addition, Nautilocalyx engelsii sp. nov. is described as a new species from the state of Mato Grosso, Brazil, and is characterized by green leaves suffused with red, entire and ciliate leaf margins, and a white corolla, suffused with pale pink outside. Lectotypes are designated for N. pallidus and N. hirsutus to clarify the application of these names.
Conclusion – This study clarifies the circumscription of Nautilocalyx pallidus and improves understanding of its species complex. As part of an ongoing taxonomic revision of the genus, we provide an updated circumscription, including an identification key, descriptions, illustrations, and field images. We recognize four species within the complex, redefine the morphological boundaries between N. hirsutus and N. pallidus, reinstate Nautilocalyx ochroleucus comb. nov., and describe a new species, Nautilocalyx engelsii sp. nov.