Strain EuI1cT is the first actinobacterial endophyte isolated from Elaeagnus umbellata that was shown to be infective on members of Elaeagnaceae and Morella but lacking the ability to form effective root nodules on its hosts. The strain can be easily distinguished from strains of other Frankia species based on its inability to produce vesicles, the specialized thick-walled structures where nitrogen fixation occurs. Chemotaxonomically, strain EuI1cT contains phosphatidylinositol, diphosphatidylglycerol, two glycophospholipids and phosphatidylglycerol as phospholipids. The whole cell sugars were composed of glucose, galactose, mannose, ribose, rhamnose and fucose as diagnostic sugars of the species. Major fatty acids were iso-C16:0, C17:1 ω8c and C15:0 and C17:0 and the predominant menaquinones were MK-9(H6), MK-9(H8) and MK-9(H4). Analysis of the 16S rRNA gene sequence of strain EuI1cT showed 97, 97.4 and 97.9% identity with Frankia elaeagni DSM 46783T, Frankia casuarinae DSM 45818T and Frankia alni DSM 45986T, respectively. Digital DNA:DNA hybridizations with type strains of the three Frankia species with validly/effectively published names are significantly below 70%. These results warrant distinction of EuI1cT (= DSM 45817T = CECT 9037T) as the type strain of a novel species designated Frankia inefficax sp. nov.