Frangula alnus

The alder buckthorn tree is in the buckthorn or Rhamnaceae family and is native to Europe, northernmost Africa and western Asia, from Ireland and Great Britain north to the 68th parallel in Scandinavia, east to central Siberia and Xinjiang province in western China, and south to northern Morocco, Turkey, and the Alborz in Iran. It also has been introduced to and is naturalised in eastern North America.

It is a non-spiny, multi-stemmed shrub up to 6 m tall.

• Bark is dark blackish-brown, with a bright lemon-yellow inner bark exposed if cut; shoots are dark brown; winter buds do not have bud scales and are protected only by the densely hairy outer leaves; unlike other "buckthorns", alder buckthorn does not have thorns.
• Leaves are deciduous, alternate, ovate, glossy, dark green, 3–7 cm long and 2.5–4 cm wide, with 6–10 pairs of prominently grooved and slightly downy veins; margin is entire (no teeth), petiole is 0.8–1.5 cm long; fall colour is not notable.
• Flowers are small, hermaphroditic, 3–5 mm in diameter, star-shaped with five greenish-white acute triangular petals, blossoming in May to June in clusters of 2–10 in the leaf axils.
• Fruit is a small black berry 6–10 mm in diameter, inedible, ripening from green to dark purple as they mature in July.
• 'Asplenifolia' is an upright, spreading, deciduous shrub 1.5–3 m tall. Its glossy green leaves are quite unusual in that they have the general appearance of fern pinnae: extremely narrow (to 7 cm long but only less than 1 cm wide) with irregular margins. It also sometimes is called fern-leaf buckthorn.