ORIGIN: East Asia

PATHWAYS: horticulture, silviculture

POSSIBLE TO DETECT: year-round

FLOWERING SEASON: May – June

DESCRIPTION: Dioecious, deciduous tree with thick branches. Bark smooth, greyish. Leaves 30–90 cm long, spiralling, glabrous, pinnately compound. Leaflets lanceolate, pointed at the tip, with 2–4 glandular lobes near the base. Leaflets, male flowers and young shoots have a foul odour. Flowers are small, borne in large, dense, upright clusters. Fruits are lanceolate samaras several centimetres long with a seed in the centre. They develop on female plants and persist on trees until the following spring.

HABITAT: Forest margins and open forests, including riparian forests and open rocky slopes. Also established at ruderal sites, along roadsides and in urban habitats.

STATUS: Widely established throughout Europe, particularly common in the Mediterranean region and in urban areas. In Slovenia it is common in lowland and hilly regions, especially in central and eastern Slovenia. A major problem in urban environments, because it is germinating in small cracks (e.g. in walls and between tiles in the pavement) and on abandoned agricultural sites. 

SIMILAR SPECIES: European ash (Fraxinus excelsior) black walnut (Juglans nigra), Manchurian walnut (J. mandshurica) and staghorn sumac (Rhus typhina) do not have glandular lobes on leaflet bases. Staghorn sumac has fuzzy leaflets with serrate margins and upright clusters of fruits.

SOURCE: Field Guide to Invasive Alien Species in European Forests