Thorny olive | The Morton Arboretum

Thorny olive is an exotic weed in Illinois. The Illinois Exotic Weed Act prohibits the sale or distribution of this plant in Illinois. This shrub or tree can spread by self-seeding or animal dispersal, as well as through suckering, which is the process of sprouting new growth from the base of the tree. It commonly grows in woods, prairies, and disturbed sites. This plant was introduced from Asia to the Southeastern United States, where it remains in abundance. The species was used specifically in disturbed areas in the United States for its ability to tolerate a variety of habitats. This tolerance helps it rapidly spread and maintain its robust growth system. The foliage of its long shoots can obstruct light, and its thorns assist the plant in completely covering neighboring plants. The thorny stems can also make physical removal difficult.

There are a number of native and non-native species that could be used in place of thorny olive. More desirable species may be found using the Search Trees and Plants page of the Arboretum website. Before purchasing or planting, be sure to check for any local or state guidelines on this species, and make sure that this plant is suitable for its habitat by checking its attributes at mortonarb.org or plants.usda.gov.

More Information

Size and Method of Spreading

Thorny olive is a medium to large shrub. It can grow between 3 and 25 feet. Its branches can spread to be over 15 feet wide. It can produce long shoots that can climb over other plants to spread further.

Bark Color and Texture

The shrub has thin, brown stems that may bear thorns about 2 inches long. Scales will occasionally appear along the stem.

Leaf Description

The alternate, simple, oval-shaped (ovate) leaves have a shiny appearance caused by the silver scales covering them. The leaves can also be green in color or have brown scales on the surface. They are usually rough to the touch, and have wavy leaf edges (undulate leaf margins).

Flower Description

The flowers of this shrub are small (about ½ inch), but fragrant. They are bell-shaped flowers, sometimes also covered in the silver scales that cover its branches. They form in clusters around the branches. Flowers occur in the fall.

Fruit Description

The dry fruit (achene) is oval shaped and covered by a fleshy layer giving it a drupe-like appearance, similar to a cherry. The fruit begins with a light green color, and matures to a deep red. The fruit also has scales on the surface before it ripens in the spring.