Iceland flora: N.American species
 

In Iceland last week I briefly saw, and immediately lost track of, a
claim that only a single North American flowering plant species was
fully naturalized there. I assume this meant, if anything, that the
species had been first recorded a long time ago, and was not regarded
as a recent escape from cultivation. Can somebody please remind me, or
guess, what plant was probably referred to? A desultory Ggl hasn't
helped. The reference wasn't in a professional publication; the
accompanying photograph showed a dense stand of an apparently
low/medium plant with flowers in the red range.

--
Mike.