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The phylogenetic position and circumscription of the disjunct African genus Tribulocarpus is investigated with DNA sequences from plastid rps16 and trnL‐F, and nuclear ITS. Representatives from all four subfamilies of Aizoaceae are included in the analyses, most of them from Aizooideae and Sesuvioideae. The position of Tribulocarpus as sister to the rest of Sesuvioideae is confirmed, and we agree that the genus should be referred to this subfamily. Tetragonia retusa is found to be part of the Tribulocarpus clade with strong support. A new taxonomy of Tribulocarpus with two species is proposed and the new combination Tribulocarpus retusus is made. A lectotype is designated for Tetragonia somalensis. Tribulocarpus dimorphanthus, disjunctly distributed in south‐western and north‐eastern Africa, is retrieved as paraphyletic with regard to T. retusus, endemic in Somalia, as the latter is sister to the north‐east African part of T. dimorphanthus only. Despite the genetic difference between the samples from the disjunct populations of T. dimorphanthus no morphological differences could be detected. Tribulocarpus dimorphanthus–T. retusus is suggested as an example of a progenitor‐derivative species pair, where T. retusus has budded off from the north‐eastern partial area of distribution of T. dimorphanthus. The compound and spiny fruits of T. dimorphanthus versus the simple and broadly winged fruits of T. retusus indicate a rapid adaptive shift from zoochorous trample burrs to anemochorous nuts.

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A volcanic breccia (4 m thick) was recovered from middle Eocene sediments at Site 357, Leg 39, Rio Grande Rise, South Atlantic Ocean. The breccia is composed largely of basaltic fragments (~0.5 to 3 cm) and Eocene shallow-water fossils in a clayey matrix. Texture suggests a hyaloclastic origin, and sorting of components indicates slump deposition. Although most basaltic material is altered (smectities, carbonate), fresh clinopyroxenes (Fs*-i*Wθ45-ji) remain and have compositions similar to clinopyroxene in highly alkalic basaltic rocks, thus identifying the parentage of the altered basalt fragments. The affinity of both hyaloclastites and alkalic oceanic basaltic-material to seamounts and islands suggests that the breccia formed by eruption from an alkali-rich seamount or volcano, probably during Eocene time. Shallow-water fauna and sorting indicate that it subsequently slumped to a pelagic environment. This breccia provides the first quantitative data for the composition of basement material of the Rio Grande Rise, whereby it is composed, at least in part, of volcanic material not typically oceanic crust (tholeiitic).

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