This is a very rare species that in the Netherlands only lives in a small area of Southern Limburg where the soil has been poluted with zinc and other heavy metals.
These metals are brought to this area by the small river de Geul and there is a whole unique flora surrounding this area and the heavy metals.

The flowers are practicaly always yellow but in rare cases can also have blue upper petals.
In some populations outside of the Netherlands this blue forms is far more common.