Verbascum thapsus, commonly known as great mullein, is a biennial herbaceous plant of the Scrophulariaceae family that can reach up to two metres in height. During its first year it develops a basal rosette of large, oval leaves covered in a dense, soft down that gives them a characteristic greyish, velvety appearance. In its second year the plant produces a tall, erect flowering stem bearing a compact spike of bright yellow flowers. Flowering occurs in summer, generally between June and August, with the corollas opening only a few at a time over several weeks.

Native to Europe, North Africa and Asia, this plant thrives in dry, sunny and well-drained soils, colonising roadsides and slopes and has become widespread in temperate regions around the world, being able to grow and well adapt in the Mediterranean area.

The flowers and leaves are the parts richest in active compounds, and each has its own harvest window. The leaves can be gathered between the end of the first year and the beginning of the second, ideally in late spring or early summer, when the plant is still in its rosette stage, while the flowers are collected only from the second year, at full bloom.