A novel endophytic actinobacterium, designated strain EUM 378(T), was isolated from the surface-sterilized root tissue of Eucalyptus microcarpa, a eucalyptus tree known as Grey Box. Phylogenetic evaluation based on 16S rRNA gene sequence analysis, including alignment with taxon-specific 16S rRNA gene signature nucleotides, placed this isolate as a member of the family Nocardioidaceae. Strain EUM 378(T) showed >5.5 % 16S rRNA gene sequence divergence from other members of this family and was related most closely to Actinopolymorpha alba YIM 48868(T) (94.2 %) and Actinopolymorpha singaporensis IM 7744(T) (94.4 %). This Gram-positive, aerobic actinobacterium has well-developed substrate mycelia that fragment into small rods. Chemotaxonomic data revealed that the cell wall contains LL-diaminopimelic acid, ribose, glucose and rhamnose. MK-10(H₆) is the predominant menaquinone. Chemotaxonomic and phylogenetic evidence confirmed that strain EUM 378(T) represents a novel species of a new genus, for which the name Flindersiella endophytica gen. nov., sp. nov. is proposed. The type strain is EUM 378(T) ( = DSM 45355(T) = ACM 5289(T)).