ABSTRACT During fieldwork in the Campos Amazônicos National Park, Amazonas state, Brazil, a new endemic species of Mabea was collected in savanna areas. Field collections and specimens in RON, MG, and HRCB were analyzed. To understand the species distribution and verify possible areas of occurrence, niche modeling was conducted using the sdm package in R. Mabea dalyana, the new species is a subshrub with xylopodia and reduced size (less than 1 m height) and small, yellow thyrses. There are several allopatric species of Mabea growing in Amazonian savannas, some widespread but others locally restricted, such as M. uleana from central Amazonia that has some superficial resemblance in leaves and inflorescences but can be distinguished from M. dalyana by pubescent adaxial leaf surface (vs. glabrous), 12-21 submarginal glands (vs. 10 submarginal glands), thyrse brownish to red (vs. yellow thyrse) and conspicuous caruncle (vs. caruncle inconspicuous). M. dalyana is endemic to hyperseasonal savanna, very well adapted to savanna, and fire tolerant. It has notable characteristics, such as a subshrub habit, a xylopodium, glabrous leaves, and sepals noticeably larger than the ovary.

A tribo Hippomaneae é discutida em relação à sua história taxonômica, posição sistemática nas Euphorbiaceae, em seus principais caracteres morfológicos diagnósticos, com ênfase no botão floral, em sua atual filogenia e subdivisão, e em seus padrões gerais de diversidade. A tribo está representada no Brasil por 13 gêneros e cerca de 120 espécies. Uma chave para os gêneros brasileiros é fornecida. Todos os gêneros do Brasil são discutidos sucintamente, citando-se suas características mais relevantes, a literatura taxonômica mais recente e o seu estado atual de conhecimento, bem como algumas sugestões para problemas ainda não resolvidos sobre os táxons. Há revisões publicadas para cinco dos gêneros, sendo que seis já foram revisados ou estão sendo revisados, mas permanecem inéditos. Actinostemon e Gymnanthes são atualmente os gêneros mais difíceis, especialmente pela ausência de referências taxonômicas atuais disponíveis. Para Mabea e Senefeldera, gêneros já revisados, mas não publicados, são fornecidos dados adicionais sobre a taxonomia, ecologia e biogeografia.

The tribe Hippomaneae (Euphorbiaceae) in Brazil. The tribe Hippomaneae is discussed with respect to its taxonomic history, its placement within the Euphorbiaceae, its diagnostic characters (particularly the floral buds), current data on phylogeny and subdivision, and its general pattern of diversity. The tribe is represented in Brazil with 13 genera and ca. 120 species. A key to the Brazilian genera is provided. All Brazilian genera are discussed, citing relevant characters, recent taxonomic literature, and the current state of knowledge, sometimes pointing to unresolved problems. For five of the genera, published revisions exist; six genera have unpublished but completed revisions or are currently under revision. Actinostemon and Gymnanthes are currently the most difficult genera, mostly based on the absence of available up-to-date taxonomic references. For Mabea and Senefeldera, two genera with completed but currently unpublished revisions, additional data are given on aspects of their taxonomy, ecology and biogeography.