Burkholderia endophytes were identified within the leaves of non-nodulated members of the genus Psychotria. In contrast to leaf-nodulated Psychotria species, which are known to accommodate their endosymbionts into specialized endosymbiont-housing structures, non-nodulated species lack bacterial leaf nodules and harbor endosymbionts intercellularly between mesophyll cells. Based on molecular data (rps16, trnG, and trnLF), the phylogenetic reconstruction of the host plants revealed a separate origin of leaf-nodulated and non-nodulated Psychotria species. Despite a distinct phylogenetic position of the two host clades, the endophytes of the non-nodulated plants were not placed into a single monophyletic group but were found to be closely related to the leaf-nodulated endosymbionts. The observation of genetically similar endophytes in both nodulated and non-nodulated Psychotria lineages suggests that the host plant is playing a crucial role in the induction of leaf nodule formation. Moreover, the concentration of endosymbionts into specialized leaf nodules may be considered as a more derived evolutionary adaptation of the host plant, serving as an interface structure to facilitate metabolic exchange between plant and endosymbiont.

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The littoral forests of the Libreville area (Gabon) and their importance for conservation: description of a new endemic Psychotria species (Rubiaceae)Background -A new species of Rubiaceae, Psychotria wieringae O.Lachenaud, is described and illustrated. Methods -Normal practises of herbarium taxonomy have been applied. Key results -P. wieringae is endemic to the Libreville peninsula (Gabon), where it is locally abundant in the undergrowth of littoral forests on sandy soils. It is related to P. gabonica Hiern but differs in its pale bark, glabrous inflorescences, flower colour, and leaves with a prominent midrib on the upper surface. IUCN assessment -The species is considered as Endangered EN B2ab(i,ii,iii,iv,v) according to IUCN criteria. Its survival in situ will likely depend on the maintenance of the subpopulation at the "Ferme des crocodiles", situated in the Raponda-Walker Arboretum. The occurence of several other endemic species in the area, and their conservation, are also discussed.Contexte -Une nouvelle espèce de Rubiaceae, Psychotria wieringae O.Lachenaud, est décrite et illustrée. Méthodes -Les méthodes usuelles de taxonomie d'herbier ont été appliquées. Résultats-clés -P. wieringae est endémique de la péninsule de Libreville (Gabon) où il est localement abondant dans le sous-bois des forêts littorales sur sol sableux. Voisin de P. gabonica Hiern, il en diffère notamment par son écorce claire, les inflorescences glabres et la couleur des fleurs, et par la nervure médiane des feuilles saillante à la face supérieure. Estimation UICN -L'espèce est considérée comme En danger EN B2ab(i,ii,iii,iv,v) selon les critères de l'UICN. Sa survie en condition in situ dépendra probablement du maintien de la sous-population de la "Ferme des crocodiles", située dans l'Arboretum Raponda-Walker. La présence de plusieurs autres espèces endémiques dans la région, et leur conservation, sont également discutées.

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