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Frangula alnus, syn. Rhamnus frangula, the Alder Buckthorn, is a tall deciduous shrub in the family Rhamnaceae. It is native to Europe, northernmost Africa, and western Asia, from Ireland and Great Britain north to 68°N in Scandinavia, east to central Siberia and Xinjiang in western China, and south to northern Morocco, Turkey, and the Alborz and Caucasus Mountains; in the northwest of its range (Ireland, Scotland), it is rare and scattered. It is also introduced and naturalised in eastern North America

Taxonomy and namingEdit

Alder Buckthorn was first formally described by Linnaeus in 1753 as Rhamnus frangula. It was subsequently separated by Philip Miller in 1768 into the genus Frangula on the basis of its hermaphrodite flowers with a five-parted corolla (dioecious, and four-parted in Rhamnus); this restored the treatment of pre-Linnaean authors, notably Tournefort. Although much disputed historically, the separation of Frangula from Rhamnus is now widely accepted, being supported by recent genetic data though a few authorities still retain the genus within Rhamnus (e.g. the Flora of China).

The genus name Frangula refers to the brittle wood. Both the English and scientific species names refer to its commonly growing together with alders (Alnus) on damp sites. The name buckthorn refers to its close relationship to the genus Rhamnus, though Alder Buckthorn does not have thorns. Other recorded names include glossy buckthorn and breaking buckthorn; historically, it was sometimes called "dogwood" through confusion of the leaves with those of Dogwood Cornus sanguinea.

DescriptionEdit

Alder Buckthorn is a deciduous shrub, growing to 3–6 m, occasionally to 7 m tall. It is usually multistemmed, but rarely forms a small tree with a trunk diameter of up to 20 cm. The bark is dark blackish-brown, with bright lemon-yellow inner bark exposed if cut. The shoots are dark brown, the winter buds without bud scales, protected only by the densely hairy outer leaves The leaves are ovate, 3–7 (–11) cm long by 2.5–4 (–6) cm wide, slightly downy on the veins, with an entire margin, 6–10 pairs of prominently grooved veins, and an 8–15 mm petiole; they are arranged alternately on the stems. The flowers are small, 3–5 mm diameter, star-shaped with five greenish-white acute triangular petals, hermaphroditic, and insect pollinated, flowering in May to June in clusters of two to ten in the leaf axils. The fruit is a small black berry 6–10 mm diameter, ripening from green through red in late summer to dark purple or black in early autumn, containing two or three pale brown 5 mm seeds. The seeds are primarily dispersed by frugivorous birds, which readily eat the fruit.

EcologyEdit

Alder Buckthorn grows in wet soils in open woods, scrub, hedgerows and bogs, thriving well in sunlight and moderate shade, but less vigorously in dense shade; it prefers acidic soils though will also grow on neutral soils.

Frangula alnus is one of just two food plants (the other being Rhamnus cathartica) used by the Common Brimstone butterfly Gonepteryx rhamni. The flowers are valuable for bees, and the fruit an important food source for birds, particularly thrushes.

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