erm, far be it to for me to disagree with the above fine sugestions but i think it may be a thing plants sometimes get called "Proliferation" or "Fasciation"...
Proliferation occures when a flower or leaf bud gets slightly damaged, usually from a nibbly insect. As the plant tries to repair the damage it sort ov goes into overdrive and starts to build a wierd shaped protuberance...This is sometimes seen on Wild Roses and Antihrinums.
Alternatively it may be a thing called Fasciation which occures when a flower or leaf bud gets damaged, usually by some sort ov Herbicide such as Glyphosate. This causes a Genetic Change in the Flower or Leaf Bud's cells and is often seen on Raspberries that have encountered "Spray-drift" when something nearby has been treated and a tiny amount has landed on the plant.
I think its more likely to be the first one as the damage must have been really small, and weed-killer damage would be bigger, unless a tincy-wincy-tiny bit got on...
Is the protuberance hard like Wax or Hollow like a blade ov grass?
Seana (The Gardener)
XXX