Trapwell pipes marked with "World's best briar" are made of Mountain Laurel (Kalmia latifolia) a species from the Ericaceae family.
The brand was made by D & P Pipe Works, owned by D. P. Levitas and located in Sparta, Alleghany County, North Carolina close to the population of Mountain Laurel in the area. Later, this company changed its name to Sparta Pipe Works and still later to Sparta Industries.
There were at least three pipe brands made from the Mountain Laurel: Trapwell, Breezewood and Custombilt.
This information courtesy Pipephil