Tropical America (the Neotropics) harbours more plant species than any other region on Earth. The contribution of rare species to this diversity has been recently recognised, but their spatial distribution remains poorly understood. Here, we use all collection records of angiosperms from the Global Biodiversity Information Facility to delineate Neotropical bioregions, and to identify putatively rare species within the Neotropics and the Amazonian rainforest. We analyse the spatial distribution of these species and validate the results on a largely independent dataset based on vegetation plots from the Amazon Tree Diversity Network. We find that rare species are homogeneously distributed through most parts of the lowland Neotropics and Amazonia, but more concentrated in highlands. The second collection of any rare species is most often found in the close vicinity of the first, but in 20% of cases they are more than 580 km apart. We also find cross-taxonomic patterns of disjunct distributions within the Andes, the Atlantic forest in eastern Brazil, and between Amazonia and the Atlantic forest, but no clear disjunction patterns within lowland areas. These results suggest that a considerable proportion of rare plant species have surprisingly large distribution ranges, and that collections of rare species across most of the lowland Neotropics, and in particular in Amazonia, show no clear directionality. The second record of many rare species may be found virtually anywhere, urging the need for intensifying and broadening biological sampling.

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O Cariri Paraibano, situado numa depressão do Planalto da Borborema na Paraíba, é considerado uma das áreas prioritárias para a conservação da Caatinga. O presente trabalho teve como objetivo realizar o levantamento e caracterização das espécies de Rubiaceae presentes no Cariri Paraibano, visando contribuir com a taxonomia da família e com os estudos florísticos na região. Foram identificados 15 gêneros (Borreria, Chiococca, Cordiera, Coutarea, Diodella, Guettarda, Leptoscella, Manettia, Mitracarpus, Oldenlandia, Randia, Richardia, Spermacoce, Staelia e Tocoyena,) e 21 espécies de Rubiaceae na área. Apresenta-se uma chave para identificação das espécies bem como descrições, ilustrações e comentários sobre as espécies estudadas.

Chiococca and Salzmannia are similar and related, but have not been well studied. A review of their morphology clarified their separation and found that some variation documented in Chiococca has been overlooked, and the corolla lobes of Salzmannia are narrowly imbricated, not valvate in bud, and its flowers are protandrous and homostylous, with the style markedly elongated after anthesis. Chiococca is represented in northeastern Brazil by four species, and their distinctions are clarified. The problematic species Erithalis insularis, of Fernando de Noronha Island, better agrees morphologically and biogeographically with Chiococca, and is here transferred to this genus with the new combination Chiococca insularis; Erithalis is therefore restricted to the Caribbean basin. Salzmannia is endemic to coastal eastern and northeastern Brazil, and comprises two species; S. arborea, described here, is found along the coast of Bahia and notable in its tree habit and dimorphic vegetative and reproductive stems.

This paper presents the first record of Chomelia triflora from Brazil, to date a species only known from French Guiana. After examining herbaria collections and doing fieldwork in the Brazilian Amazon, we found that the species also occurs in and around the Ducke Reserve in the state of Amazonas, Brazil. Our finding increases the data about the Brazilian Amazon and contributes to the better knowledge of Chomelia in Brazil.