A Gram-reaction-positive, non-motile actinobacterium, designated strain 210121(T), was isolated from rhizosphere soil of the mangrove fern Acrostichum speciosum. 16S rRNA gene sequence analysis showed that the isolate belonged to the genus Asanoa. DNA-DNA relatedness values between strain 210121(T) and the type strains of the three recognized species of the genus Asanoa were below the 70 % threshold recommended for distinguishing bacterial genomic species. The novel isolate contained glutamic acid, glycine, alanine and meso-A(2)pm as cell-wall amino acids, indicating peptidoglycan type A1γ. The characteristic whole-cell sugars were xylose, ribose, glucose and mannose. The predominant menaquinones were MK-9(H(4)), MK-9(H(6)) and MK-9(H(8)). The major fatty acids were iso-C(16 : 0) (30.9 %), C(17 : 0) (23.0 %), anteiso-C(15 : 0) (14.9 %) and iso-C(15 : 0) (12.3 %). The phospholipid profile comprised phosphatidylethanolamine, phosphatidylinositol mannosides and phospholipids of unknown structure containing glucosamine. The G+C content of the DNA was 70.3 mol%. On the basis of the phenotypic and genotypic data, strain 210121(T) ( = CGMCC 4.5593(T) = DSM 45427(T)) represents a novel species of the genus Asanoa, for which the name Asanoa hainanensis sp. nov., is proposed. An emended description of the genus Asanoa is also proposed.