Two novel Gram-stain positive actinobacteria, designated PS-14-16(T) and RS-7-1, were isolated from the rhizosphere of a mangrove and sea sediment, respectively, and their taxonomic positions were investigated by a polyphasic approach. Both strains were observed to form vegetative hyphae in the early phase of growth but the hyphae eventually fragment into short rods to coccoid cells. The peptidoglycan type of both strains was found to be A4α. Their predominant menaquinone was identified as MK-9(H4) and the major fatty acid as anteiso-C(15:0). The DNA G+C content was determined to be 68.4-68.5 mol%. 16S rRNA gene sequencing revealed that strains PS-14-16(T) and RS-7-1 were related to members of the family Cellulomonadaceae. Their nearest phylogenetic neighbour was found to be Sediminihabitans luteus, which is currently the only species of the genus Sediminihabitans, with a similarity of 97.94%. However, strains PS-14-16(T) and RS-7-1 were distinguishable from the members of the genus Sediminihabitans and the other genera within the family Cellulomonadaceae in terms of chemotaxonomic characteristics and phylogenetic relationship. The results of DNA-DNA hybridization experiments indicated that strains PS-14-16(T) and RS-7-1 belong to the same species. Strains PS-14-16(T) and RS-7-1 are concluded to represent a novel genus and species of the family Cellulomonadaceae, for which the name Tropicihabitans flavus gen. nov., sp. nov. is proposed. The type strain of T. flavus is PS-14-16(T) (=NBRC 110109(T) = IanCC A 516(T)). [corrected].