Arcytophyllum leymebambense (Rubiaceae: Spermacoceae), a new species with an isolated phylogenetic position and distinct morphology from northern Peru

Background and aims – The newly described species Arcytophyllum leymebambense sp. nov. (Rubiaceae) from the Amazonas department of northern Peru represents an isolated lineage within the monophyletic genus Arcytophyllum. This study aims to describe its distinctive morphological features and ecological context, assess its phylogenetic position, and discuss its implications for the diversification of the genus in the Andes. Material and methods – Morphological observations were conducted on herbarium specimens and field collections from the type locality. Phylogenetic analyses were performed using nuclear and plastid DNA sequences from the tribe Spermacoceae, with particular emphasis on Arcytophyllum. Key results – Arcytophyllum leymebambense sp. nov. is morphologically distinct from its congeners by its acuminate leaf and sepal apices, hirsute-lanuginose seeds, and the presence of protective hooks surrounding the ovary. It inhabits humid, high-elevation grasslands known as “Jalca,” where it coexists with a diverse assemblage of montane species. The species appears to be endemic to the region and is currently known from only three populations. Its restricted distribution, combined with potential threats such as overgrazing and fire, supports a preliminary conservation assessment as Critically Endangered (CR). Conclusion – The discovery of Arcytophyllum leymebambense sp. nov. highlights the underestimated diversity of Andean Rubiaceae and provides evidence that Andean species form a grade within the diversification of Arcytophyllum. This pattern suggests a historical northward expansion of the lineage into the high mountains of Panama and Costa Rica.