No interactions present.
If we assume that it is a species of speedwell present in Britain then Veronica serpyllifolium seems to be the best match for leaf shape and inflorescence structure (scale permitting). But the location is given as at altitude in southern Bulgaria, so there could be other species to throw into the mix.
I hadn't spotted where it had been found,and had just assumed it was British. I must look more carefully in future.
Lat/Lng: 41.6, 25.3