They grow to tall, and have alternate, simple ovate leaves 5–16 cm long and 3–8 cm broad. The flowers are pendulous, white or pale pink, produced in open clusters of 2–6 flowers, each flower's being 1–3 cm long. The fruit is a distinctive, oblong dry drupe 2–4 cm long. All species except H. diptera have four narrow longitudinal ribs or wings on fruit; diptera only has two, making it the most distinctive of the group.
Species
Halesia carolina L.; little silverbell – eastern North America
Halesia macgregorii Chun; Chinese silverbell or Macgregor's silverbell – eastern China
Halesia tetraptera L.; common silverbell – eastern North America;
which includes a variety treated by some as a full species:
Halesia monticola Sarg.; mountain silverbell – southern Appalachians and southwards A.E.Murray; H. tetraptera var. monticolacf.
Halesia monticola is the largest of the genus, with specimens up to tall known in the Great Smoky Mountains National Park in North Carolina; the second-largest is H. macgregorii, reaching in China. The others rarely exceed tall. H. monticola is considered by some to be a subspecies of H. carolina. However, there appears to be a consistent size difference between the two taxa.
Taxonomy
The taxonomy and naming of the American species is confused and extensively disputed. The first dispute is over the exact identity of the specimen first named by Linnaeus as H. carolina; some contend that it is the same as H. parviflora, while others say it is the same as H. tetraptera. The second dispute is over whether H. monticola is sufficiently distinct from the other species to merit specific recognition or not. Neither question has yet been conclusively answered. The treatment here includes both H. carolina and H. monticola. A phylogenetic study suggests that Halesia is not monophyletic and as a result, the Chinese species Halesia macgregorii has been transferred into a new genus Perkinsiodendron, named after American botanist and Styracaceae expert Janet Russell Perkins. The genus was named after Stephen Hales by John Ellis, publishing the name in the tenth edition of Linnaeus's Systema Naturae in 1759. The name is conserved as the same name had been used in an obscure earlier publication in 1756 for a different plant.
