Two years ago I was taken to visit this site, and I returned in May this year as part of a botanical project to monitor its spread. The species here is a different one - Ledum groenlandicum (or L. palustre ssp. groenlandicum) - which also grows in Greenland although I had not seen it there. The chief difference is that L. groenlandicum has broader leaves.
Also L. groenlandicum usually has 6-8 stamens while L. palustre has 10.
It is generally considered that it was introduced at this site, though this is difficult to verify and it has been present in the area for at least 150 years.
The plant is closely related to the Rhododendrons and is now frequently included in the genus Rhododendron rather than Ledum. The leaves are used to make tea in some parts of north America, though they contain toxins.
The site is rich in other interesting species, and one of the most abundant is Cranberry (Vaccinium oxycoccos).
These tiny flowers grow on thread-like stems with narrow leaves, and often carpet the ground.
The berries form later in the year, and are disproportionately large compared to the size of the plant.