Also known as Korean bellflower, Chinese bellflower, Japanese bellflower, and common balloon flower.
The balloon flower is an herbaceous perennial with dark green leaves and blue flowers in late summer. A notable feature of the plant is the flower bud which swells like a balloon before fully opening. The five petals are fused together into a bell shape at the base. (Thanks to Wikipedia.)
The Garden Guides website has more complete information about the plant. Here is a sample…
The upward-facing flowers bloom throughout the summer and into early fall in shades of blue, pink and white. The plants form a low, neat mound and bear 2- to 3-inch cuplike blossoms accented with delicate purple veins and yellow stamens. Balloon flowers are a cottage garden standard, and they are excellent for cutting. To make the flowers last in the vase, sear the stems with a match or candle flame immediately after cutting.
Here is a photo of the bud in its “balloon” state:
I did not capture the photo of the buds (above). That photo is courtesy of the WikiNut website.