Flowers are pentamerous with (usually) five stamen, a five-lobed calyx tube and a five-petalled corolla, the latter bright yellow and an wide. The flowers are almost sessile, with very short pedicels (2 mm, 0.08 in). The five stamens are of two types, with the three upper stamens being shorter, their filaments covered by yellow or whitish hairs, and having smaller anthers, while the lower two stamens have glabrous filaments and larger anthers. The plant produces small, ovoid (6 mm, 0.24 in) capsules that split open by way of two valves, each capsule containing large numbers of minute, brown seeds less than 1 mm (0.04 in) in size, marked with longitudinal ridges. A white-flowered form, "V. thapsus" f. "candicans", is known to occur. Flowering lasts up to three months from early to late summer (June to August in northern Europe), with flowering starting at the bottom of the spike and progressing irregularly upward; each flower opens for part of a day and only a few open at the same time around the stem.