Target leaf-spot fungus on clover

Some of the leaves of the white clover (Trifolium pratense) has developed target leaf-spot fungi, probably, I think, Stemphylium sarciniforme (there are many leaf spotting fungi found on clovers and they all look very similar unless studied under a high power microscope).

They are called 'target fungi' because they tend to make target-like concentric rings on the leaf.