Greater Birdsfoot Trefoil is Common Birdsfoot Trefoil plus….. Here is a photo of Greater Birds foot trefoil.
And here is Common Birdsfoot Trefoil…. see what I mean.
The main difference is that Greater Birdsfoot Trefoil has more flowers per head, between 5 to 12 also they are pure yellow whereas Birdsfoot trefoil only has 3 to 6 flowers and they can show some orange colour thus the common name eggs and bacon.
The ‘birdsfoot’ name comes from the arrangement of the seed pods which splay out like a birds foot and as the Common Birds foot trefoil typically has four or five flowers it will produce that many pods and thus look like the five toes of a birds foot. Greater Birdsfoot trefoil will look less like a birds foot as not many birds have 10 or 12 toes! The trefoil is because the leaves are composed of three leaflets.
Other minor differences are that Greater Birdsfoot Trefoil has hollow stems and the leaves are a bit richer green. Also it grows in damp and sometimes shady woodland habitats, whereas Common Birdsfoot Trefoil is more a plant of dryer and open habitats.
They are of course members of the Leguminosae or Pea family and as such will have root nodules which can fix nitrogen and thus live in areas where the supply of nitrates is less than adequate for other species. I often came across Common Birdsfoot Trefoil on sand dunes… not renowned for their fertility.