The Ledums were an independent genus for over 200 years, from the time of Linné, until molecular studies in the 1990s combined them with the rhododendrons (Rhododendron). Their close relationship is indicated by the numerous successful crossing between the formerly separate genera.
R. diversipilosum grows in Japan and on Sakhalin Island. It resembles Labrador tea (Ledum), with flowers similar in appearance and size, though the foliage is broader and larger, and the whole plant more robust. This Japanese species differs from the other Labrador tea species in the more acutely pointed leaves, whose undersurface is covered by a dense layer of short white hairs. In addition, there are long, rough, brown hairs on the leaf veins.
Rhododendron diversipilosum has a distinctive herbal smell similar to that of Labrador tea. The shrubs at Mustila were obtained through the Helsinki University collecting expedition to Hokkaido in 1993.