Rhododendron 'Catawbiense Boursault'
The Boursault Catawba Rhododendron is an old, hardy variety. Possibly not as hardy as the ironclads, it is nevertheless recommended in, for example, the Northeast USA. According to Hachmann of Germany, it can withstand temperatures of -30oC. The Boursault Catawba Rhododendron is a choice of several R. catawbiense hybrids prior to 1849, but the precise genome is not known.