Uncovering hidden diversity: Oldenlandia bahiana, a neglected new species endemic to Brazil (Spermacoceae, Rubiaceae), revealed by integrative approach

Background and aims – Oldenlandia is a taxonomically complex and polyphyletic genus with approximately 160 pantropical species distributed across more than ten clades. In an ongoing integrative review of South American representatives, distinct morphological and ecological variation was detected among specimens previously assigned to O. filicaulis. This prompted the recognition and description of a new species, which is circumscribed here based on multiple lines of evidence.

Material and methods – Eighty herbarium specimens were analysed. Classical taxonomic techniques were employed, including type revision, and different databases were consulted. A principal component analysis based on 19 climatic and nine edaphic variables was conducted, together with the comparative analysis of micromorphological floral, carpological, and pollen characteristics was performed using optical and scanning electron microscopy.

Line drawings, geographical records mapping, and a preliminary conservation assessment were also carried out. Key results – The analysed specimens have a set of unique characteristics when compared with O. filicaulis, such as floral merosity, variation in the shape and size of calyx and corolla lobes, type and distribution of corolla indumentum, presence of a pubescent style (vs glabrous), number of pollen apertures, and variation in sexine ornamentation.

Distribution patterns also differ: O. filicaulis occurs in Bahia, Ceará, and Piauí, whereas the differentiated specimens are recorded exclusively in the high-altitude rupestrian grasslands in Bahia. Conclusion – The combined evidence supports the recognition of a new species. Further molecular phylogenetic studies are needed to clarify its placement within Spermacoceae and its relationships to other species of the genus, especially the South American taxa.

This new species discovery reinforces the extraordinary diversity and endemism of the Brazilian rupestrian grasslands. An identification key for all Oldenlandia species occurring in Brazil is provided.