Perhaps the first point to make about Mountain Ash tree is that it is NOT a true ash at all. It is from the genus, Sorbus, while the true ash is of the genus, Fraxinus. This is important in that the Mountain Ash is, therefore, NOT susceptible to the Emerald ash borer which is devastating members of the genus, Fraxinus, across the American Midwest.

Mountain Ash are actually part of the Rosaceae Family and are more related to apple trees. This is also important to know because they also share many of the problems of apples such as apple scab and fireblight. These diseases plus other insect problems such as the Mountain Ash sawfly larvae make these trees a bit of a problem in many landscape situations.

Members of this genus are native to the more Northern zones of the world and are found in Northern Europe, North America and Asia. They have become popular in the home landscape because of the bunches of brightly colored fruit that appear in late summer. Most species have orange, red or yellow berries while some Asiatic species bear white fruit.

All Sorbus have leaves that are arranged in an alternate pattern along the stem. Some species have pinnately compound leaves while others have simple, lobed leaves. Small, not particularly showy, white flowers precede the appearance of the prized fruit. Most of the species have unspectacular reddish to yellow fall color.

The most commonly used members of this genus include S. americana (American Mountain Ash) and S. aucuparia (European Mountain Ash).

The Korean Mountain Ash (S. alnifolia) and the Cashmir Mountain Ash (S. cashmiriana) are noted for their larger individual flowers. The Cashmir type is also attractive for its pale pink flower buds and pinkish tinged flowers. Korean Mountain Ash also has smooth, gray bark similar to the European beech.

Species such as S. hybrida, S. foigneri and S. aria are known for the white tometose coloration on the bottom of their leaves. This adds to their ornamental value.