Flower:

Branching clusters of stalked flowers at the tips of branching stems and arising from upper leaf axils. Flowers are about ¾ inch across and about 1 inch long, with 5 spreading white petals each deeply divided into 2 rounded lobes. Long white stamens with dark tips and 3 pale styles extend out of the throat. The calyx is light green to pinkish, smooth with distinct venation, has 5 small triangular lobes at the tip, and is typically inflated like a balloon, oval to nearly round.

Leaves and stems:

Leaves are ¾ to 3 inches long, up to 1¼ inch wide, narrowly lance-oblong or may be widest above the middle, toothless, hairless to sparsely hairy, pointed at the tip, rounded at the base, stalkless and nearly clasping. Stems are branched near the base, light green and smooth with a waxy bloom.

Fruit:

Fruit is a teardrop shaped capsule about as long as the calyx. When ripe it splits open at the top, the 6 teeth flaring out. Inside are round to kidney-shaped seeds, black or nearly so.

Notes:

Bladder Campion is a less common weed than the similar Balkan Catchfly (Silene csereii), which also has a smooth calyx but has proportionately broader, more egg-shaped leaves, a less inflated calyx with obscure venation, is more erect and not typically branched except in the flower clusters. There are 5 subspecies of Silene vulgaris in its native Europe but apparently subsp. vulgaris is the primary species in North America.