About a month ago another blipper posted one of these saying it was new to him. I replied saying that I saw them almost every year on my photographic excursions.
This is the first one I have seen since then.
According to Wikipedia:
The rose bedeguar gall, Robin's pincushion gall, or moss gall develops as a chemically induced distortion of an unopened leaf axillary or terminal buds, mostly on wild rose shrubs, caused by the parthenogenetic hymenopteran gall wasp (Diplolepis rosae).