Hidden in the mountain: a new rare Syagrus (Arecaceae) with morphological novelties

Background and aims – The Serra do Ambrósio is a mountain with a unique vegetation called carrasco . The carrasco is characterised by sandy soils of high granulometry and is home to rare species. During the current research on the Arecaceae flora of the Diamantina Plateau, a new Syagrus species was discovered, which is described here. Material and methods – The morphology and anatomy are described based on field collections. The pinnae anatomy was analysed using LM (free-hand cross sections). The new species belongs to the Syagrus glaucescens complex, and an identification key and a distribution map were created. Key results – Syagrus harenae resembles S. glaucescens , but some characteristics easily differentiate it, such as the small size, lax pinnae, symmetric pinnae tips, ramenta scales, a scattered thin indumentum on the peduncle, inflorescences and fruits orangish-yellow, and pistil with indumentum. The new species also possesses flowers arranged in tetrads and pentads and is the first species of Syagrus showing two sepals, petals with imbricate tips, staminodes with anthers, and frequently lacks staminodial rings. The pinnae anatomy of the new species also resembles S. glaucescens , which indicates their relatedness. However, reliable differences in pinnae anatomy set the new species apart, such as the fibrous ring reaching the abaxial hypodermis and the large first adaxial fibre bundle near the margin. The new species is assessed as critically endangered. Conclusion – Syagrus harenae is the first endemic species of the genus described for the Serra do Ambrósio and possesses striking characteristics, such as the re-greening of the pistillate flowers and flowers arranged in tetrads and pentads. The type population corroborates the Diamantina Plateau and its disjunctions as one of the centres of diversity for Syagrus . The discovery of this new species reinforces the uniqueness of the local flora and its classification as a priority area for conservation.