The genus Halesia comprises three species (two from North America and one from China), and is one of the genera that reveal the ancient affinities of the floras of North America and China. In British horticulture, the genus is represented almost exclusively by the beautiful Halesia carolina. Yet, as spectacular as this tree can be in the spring, the more recently introduced Halesia monticola is finer still. The Chinese Halesia macgregorii is poorly known and, from a horticultural viewpoint, its flowers do not equal those of its North American cousins.
Not everybody agrees the genus comprises just three species; some researchers accept more species. Part of the controversy over species numbers concerns the complex patterns of variation shown by the North American species, especially Halesia carolina, across their native ranges.
A native of the south-eastern United States, Halesia carolina is a small, deciduous, understorey tree or occasionally a shrub. It has a broad, rounded crown and is typically less than 10 m tall. The alternate leaves have serrate margins. The nodding bell-shaped, white flowers, borne in clusters on one-year-old branches, appear in April and May producing magnificent floral displays shortly before the leaves emerge. In the autumn, brownish fruits are produced. These lantern-like structures, which can be up to four centimetres long, have four prominent wings that run along their entire length. The fruits often persist into late winter, on the otherwise bare twigs.
The genus was first raised in Britain in 1756 by the Irish linen merchant John Ellis from seed sent from South Carolina, USA, by the young physician Alexander Garden. Ellis named the genus in honour of the eighteenth-century English clergyman Stephen Hales, a pioneer in our scientific understanding of animal and plant physiology, and the name was formally published by Carolus Linnaeus. Before Ellis managed to cultivate Halesia, the genus was known from herbarium specimens and drawings, such as those made by the plant collector and artist Mark Catesby in the Carolinas in the 1720s.
In British gardens, Halesia carolina prefers moist, acidic, humus-rich soils in partial shade and ideally, a hot summer. At the Harcourt Arboretum, specimens can be found on the Serpentine Ride, their rich yellow autumn colours giving way to the unusual fruits throughout the winter. In late spring, the flowers become the tree's main interest. Other members of the Styracaceae grown in British gardens include species of Pterostyrax, Rhederodendron, Sinojackia and Styrax.
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