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Bacterial wilt of tomato is a destructive disease caused by <i>Ralstonia solanacearum</i> throughout the world. An endophytic actinomycete with antagonistic activity, designated strain LD120^T, was isolated from moss (<i>Physcomitrium sphaericum</i> (Ludw) Fuernr). The biocontrol test demonstrated that co-inoculation by the isolate and the pathogen gave the greatest biocontrol efficiency of 63.6%. Strain LD120^T had morphological characteristics and chemotaxonomic properties identical to those of members of the genus <i>Streptomyces</i>. The diamino acid present in the cell wall was LL-diaminopimelic acid. Arabinose, glucose, rhamnose, and ribose occured in whole cell hydrolysates. The menaquinones detected were MK-9(H₄), MK-9(H₆), MK-9(H₈), and MK-9(H₂). The polar lipid profile was found to contain diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylinositol. The major cellular fatty acids were found to be iso-C_16:0, iso-C_17:0, anteiso-C_15:0, and C_16:1 ω7c. The DNA G+C content of the draft genome sequence, consisting of 7.6 Mbp, was 73.1%. Analysis of the 16S rRNA gene sequence showed that strain LD120^T belongs to the genus <i>Streptomyces</i>, with the highest sequence similarity to <i>Streptomyces azureus</i> NRRL B-2655^T (98.97%), but phylogenetically clustered with <i>Streptomyces anandii</i> NRRL B-3590^T (98.62%). Multilocus sequence analysis based on five other house-keeping genes (<i>atpD</i>, <i>gyrB</i>, <i>rpoB</i>, <i>recA</i>, and <i>trpB)</i> and the low level of DNA–DNA relatedness, as well as phenotypic differences, allowed strain LD120^T to be differentiated from its closely related strains. Therefore, the strain was concluded to represent a novel species of the genus <i>Streptomyces</i>, for which the name <i>Streptomyces</i><i>physcomitrii</i> sp. nov. was proposed. The type strain was LD120^T (=CCTCC AA 2018049^T = DSM 110638^T).