Difference in Ash & Alder

Geography

• Most of the native alders in North America grow on the West Coast or in the Pacific Northwest, including species such as Sitka alder, white alder and thinleaf alder. Alders like speckled alder exist across much of Canada and into the Northeast, while hazel alder is a tree or large shrub of the eastern states. Many alders used in landscaping are introduced species, such as black alder. The ash trees have representative species in nearly every corner of the United States, with ashes such as white ash and green ash possessing huge distributions across much of the eastern United States. More localized ash trees include types like Texas ash in Texas and Oklahoma and the singleleaf ash of the Southwest.

Flowers and Fruit

• The alders have male and female flowers on the same tree, a trait of the Birch family. The male flowers are drooping and tassel-like, called catkins. The female flowers look more like a cone and develop small fruits called nutlets. The ashes feature male and female flowers on separate trees. These flowers usually have no petals, writes C. Frank Brockman in "Trees of North America," and the female trees yield seeds known as samaras in clusters. The samaras, which can be messy, look like miniature oars. Landscapers sometimes choose male ash trees for planting to avoid the mess associated with the female specimens.

Leaves

• Alders have simple leaves with prominent veins and teeth along the edges. They are usually oblong, oval or elliptical. The leaves of ashes are compound leaves, with a central stem to which several leaflets attach to compose one single leaf. The number, size and shape of the leaflets depend upon the species of ash tree. For instance, white ash has between five and nine leaflets on a central stem that can be as long as 15 inches, with each leaflets between 2 and 6 inches in length. Ash leaves can add significant color to a fall landscape, unlike the alders.

Uses

• The shrubby nature of many alders makes them appropriate choices to fill in areas where few other trees grow. Black alder does well in both dry sites or in low, damp areas. Italian alder has use as a windbreak, notes the Missouri Botanical Garden. The ashes work as lawn trees, street trees or shade trees. Some of the bigger species, including white ash, are suitable specimens for large landscapes, like campuses or parks, according to the University of Connecticut Plant Database.