Upper montane ecosystems in Brazil are little known, and their structural and functional aspects poorly understood. Our goals were to describe tree species diversity and community structure, and to characterize tree species in relation to their ecological traits, phytogeographic history and conservation status in an upper montane araucaria forest remnant. A total of 26 species belonging to 18 families were found in a 1-hectare permanent plot. The tree community mainly comprised trees with diameters of less than 20 cm and heights of between 6.5 and 9.5 m. Drimys angustifolia and Myrceugenia regnelliana had the highest importance values. Most species were shade tolerant while most individuals were pioneers. Most species and individuals presented zoophily and zoochory. Most sampled species and individuals were related to araucaria forests. Seven species are threatened to some degree while one species, Crinodendron brasiliensis, besides threatened, is also endemic to the region. The presence of endemic and endangered species demonstrates that the studied area serves important conservation purposes. Furthermore, the present study demonstrates the important role that upper montane regions have for conservation and describes the structural patterns of still poorly studied habitats, reinforcing the importance such systems have in maintaining species diversity at high elevations.

Phylogenetic studies indicate that several infrageneric taxa in Oxalis require taxonomic updates to attain monophyly. In this contribution, we update the morphological delimitation of the South American Oxalis sect. Ripariae and provide a taxonomic revision of the currently accepted species. The sectional delimitation was carried out by comparing micro- and macromorphological features of Oxalis sect. Ripariae, O. sect. Corniculatae, and O. sect. Myriophyllum. These sections share yellow flowers and aerial stems. Glandular hairs and larger seeds with the surface longitudinally crested and with projections are exclusive to Oxalis sect. Ripariae. We accept 11 species in the section, including three previously placed in Oxalis sect. Corniculatae (i.e., O. eriocarpa, O. niederleinii, and O. refracta), but excluding O. serpens and O. subvillosa, which are moved to O. sect. Corniculatae. We also describe a new species (Oxalis lourteiginana), propose a new name and status for O. bifrons subsp. littoralis (now O. pampeana), the synonymization of O. irreperta with O. riparia, six second-step lectotypifications, and one epitypification. For each accepted species we provide a morphological description, illustrations, ecological and taxonomic information, conservation status following IUCN, and a geographic distribution map. Most species occur in southern Brazil, but the section is widespread also in Argentina, Uruguay, and eastern Paraguay. Six species are categorized as threatened and further three as near threatened. Besides, we provide an identification key for the taxa of the section.