The ash is a deciduous tree, which characterises the riparian area of Vale do Lourêdo. This tree can reach 35 metres of height, however, it usually does not exceed 20 metres. It has a tall and narrow trunk with a tall, dense and irregular crown. Its bark is grey and thick, with deep, narrow fissures, changing as it ages, becoming warty and dark grey with age. The leaves of the ash tree are bright green and compound (they look like several leaves on the same petiole), with an odd number of leaflets (5 to 13) in the shape of a lance, and with serrated margins. Its flowers are arranged in greenish-yellow pendant clusters and emerge before the appearance of leaves. Its very characteristic fruits are arranged in groups and are called samaras, having a seed surrounded by one or two spear-shaped, membranous wings of a brownish-yellow colour. When they fall, the shape of the fruits allows a better dispersion by the wind, following a characteristically helical movement.

This tree is common in almost the entire continental territory of Portugal, occurring mostly on watercourse banks and in riparian forests. It can also occur on the edges of wet grassland, alluvial plains and mudflats, and is generally associated with deciduous forest. This species prefers humid environments, presenting a high resistance to cold.

The ash tree is a species of high importance in riparian zones, due to the large extension of its roots, which contribute to the fixation of the soil, preventing erosion.

Other common names in Portuguese: freixo-comum, freixo-de-folhas-estreitas