Plant 307

Dipsacus fullonum L. (Caprifoliaceae)

Wild teasel

Silhouettes of teasels are a common sight in fields and gardens in the UK, often accompanied in autumn by goldfinches feeding on the spiky, ovoid seed-heads. Native to Britain, they set seeds readily and are often found uninvited in gardens, although they may also be planted intentionally by gardeners who appreciate their striking architectural shape and value to wildlife.

Dipsacus fullonum is the most familiar species, growing up to two metres tall. It is a biennial plant, forming a rosette of leaves in the first year, followed by a flowering stalk in the second, topped by the familiar hedgehog-like flowerheads. The pale purple flowers open sequentially in two separate narrow rings, giving the appearance that the flowers are moving up and down the inflorescence. The stems, and to a lesser extent the leaves, are spiny.

The oppositely paired, sessile leaves have bases which clasp the stem, forming a cup which collects rainwater. This often contains drowned insects, leading to speculation that this leaf structure provides a defence against herbivorous insects which attempt to climb the stem. It has also been suggested that teasels practise a form of carnivory, as the nutrients from the insects are eventually absorbed by the plant. This feature inspired another common name, Venus's basin, and the generic name Dipsacus, which derives from the Greek word dipsa, meaning thirst.

Another British native species, Dipsacus pilosus, the small teasel, is shorter than wild teasel, with more rounded flower-heads and white flowers. The genus contains about 20 species, whose native range extends across Europe, Asia and North Africa. Dipsacus fullonum has spread outside its natural range and in some places, especially the USA, has become invasive.

Teasel seed-heads have long been used in the textile industry, both for the carding of unspun fibres, and for finishing woollen cloth. This is acknowledged in the specific epithet fullonum, indicating its use by fullers. The seed-heads were originally mounted onto handles which were used to brush the cloth to create a soft pile, or nap, on the surface. Later they were incorporated into more efficient rotary machines for the same purpose.

During the twentieth century they were superseded by metal combs, which last longer and are more uniform, but are also more rigid, and prone to tear the cloth. The flexible spines of teasel heads are less likely to damage the cloth, making them an example of nature's engineering surpassing human design.

Further reading

Naghiloo S and Classen-Bockhoff R 2017. Understanding the unique flowering sequence in Dipsacus fullonum: evidence from geometrical changes during head development. PLoS ONE 12: e0174091.

Shaw PJA and Shackleton K 2011. Carnivory in the teasel Dipsacus fullonum - the effect of experimental feeding on growth and seed set. PLoS ONE 6: e17935.

Werner PA 1975. The biology of Canadian weeds: 12. Dipsacus sylvestris Huds. Canadian Journal of Plant Science 55: 783-794.

Ruth Calder