A well resolved triplet minus singlet spectrum of the primary donor P870 of the green bacterium Chloroflexus au- rantiacus, detected by optically detected magnetic resonance (ODMR), in intact membranes, was reported in our previous work [Photosynth. Res. 71 (2002) 45]. The spectrum is now interpreted and reconstructed by calculating the electronic interactions between the primary donor and the BChl a molecules belonging to the 866 absorption com- ponent of the B808-866 light-harvesting complex. The good agreement between the calculation and the experimental data strongly supports a topological model for the B808-866 complex which consists in a circular aggregate structure of a number of polypeptide units binding BChl a molecules assembled as in the LH2 peripheral antenna complex of purple bacteria, giving rise to two spectral forms. The aggregate surrounds the reaction centre (RC) resembling in this respect the LH1 core antenna complex of purple bacteria.