You don't have any Strawberry Trees do you (Arbutus unedo)? We have
samples of that honey here and it comes mainly from S. Europe, and
Corsica.

Looks quite normal, but has a horrid aftertaste like the cough medicine
I used to be given 30 or more years ago.

Sweet Chestnut is another possibility, especially if the honey is dark.

Needless to say there will be a whole host of uniquely N. American
species that will also fit the bill, but for 4 hives near an arboretum
it could be something from just about anywhere temperate.
--
Murray McGregor