Myrcia is the second-largest genus of Myrtaceae, comprising over 770 recognized species. In Costa Rica, 16 species have been recorded, of which six are endemic. In this study, we describe and illustrate a new species, Myrcia osaensis, found in the lowland forests of the southern Pacific region of Costa Rica. This new species exhibits distinct characteristics, including large leaves with suppressed secondary venation; underside of leaves, inflorescences, and flower buds bearing T-shaped trichomes; pyramid-shaped panicles; flower buds with obtuse to very shortly rostrate calyptra and globose fruits. We include photographic documentation of the new species, a comparative table and a composition summarizing key characters to distinguish M. osaensis from its most morphologically similar species, M. lonchophylla and M. longicalyptrata. The new species is preliminarily assessed as least concern (LC) based on the IUCN criteria. This discovery increases the number of Myrcia species known from Costa Rica to 17, of which seven are endemic, highlighting the importance of continued floristic exploration, study and documentation of the genus.
