| Halesia, Halesia carolina, Halesia tetraptera, Halesia diptera, Styracaceae|
Halesia (tetraptera var.) monticola, or mountain silverbell, was originally included in H. carolina, but was identified first as a subspecies by Rehder in 1914, then as a species by Sargent in 1921. More recently, some authoritative sources regard it only as a subspecies or variety, while other authoritative sources regard it as a species, as it is treated here.
Halesia monticola Wikipedia
H. monticola is much larger than either the little silverbell or common silverbell (var. tetraptera), and is the largest member of the genus. It is known to grow 24 meters tall in the Great Smoky Mountains. Another important difference is that monticola has significantly larger flowers than either H. carolina or H. tetraptera.
The silverbell tree grows mostly in the southern Appalachian Mountains and into southern Alabama and Georgia, with small outlying populations up to and barely north of the Ohio River, and along the Oklahoma-Arkansas border. It is apparently absent from Mississippi and Louisiana. In the cited reference, this species is referred to as Halesia carolina.
The mountain silverbell is cultivated in many places around the world. Although it may be difficult to transplant, once established it is easy to grow. It blooms while still quite small, only about 4 meters tall.