Senegalia comprises 219 species distributed in tropical and subtropical regions of North and South America, Africa, Asia and Australia. Two sections are currently recognised within Senegalia and these are most readily distinguished by the differences in disposition of their cauline prickles, i.e. sect. Senegalia with prickles at or near leaf nodes and sect. Monacanthea with mostly internodal prickles. Previous phylogenetic studies, based primarily on small numbers of plastid DNA loci, found Senegalia to be monophyletic with two large subclades corresponding to the sections. Here, we present new phylogenomic evidence from 997 single-copy nuclear gene sequences for a small, but representative set of species. These new analyses show that Senegalia is non-monophyletic, but instead, forms a grade that is paraphyletic with respect to the remainder of the ingoid clade (i.e. Ingeae + Acacia s.s. + Acaciella), comprising two well-supported subclades most likely representing the same clades as found in previous phylogenetic studies of the genus and, interspersed between these, a third, moderately supported clade, comprising the genera Mariosousa, Pseudosenegalia and Parasenegalia. In marked contrast to the nuclear phylogeny, the two Senegalia clades are sister groups in the plastid phylogeny, based on analyses of 72 chloroplast genes, rendering the genus monophyletic, based on plastid data alone. We discuss this new evidence that Senegalia is non-monophyletic in relation to the marked cytonuclear discordance, high gene tree conflict and lack of resolution across this senegalioid grade and review the consistency of the key morphological characters distinguishing the two sections of Senegalia. We conclude that it is likely that Senegalia will need to be split into two (or possibly more) genera: a re-circumscribed Senegalia s.s. that corresponds to the existing Senegalia sect. Senegalia plus the S. ataxacantha group (Senegalia sect. Monacanthea s.s.; future studies may show that this group warrants generic status) and a new genus corresponding to the remainder of sect. Monacanthea (here designated as Senegalia sect. Monacanthea p.p.). However, re-delimiting Senegalia now would be premature given that the key morphological characters are not fully congruent with the two sections and pending denser phylogenetic sampling of taxa. A judiciously selected list of critical taxa is presented to facilitate future phylogenomic studies. Finally, we discuss the identity of Albizia leonardii, which is also placed in this senegalioid grade in these new phylogenomic analyses and place it in synonymy with Parasenegalia vogeliana.

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Many tropical trees have high canopies and their leaves are not accessible. Thus, the use of tissue from a more accessible organ (cambium) for DNA extraction may be an alternative for molecular studies. We adapted a feasible methodology for extracting genomic DNA from cambium tissue harvested in the field for the assessment with PCR. We tested three storage conditions (two buffers and a silica gel) and four periods of time after harvest. We used previously described protocols and tested them on three species that occur in Amazonian forests and other biomes: Anadenanthera peregrina var. peregrina, Cedrela fissilis, and Ceiba speciosa. Our protocol obtained suitable PCR-grade genomic DNA for DNA sequencing and microsatellite genotyping. We recommend the use of silica for long-term storage and the buffer with ascorbic acid for short-term storage.

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Acacieae Benth. (Leguminosae-Mimosoideae) comprises more than 1450 species and is composed of five genera in the current circumscription: Senegalia Raf.,

The genus Piptadenia includes approximately 24 species that are distributed in the tropical regions of South America, with centers of diversity in the Amazon and Atlantic Forest in Brazil in which twenty-one species occur. A taxonomic study of Piptadenia was conducted in the state of Minas Gerais based on an analysis of approximately 270 specimens from 11 herbaria, field observations and field work in the main conservation units and other focal areas in Minas Gerais. These areas include the three vegetation domains in the state: Atlantic Forest, Cerrado and Caatinga. Six of the species in the genus were sampled: P. adiantoides, P. gonoacantha, P. macradenia, P. micracantha, P. paniculata and P. viridiflora. Two species that have previously been cited in the state were not found in this study: P. irwinii and P. stipulacea. These species were not found in the herbaria collections that were consulted or during the field work. We present an identification key for the Minas Gerais species of Piptadenia as well as descriptions, illustrations, geographical distributions, comments about the taxonomic characters and some information related to the flowering and fruiting periods.