Plant 205

Stewartia species (Theaceae)



The genus Stewartia comprises about twenty species of deciduous or evergreen, large-flowered trees, naturally distributed in the southeastern United States and East Asia. In their native ranges, stewartias are found in low elevation or montane woodlands on acidic soils. Since their first discovery, stewartias have attracted the attention of horticulturalists. In addition to their form and camellia-like flowers, some stewartias are valued for their autumn colour and bark.

Traditionally treated as one genus, evergreen stewartias are sometimes separated from Stewartia into a separate genus, Hartia. Pollen data have been used to suggest further division of Stewartia into three groups, Hartia, Old World Stewartia, and New World Stewartia. However, there is little evidence from DNA to support recognition of evergreen stewartias as a separate genus.

Stewartia malacodendron, one of only two North American species, was first described by the Swedish botanist Carolus Linnaeus. The tree was introduced to Britain in the early eighteenth century by the Colonial botanist and collector of Virginian plants John Clayton; it first flowered in 1792. This tree's requirement for summer heat, despite its spectacular flowers, is probably responsible for it rarely being cultivated in Britain. Much commoner is the second deciduous North American species, Stewartia ovata, a late-eighteenth-century introduction with a broader altitudinal range than Stewartia malacodendron.

However, the most widely-grown stewartia is the late-nineteenth-century introduction Stewartia pseudocamellia, a deciduous species native to Japan and the Korean Peninsula, where it extends from about 200 metres to 1500 metres above sea level. As might be expected, this species tolerates a wide range of temperatures, and has given rise to many named horticultural cultivars. It produces pure white flowers, up to ten centimetres in diameter, which become tinged with red following pollination.

Linnaeus used the generic name to commemorate the botanical interests of the eighteenth-century Scottish nobleman John Stuart, third Earl of Bute. He had seen an illustration of Stewartia malacodendron, growing in the garden of Stuart's London home, made by the artist Georg Dionysius Ehret. However, the painting was poorly labelled and labelled with the name 'Stewart' rather than 'Stuart'. Consequently, the genus Stewartia was erected. In the late eighteenth century, the French botanist Charles L'Héritier corrected the mistake and created the genus Stuartia, the name that was applied until well into the twentieth century, especially in Britain. However, the rules of botanical nomenclature mean such errors cannot be corrected, hence Stewartia also commemorates a spelling mistake.

Further reading

Bean WJ 1980. Trees and shrubs hardy in the British Isles. Vol. 4. John Murray.

Heo, K-I et al. 2011. Generic delimitation and infrageneric classification of Stewartia and Hartia (Theaceae; Stewartieae): insight from pollen morphology. Plant Systematics and Evolution 297: 33.

Stephen Harris