European Mountain Ash forms a small tree up to 40 feet high or can grow as a large shrub in certain conditions. When found as a tree in the southern parts of its range, it has slender, but multiple trunks and an elliptical crown with ascending branches.
The bark is smooth when young, almost yellowish-green, with numerous lenticels but becoming grayish-brown to bronze and scaly with some splits and cracks with age.
Twigs are somewhat stout, reddish-brown with fine hair when young. Leaf scars are narrow but encircle half the circumference of the twig. Buds reddish-brown, hairy with long gray hair at the tips, not sticky. Terminal buds are larger, laterals more pointed and often curved toward the twig.
The leaves are alternate and pinnately compound with an odd number of flat oblong to lanceolate leaflets, each 1-1/2 to 2-1/2 inches long and usually not more than 3/4 as wide, with a length to width ratio of usually less than 3 to 1 [2.4 to 1 at least and at most 3.7 to 1]; the entire leaf usually consisting of 11 to 17 leaflets. These are sessile or with very short stalks. Leaflet tips are more rounded, acute to obtuse, than the other two species compared below. The margins of leaflets are serrate, but not all the way to the base, which is slightly asymmetrical, the underside much paler in color due to dense fine hair. The central rachis of the leaf is somewhat flattened giving angled edges. At the base of each leaf is a pair of green stipules with sharply toothed margins; these may drop away or persist on the leaf stem. Leaves turn yellow in the fall.
The inflorescence is a flattened cluster (a corymb) of small white flowers, at the end of branches; the clusters can be 5+ inches wide. Stalks are hairy.
Flowers: Each flower is stalked, about 3/8 inch wide with 5 rounded white petals that have narrowed bases. The flowers are perfect, with 15 to 20 stamens that have white filaments and yellow anthers that turn reddish-brown when shedding pollen. There are 3 to 4 styles. The central receptacle is yellow-green in color. The hypanthium base around the receptacle has dense fine hair as does the flower stalk. The outer 5 short sepals are also yellow green and have pointed lobes.
Fruit: Fertile flowers mature to 3/8 inch diameter orange-red pomes which will remain on the tree until eaten by birds or sometime overwinter. The sepals remain on the bottom of the pome and resemble a dark 5-pointed star. The seeds contained in the pome are reddish, tear-drop shaped with a pointed beak. Seeds are toxic - see notes a bottom of the page.
Habitat: European Mountain Ash grows best in well drained soils in full sun and will tolerate some dryness. Being a northern species it does not do well where the summers are too hot (i.e., the southern half of the U.S. south of Zones 5 to 6). Trees can be affected by bacterial fireblight which causes dried up leaves at the end of branches. Several cultivars are available from the nursery trade that seen to grow well in Minnesota: "Cardinal Royal" and "Edulis".
Names: The genus name Sorbus is taken from the Latin sorbum referring to the fruit of a tree similar to the Mountain ashes. The species name, aucuparia, is specific to this tree and was derived from Latin roots which became aucupor, meaning "to go bird-watching," which had to do with the use of the fruit of the tree to lure and catch birds. The author name of the plant classification, 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: S. aucuparia is distinguished from the two other species of Sorbus that grow in Minnesota as follows: S. decora, Showy Mountain Ash, also has leaflets that average less than 3x as long as wide but do not have dense fine hair on the underside, nor does the flower hypanthium have dense fine hair. The leaflet tip is abruptly tapered to a projecting tooth; twig buds are stickly; the flowers and the fruit are the same size. S. aucuparia has the widest leaflets which are also hairy on the underside. S. americana, American Mountain Ash, has lateral leaflets averaging more than 3x as long as wide and are finely hairy beneath on the veins. Flowers and fruit are smaller. Twig buds are a dark reddish-purple and sticky.
Above: 1st photo - The inflorescence is a flattened cluster at the end of branches. 2nd photo (and below) - The white flowers have 15 or more stamens and a yellow-green central receptacle. 3rd photo - Stalks of the corymb and individual flower stalks have fine hair. The cup-shaped hypanthium has yellow-green lobes slightly shorter than the white petals.
Below: Mature plants can reach 40 feet in height. This example has been grown with a single trunk.
Below: 1st photo - Bark become grayish-brown at maturity with some splits. 2nd photo - Twigs are reddish brown as are the buds which have gray hair. Leaf scars are narrow but encircle half the twig.
Above and below 1st photo: Fruit clusters of orange-red pomes form in mid-summer. The remains of the sepals form a dark 5-pointed star at the base of each pome. 2nd photo -the leaf is pinnately compound with 11 to 17 leaflets.
Below: 1st photo - Each leaflet has serrated margins, but the serrations not entirely reaching the base, which is asymmetrical. 2nd photo - The underside is paler in color with fine hair. 3rd photo - Each full leaf has a pair of toothed stipules at the base.
European Mountain Ash is found across the northern half of the U. S. from the east coast to the west coast and in Canada in the lower Provinces except Manitoba. The species was introduced from Europe as an ornamental and has been widely planted for that purpose, resulting in some naturalization in native areas. It is found in Minnesota in such areas in at least 10 counties, half of which are in the greater metro area. Other than some susceptibility to fireblight, it can make a good landscape specimen as it will grown in areas south of where the native American Mountain Ash grows.
It is unclear when the species arrived at the Garden, but one is found along the North fence.
Toxicity: Seeds contain up to 22% of a fixed oil that can cause poisoning. (Ref. #7)
Medicinal and other uses: The bark was used by herbalists to create a decoction for treating diarrhoea; the berries were used to make a gargle for sore throat and due to their anti-scorbutic properties, used to prevent scurvy. All parts of the tree are astringent. The bark has been used to make a black dye. The fruit, less the seeds, is said to make a good jelly as they contain acids and sugars. They used to be dried for flour and for making ale when fermented. See Mrs. Grieve (Ref. #7) for more details.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"