From Little Acorns...
... it is unlikely a mighty oak will grow!
This cluster of acorns is blighted by Knopper Galls, caused by Cynipid gall wasp (Andricus quercuscalicis) which lays eggs within the tree buds. In response tree increases it's production of its growth hormones. This makes the growth and development of the nut, or acorn, go a bit haywire, resulting in wavy, knobby formations. They don't effect the overall health of the tree forntunately, but there'll be no new trees from these acorns.
For TinyTuesday hosted by KangaZu.