Great mullein

Appearance

''V. thapsus'' is a dicotyledonous plant that produces a rosette of leaves in its first year of growth. The leaves are large, up to 50 cm long. The second-year plants normally produce a single unbranched stem, usually 1–2 m tall. In the eastern part of its range in China, it is, however, only reported to grow up to 1.5 m tall.

The tall, pole-like stems end in a dense spike of flowers that can occupy up to half the stem length. All parts of the plants are covered with star-shaped trichomes. This cover is particularly thick on the leaves, giving them a silvery appearance. The species' chromosome number is 2n = 36.

On flowering plants, the leaves are alternately arranged up the stem. They are thick and decurrent, with much variation in leaf shape between the upper and lower leaves on the stem, ranging from oblong to oblanceolate, and reaching sizes up to 50 cm long and 14 cm across.

They become smaller higher up the stem, and less strongly decurrent down the stem. The flowering stem is solid and 2–2.5 cm across, and occasionally branched just below the inflorescence, usually following damage. After flowering and seed release, the stem and fruits usually persist in winter, drying into dark brown, stiff structures of densely packed, ovoid-shaped, and dry seed capsules. The dried stems may persist into the following spring or even the next summer. The plant produces a shallow taproot.

Flowers are pentamerous with five stamen, a five-lobed calyx tube and a five-petalled corolla, the latter bright yellow and an 1.5–3 cm wide. The flowers are almost sessile, with very short pedicels. 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 capsules that split open by way of two valves, each capsule containing large numbers of minute, brown seeds less than 1 mm 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 , 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.

Distribution

''Verbascum thapsus'' has a wide native range including Europe, northern Africa and Asia, from the Azores and Canary Islands east to western China, north to the British Isles, Scandinavia and Siberia, and south to the Himalayas. In northern Europe, it grows from sea level up to 1,850 m altitude, while in China it grows at 1,400–3,200 m altitude.

It has been introduced throughout the temperate world, and is established as a weed in Australia, New Zealand, tropical Asia, La Réunion, North America, Hawaii, Chile, Hispaniola and Argentina. It has also been reported in Japan.

In the United States it was imported very early in the 18th century and cultivated for its medicinal and piscicide properties. By 1818, it had begun spreading so much that Amos Eaton thought it was a native plant. In 1839 it was already reported in Michigan and in 1876, in California. It is now found commonly in all the states. In Canada, it is most common in the Maritime Provinces as well as southern Quebec, Ontario and British Columbia, with scattered populations in between.

Habitat

Great mullein most frequently grows as a colonist of bare and disturbed soil, usually on sandy or chalky ones. It grows best in dry, sandy or gravelly soils, although it can grow in a variety of habitats, including banksides, meadows, roadsides, forest clearings and pastures. This ability to grow in a wide range of habitats has been linked to strong phenotype variation rather than adaptation capacities.

Evolution

Seed of Verbascum thapsus has been recorded from part of the Cromer Forest Bead series and at West Wittering in Sussex from some parts of the Ipswichian interglacial layers.