Ptelea trifoliata L. (Rutaceae)


Hop tree

Coloured engraving of the hop tree from Mark Catesby's 'Natural History of Carolina, Florida and the Bahama Islands' (1754, t.83). Specimen of hop tree collected in South Carolina, USA, in 1723 by Mark Catesby (Oxford University Herbaria).

The eighteenth century was an exciting time to be a wealthy European with an interest in plants. Plant collectors were exploring new regions of the world and gardeners were investigating whether foreign temperate plants would 'embellish and perfume our gardens with the elegance of their appearance and the fragrancy of their odours'.

The challenge of introducing plants to European gardens was non-trivial. Once plants had been collected, which was difficult enough, they had to be kept alive. The most practical means of transporting plants on long sea voyages was as seed; protecting seedlings or cuttings was fraught with problems. Once in Europe, methods had to be found to germinate the seeds and, if the plants were to become popular - propagated.

Hop tree, a small eastern North American tree, was apparently first introduced to Britain in 1704. However, it was not until the English plant collector Mark Catesby 'sent over a good quantity of seed from the Carolinas' in 1724 that it became firmly established in British gardens. Catesby's American travels (1722-26) were supported by men such as William Sherard and Charles Dubois. Sherard's reward was not only seed, some of which was grown in his brother's garden at Eltham Palace, but dried specimens for his herbarium. Sherard wanted the specimens for his own research into global plant diversity. Today, Sherard's herbarium specimens are part of Oxford University Herbaria.

As a garden plant, the hop tree is attractive because of its small size, very fragrant, mid-summer flowers and striking, winged, dry fruits. The tree's bark, leaves and fruit are bitter to the taste, and together with its aromatic properties, seems to have suggested to people the plant might have medicinal uses. The genus Ptelea, whose name is derived from a Greek common name for elm (fruits resemble those of elm), is a readily recognised member of the orange family. Delimitation of the species is more difficult; the species epithet refers to leaves divided into three parts but they may also have five parts. Leaves also vary in hairiness, size, texture and shape, producing multiple arguments about how to name formally this variation. Despite such academic disputes, within-species variation provides abundant material from which horticulturalists may select different garden forms.

In addition to its horticultural use, Native Americans made use of the hop tree, whilst the common name refers to the use of the bitter fruits as a hop substitute in beer.

Further reading

Bailey, VL 1960. Historical review of Ptelea trifoliata in botanical and medical literature. Economic Botany 14: 180-188.

Harris, SA 2011. Planting paradise: cultivating the garden 1501-1900. Bodleian Publishing.

Stephen Harris