Saffron, crocus sativus, is the most expensive spice in the world. The reason for that is, that the only part which is used from the flower are the 3 pistils in the middle.
Saffron is cultivated for instance in Spain or South France. I bumped into in in Morocco. In a tiny village in Middle Atlas. Saffron from this region belongs to the best quality in the world, thanks to local climate and type of soil.
It is used for tea, tagines and many Moroccan dishes. It gives to the dishes not only pleasant taste, but attractive colour too. Though thanks to its price locals substitute it by orange food colorant in 99% cases.
It should be stored out of reach of light.
Recipes with saffron.