Elder Sambucus niger is a common small tree in the Touraine. The wood is soft, so it doesn't have a commercial value. But from May to early July elder produces gazillions of tiny creamy white flowers held in flat clusters all over the tree, fragrant and smothered in yellow pollen.
The flowers have been used as part of the suite of ancient herbal remedies in Europe for centuries, for coughs and colds. Modern research suggests that they may indeed be effective against sinusitus, and can lower blood sugar.
The flowers can be used to make a subtle but delicious variation on lemonade. Pick them while they are at their peak, and have plenty of pollen still. My recipe for elder flower syrup is here. You can bottle it as above or freeze it in icecube trays and use it from frozen (this brilliant suggestion comes from our friend Roger).