Bacterial strain B29T1(T) was isolated from the endophytic microbial community of a Pinus pinaster tree trunk and characterized. Strain B29T1(T) stained Gram-negative and formed diplococci that grew optimally at 26-30 degrees C and at pH 6.0-7.0. The G+C content of the DNA was 61.6mol%. The respiratory quinone was ubiquinone 10 (UK-10), and the major fatty acids were C16:0, cyclo-C19:0omega8c and C18:0 12-methyl, representing 64% of the total fatty acids. Phylogenetic analyses based on the 16S rRNA gene sequences placed strain B29T1(T) within the order Rhodospirillales in a distinct lineage that also included the genus Geminicoccus. The 16S rRNA gene sequence similarities of B29T1(T) to that of Candidatus Alysiomicrobium bavaricum, Geminicoccus roseus and Candidatus Alysiosphaera europeae were 92.6%, 89.9% and 89.2%, respectively. The analysis of the available genomes from the closest families showed 177 core genes that reveals a novel family-level clade including the type strain of the genus Geminicoccus and the strain B29T1(T). Analysis of B29T1(T) genome revealed all the genes involved in autotrophic carbon dioxide fixation via the reductive pentose phosphate pathway and genes encoding for starch/glycogen and chitin degradation. The phylogenetic, phenotypic and chemotaxonomic data showed that strain B29T1(T) (=CIP 110763(T), =LMG 27745(T)) represents the type of a novel species and genus, for which we propose the name Arboriscoccus pini gen. nov., sp. nov. A new family (Geminicoccaceae fam. nov.) is proposed for Arboriscoccus, Geminicoccus, Candidatus Alysiomicrobium and Candidatus Alysiosphaera. The description of the Geminicoccus roseus DSM 18922(T) is also emended.