Purple Salsify or Oyster Plant. (the root supposedly tastes like oysters)
A European invader.
In May it produces huge dandelion-like seed heads, about 4 inches in diameter (10cm). These seed heads are the most obvious feature as the blooms don’t seem to last long — one bloom I watched was beginning to open at 6:30am and was closed up by 2pm the same day, nor did it reopen the next day at 6:30.
I first noticed a seed-head at the end of April and first noticed a flower at the end of May, which is backwards of course. I believe it blooms between April and September.