University of Tennessee
Forest Resources AgResearch and Education Center
Our Center Home Page Arboretum Home Page Contact

Tigertail Spruce (Picea polita or Picea torano)

Tigertail Spruce A good example of a Tigertail Spruce is found in the Arboretum's Dwarf and Unusual Conifer Collection. It is endemic (restricted in distribution) to Japan. Branches of young trees are horizontal, but its common name comes from the pendulous branches of older trees that are said to resemble tiger tails. The stiff, green, sharp-tipped needles are borne on short woody, peg-like structures called pulvini. In winter Tigertail Spruce has conspicuous reddish buds at the end of its branches. Restrictions on importing Tigertail Spruce, Western Hemlock, and other conifers have been developed by Canada and several states to prevent further introduction of the Hemlock Wooly Adelgid, which has been devastating Eastern Hemlock forests.

Tigertail Spruce Cones The distinctive cones hang down, a characteristic that helps differentiate spruces from firs (Abies spp.) which have erect cones. The grayish-brown bark of Tigertail Spruce becomes deeply fissured in older trees. In Japan, this species has been used for lumber, paper pulp and ornamental purposes.

Return to Tree Table

Tree-of-Heaven (Ailanthus altissima)

Tree-of-Heaven Tree-of-Heaven Leaves Tree-of-Heaven Fruit
Tree-of-Heaven, a native of China, was first imported to Europe in the 1740's and subsequently was widely planted in many European cities. It was brought to the US in the 1780's and was planted as a street tree in many eastern cities because it is tolerant of smoke and soot and can thrive in poor soils. It gradually became naturalized and spread throughout much of North America. It is considered to be invasive in at least 30 states, including Tennessee where it is ranked as a 'Severe Threat' by the Tennessee Exotic Pest Plant Council. Tree-of-Heaven has alternate, very large (1-3 ft long), pinnately compound leaves with leaflets that have one or more glandular teeth near the base and no other teeth along their margins - a feature that distinguishes it from species of Sumac, Ash, and Black Walnut, all of which have teeth around the entire leaflet margins. This tree grows rapidly and reaches heights of 80-100 ft. It is dioecious, with small, pale yellow to greenish male and female flowers usually being borne on separate trees. It produces large numbers of flat, twisted, winged fruits, each with a single central seed. Its prolific production of seeds and its ability to sprout readily from roots after being cut back account for its invasive character. In addition, it is reported to produce toxic chemicals that inhibit the growth of other plants in its immediate vicinity. Tree-of-Heaven is not abundant at the Arboretum but is commonly seen along roads and greenways in the Oak Ridge area.

Return to Tree Table

Trillium (Trillium species)

Trillium grandiflorum Trillium cuneatum Trillium luteum
April brings with it a beautiful display of Trilliums along many of the Arboretum’s trails. There are at least three species of Trillium present: Large-Flowered Trillium (Trillium grandiflorum) has a stalked large white flower and large dark green leaves. Sweet Betsy (T. cuneatum) and Yellow Trillium (T. luteum) have upright sessile flowers (no stalk) and mottled leaves—they differ in flower color, with the former being maroon to bronze and the latter yellow. These plants are especially conspicuous along the Heath Cove and Oak-Hickory trails.

The name Trillium comes from a Greek word “tris” meaning three. The leaves and flower parts of Trillium all occur in “3s.” Species with sessile flowers (no flower stalks) are commonly known as “Toadshades,” while those with stalked flowers are known as “Wakerobins.” Trillium leaves are said to be edible, and the leaves and roots have been used for medicinal purposes.

Trillium grandiflorumAn interesting group of Trillium cuneatum and T. luteum is present along Old Kerr Hollow Road. This population has both yellow and maroon flowers, with others having intermediate colors between the two. Such populations may represent a hybrid swarm - i.e., a population of interbreeding hybrids.

Return to Wildflowers Table

Trumpet Creeper (Trumpet Vine) (Campsis radicans)

Trumpet Creeper (Trumpet Vine) Trumpet Creeper, a native woody vine also known as Trumpet Vine or Cow-Itch Vine, blooms in mid-June in our area. It is readily identified by its yellow-orange to scarlet tubular flowers and its large, pinnately compound leaves. A member of the Bignoniaceae, Trumpet Creeper is related to Cross Vine and Catalpa. The flowers are especially attractive to hummingbirds and butterflies that feed on the abundant nectar. Ants are also common visitors to these flowers. The vine can climb to heights of 40 feet, attaching itself to supporting trees or other vertical objects by modified aerial rootlets. It may also grow horizontally along the surface of the ground, thus being referred to by some folks as the "Devil's Shoestring." The common name "Cow-Itch Vine" reflects the fact that its sap can be a skin irritant. Although not commonly seen at the Arboretum, it is often seen along Greenway trails in Oak Ridge and elsewhere in our region. Trumpet Creeper grows rapidly and is considered to be potentially invasive.

Return to Shrubs and Vines Table

Tulip Poplar (Liriodendron tulipifera)

Tulip Poplar Flowers Tulip Poplar (also called Yellow Poplar) is the Tennessee state tree and a prominent member of the Arboretum’s deciduous forest. A member of the Magnolia Family, it is found throughout Eastern North America, from southwestern Ontario and Michigan, south to Louisiana and Florida. It is one of the largest native trees in U.S. eastern forests, growing to heights of 80 to 150 ft and is recognized by its tall straight trunks, its tulip-shaped flowers, and its distinctive 4-lobed, shiny green leaves that are pale underneath.

The thick bark of mature trees is deeply furrowed with narrow, rounded ridges. In May, the upright yellow-green, tulip-shaped flowers with a deep orange band near the base are found high in the tree canopy.

Tulip Poplar Leaves Tulip Poplar Bark

The light, brittle wood of Tulip Polar is used for furniture, plywood, oriented strand board (OSB), and pulpwood. Native Americans used the trunks to make dugout canoes. Tulip Poplar’s rapid growth and high commercial value for lumber make it suitable for reforestation.

After periods of above-average rainfall followed by dry conditions, such as we have had in 2017, Tulip Poplars may undergo premature leaf-yellowing and leaf drop. Prolonged periods of such conditions may result in the death of the trees. Recently, two large yellow poplar trees near the Arboretum’s Program Shelter died from such effects and have been removed.

Return to Tree Table

University of Tennessee - Forest Resources AgResearch and Education Center
901 South Illinois Avenue, Oak Ridge, Tennessee 37830 · Telephone: 865-483-3571 · Email: