Paulownia tomentosa Steud. (Paulowniaceae)


Princess tree

Paulownia tomentosa inflorescence. Paulownia tomentosa in Oxford Botanic Garden. Paulownia tomentosaI from Curtis?s Botanical Magazine (1852; t.4666)

Paulownia tomentosa is a beautiful, deciduous tree, which can be an invasive weed in some parts of the world. It has attractive foxglove-like flowers, hence another of its common names - the foxglove tree. Traditionally, the genus Paulownia was part of the foxglove family, Scrophulariaceae, but in the last 15 years, this family has been split-up based on DNA evidence. In May, before the leaves emerge, the delicately scented, purple flowers form on the mature growth and, on a sunny day, look stunning against a blue, spring sky.

The mature foliage is heart-shaped, and each leaf is around 15 cm across. However, immature plants have huge leaves, at least dinner plate-sized, to catch every ray of sunshine that reaches them. The immature foliage is tropical in appearance, and can be maintained in older plants by coppicing - cutting down the plant to ground level at the end of the growing season. The new spring growth will have luscious, glossy green leaves; perfect at the back of a sub-tropical border.

Paulownia is a very fast-growing tree in its native China, and other areas with similar climates. It can grow to 15 m at full maturity, and annual growth rings have been recorded up to 8 cm apart! Its rapid maturation leads to the old Chinese custom of planting Paulownia seed at the birth of a baby girl. As the child grows so does the tree, and when she is married, the Paulownia is felled and the furniture and ornaments made from the wood become part of her dowry. Working Paulownia wood has become a skilled craft in China and Japan.

Paulownia is quick to mature, but as a consequence is a relatively short-lived tree. Its roots, having developed quickly, are often weak, and the mature trees often become unstable.

Paulownia produces an abundance of small, fluffy, wind-dispersed seed inside an egg-shaped capsule. The lightweight texture of the seed made it an excellent packing material for the export of porcelain from China in the nineteenth century. The porcelain would be transported by rail in wooden crates. The ease with which the wooden crates would crack, and the seed dispersed, led to Paulownia trees being a common sight along railway lines in China and latterly in the eastern United States. Today, in the United States, Paulownia is classed as an invasive weed, and in the state of Connecticut it is illegal to sell Paulownia trees.

Further reading

Ding J et al. 2006. Biological control of invasive plants through collaboration between China and the United States of America: a perspective. Biological Invasions 8, 1439-1450.

Essl F 2007. From ornamental to detrimental? The incipient invasion of Central Europe by Paulownia tomentosa. Preslia 79, 377-389.

Tree of the World 2014. Paulownia tomentosa. Royal Botanic Garden.

Ali Quantrell

BBC Radio Oxford clip about this week's plant