This is a family made up of 27 genus and 700 species, mainly located in warm countries.

The most important from an allergologic perspective are Olive tree (Olea europea), Ash tree (Fraxinus excelsior), and to a lesser extent Ligustrum vulgare. Other plants belonging to this family are lilac and jasmine.

Olive trees are almost exclusively located in the Mediterranean shore, and in Spain mainly in the south and south-east zone of the Iberian Peninsula, and also in the Baleares islands (see map). Ash and Ligustrum are also located in the north of Europe.

Olive tree pollen is spheroidal, small (18-22 µm of diameter), and with a heavily reticulated surface. Olive trees generally flower in May-June, although the maximum pollinisation period is usually quite short (2-3 weeks).