The University of Tennessee - Forest Resources Research and Education Center

A walk in the Marsh Area reveals a large colony of Lizard’s-Tail (also known as Water Dragon) growing along the creek bank. This aquatic plant has an inflorescence that resembles a bottle brush made up of a dense cluster of white flowers. As the fruits mature, the brown inflorescence is said to resemble a lizard’s tail.

Lizard-Tail grows along ditches, streams, ponds, and in other wetland situations. It is a popular water garden plant. Over time, the plant has been used as a general medicine for a variety of illnesses. Lignan compounds and other chemicals in Lizard-Tail have been shown to provide it with chemical defense against aquatic herbivores such as crayfish. Recent biochemical studies indicate that compounds from this plant have potential for treatment of tumors.

Buttonbush (Cephalanthus occidentalis)

In the first week of July, a Buttonbush located along Scarborough Creek near the entrance to the Arboretum displayed the impressive white spheres of tightly compressed flowers that give rise to its common name. This shrub, a member of the Madder Family (Rubiaceae), may grow to a height of 20 ft. Its leaves are mainly opposite, but whorls of three leaves may occur just below the inflorescence.

It occurs along the edges of wetland habitats such as stream banks and marshes from Southern Canada south to Florida and west to the Great Plains. It can also be found in New Mexico, Arizona, California and northern Mexico.

Although the leaves are poisonous to cattle, waterfowl and song birds eat the small nutlets, and the shrub provides excellent cover for a variety of birds and wildlife. Buttonbush has been used for medicinal purposes by Native Americans. The bark contains an alkaloid, cephaeline, which is used in medications to induce vomiting, but it also contains cephalanthin, a poison that dissolves blood corpuscles.

Black Cherry (Prunus serotina)

Early to Mid July

Black Cherry is commonly found along many trails at the Arboretum. Under a dense forest canopy, the trees are often small and shrub-sized with few flowers or fruits. Larger trees can be found in more open areas such as forest edges or forest openings where the fast-growing black cherries can better compete for light.

Black cherries which are relished by birds and other small animals have been ripening this past week. Birds distribute large numbers of the seeds widely. Trees loaded with fruit can be seen near the Program Shelter next to the dogwood plantings and just below the Shade Tree Orchard. The bark of young Black Cherries is smooth and reddish brown or gray with well-defined horizontal lenticels.

Older trees have more furrowed, platy bark which turns up at the edges. In the past, extracts of the bark have been used in cough medicines and various tonics. The leaves and twigs contain a cyanide compound which has been implicated in the death of horses and other livestock. The wood is used extensively for veneer, furniture, and lumber.

Japanese Stiltgrass (Microstegium vimineum)

One of the most aggressive invasive plant species in our region is Japanese Stiltgrass, also known as Nepalese Browntop. This annual grass, a native of Asia, was apparently introduced into Tennessee in the early 1900’s, possibly as discarded packing material used for shipping porcelain. Since then, it has become established in many eastern states and as far west as Texas. Japanese Stiltgrass grows in a variety of habitats and thrives under moderate shade where it outcompetes many native species. It produces many seeds which remain viable in the soil for at least 3 years.

Japanese Stiltgrass on the Forest Loop Road

Stiltgrass quickly colonizes areas where the natural forest floor’s leaf litter has been disturbed, such as along trail edges. Deer and livestock do not eat this grass, and it has been suggested that these animals preferentially select native species thus promoting the invasion of stiltgrass. Control of this species is challenging. Mechanical removal in late summer before seeds are produced can be effective. The UT Arboretum has been the site for two graduate student research projects investigating factors that affect the occurrence, rate of spread, and ecological impacts of stiltgrass in forested areas.

Climbing Fern (Lygodium palmatum)

Climbing Fern is an unusual plant found at a few locations on the Arboretum. It appears to be more of a vine than a fern. Its compound leaf (frond) consists of a twining, vine-like stalk (rachis) with sterile, palmate leaflets along its base and smaller fertile leaflets bearing sporangia toward its tip. The sterile leaflets (pinna) consist of a pair of palmate pinnules each of which has 5-10 lobes. These sterile pinna are evergreen and persist through the winter, while the fertile pinna die back. The climbing leaf can reach 3 meters in length. The genus Lygodium is mainly tropical, with L. palmatum being the only member native to North America. Two related species (L. japonicum and L. microphyllum) have been introduced into the southern US and are considered invasive. Climbing Fern is found throughout the eastern US, ranging from New England south to Florida, and west to the Mississippi River and Michigan’s Upper Peninsula. It is locally rare in most areas, but may be most abundant on the Cumberland Plateau. In the past it was collected extensively for Christmas decorations in New England and is considered a species requiring protection in many states.

Silk Tree or Mimosa (Albizia julibissin)

Silk Tree (commonly known as Mimosa) is found along highway and powerline rights-of-way, forest edges, and other disturbed areas. A native of Asia, it was introduced into North America as an ornamental during the 18th Century and is now considered an invasive plant — it is listed in the category “Severe Threat” by the Tennessee Exotic Pest Plant Council. A few trees occur at the Arboretum, but they have been managed as invasives and do not pose a significant problem. Silk Tree is a member of the bean family (Fabaceae) and has large twice-compound (bipinnate) leaves (up to 20 in. long); light to dark pink, thread-like flowers; and flat bean-like seed pods (5-7 in. long). The flowers attract hummingbirds, bees, and other insects. It is used as an ornamental throughout its range and has soil building properties related to nitrogen-fixing bacteria in its root nodules. Landscape ornamentals are susceptible to Mimosa Wilt which causes leaf yellowing and wilting in early and midsummer and results in death of the plants. Silk Tree produces abundant long-lived seeds, and it sprouts vigorously when cut back - features that promote its invasive character.

Boxelder (Acer negundo)

Boxelder is a relatively common tree along streams and other bottomland habitats but may also be found on drier sites. At the Arboretum it can be seen in several places such as along Old Kerr Hollow Road and near the lower end of Cemetery Ridge Trail. Its range includes much of North America and extends south to the mountains of Mexico and Guatemala. The pinnately compound leaves of Boxelder, typically with 5 to 7 toothed leaflets, distinguish it from other maples. Young trees often have only 3 leaflets and can be confused with poison ivy - however, Boxelder can be distinguished by its opposite leaves, green twigs with reddish brown upper surfaces, and lack of vine-like growth. This small to medium-sized tree (50-75 ft tall) is short-lived with an average age of 60 years. It is dioecious (the male and female flowers are borne on separate trees) and produces abundant fruits in drooping clusters that remain on the trees into the winter months. The winged seeds (samaras) provide food for birds and other wildlife. The brittle wood has limited value – it has been used for making boxes and low quality furniture. Its low heating value makes it a poor source for firewood. Boxelder is tolerant of drought and cold and, in the West, has been used as a street tree and for shelterbelts. Boxelder Bug, an insect associated primarily with female Boxelder trees, does relatively little damage to the trees, but as temperatures become colder in the fall, it may invade houses in large numbers and become an annoying pest.

Cornelian Cherry Dogwood (Cornus mas)

Cornelian Cherry Dogwood is a small tree or shrub native in southern or central Europe and western Asia. In these areas, the bright cherry-red fruit is used for syrup and preserves. As a landscape plant it can be used for a shrub border, hedge, screen, and foundation planting around large buildings. Its yellow flowers appear early in the spring before most other flowering shrubs, making it an attractive landscape feature.

An Arboretum research collection is present just west of the Juniper Collection. The project was initiated in 1997 to identify plants with exceptional ornamental value (flowering, fruiting, and form) that are hearty in this climate. Value to wildlife is also being considered. Seeds for these plants were collected from native trees growing in Romania and Croatia.

Chinese Privet (Ligustrum sinense)

Chinese Privet, an invasive, non-native shrub or small tree, is found in a variety of habitats at the Arboretum, including wetlands, upland forests, and disturbed areas. It is a native of Southeast Asia that was introduced into the US as an ornamental in the mid-1800’s and has subsequently spread throughout the East and Southeast. Once established, it produces vigorous root sprouts and can outcompete native species, completely taking over an area. Its abundant dark blue fruit is eaten by birds and other wildlife, and the seeds are widely dispersed by them.

A member of the Olive Family (Oleaceae), Chinese Privet is semi-evergreen with opposite leaves, gray bark, and dense clusters of fragrant white flowers in the spring. At the Arboretum, it is especially conspicuous in forest edges along Arboretum Drive, Cemetery Ridge trail, and as scattered clumps along Scarborough Creek. It is difficult to control, as it rapidly sprouts back from roots and stumps when cut back. Its leaves have a high content of phenolic compounds that protect it from insects and other herbivores. The UT Forest Resources Center, in cooperation with UT faculty, is presently engaged in the testing of new herbicides to help eradicate privet and other invasive, non-native plants.

Cucumber Tree (Magnolia acuminata)

Pinkish colored fruits of the Cucumber Tree near the entrance to the Visitors Center are apparent as one walks towards the entrance to Marsh Road. These cone-like fruits are initially green and said to resemble cucumbers, hence the common name. The yellow flowers that appeared in late April this year (2010) consist of six greenish-yellow tepals (sepals and petals are undifferentiated). The fruits mature in late summer to early autumn, producing reddish-orange seeds which may persist into winter.

Cucumber Tree is a native of Eastern North America ranging from southern Ontario to northern Florida. The wood is used for furniture, plywood, containers, and pallets. One source says the fruits have been used as flavoring for whiskey. The bark was used for a variety of medicinal purposes by the Cherokee and Iroquois peoples.

Cranefly Orchid (Tipularia discolor)

Mid - to Late July

If you look carefully along a number of our Arboretum trails, you may be fortunate enough to see an inconspicuous orchid that blooms in mid– to late July. The leaves of the Cranefly Orchid, which develop late in the fall, are distinctive in being green on the upper surface and purple below. The leaves persist during the winter months allowing the plant to photosynthesize during the season when sunlight reaches the deciduous forest floor. In the spring, the leaves break down and are absent at the time of flowering. Tipularia discolor, the only member of its genus in North America, is found in many parts of Tennessee and is distributed from southern New England, south to Florida, and west as far as Texas.

Hardy Orange (Poncirus trifoliata)

An unusual and interesting shrub is located at the edge of the Shade Tree Collection near the top of the Tulip Poplar Trail Spur. Hardy Orange (or Trifoliate Orange) is a member of the Rutaceae plant family and closely related to the Citrus genus. It is a native of China and Korea that has been introduced into the US. In parts of the Southeast, it has escaped cultivation and can be an invasive species in fencerows, roadsides, and forest edges. The compound leaves have three leaflets, and the branches terminate in conspicuous thorns.

Although the green fruit, which turns dull yellow in the fall, has been used for making marmalade, it may cause severe stomach pain, nausea, and skin irritation. Hardy Orange is a cold hardy, disease resistant plant that is used as a root stock for commercial citrus. Historically, it was planted for hedgerows because its vicious thorns make it virtually impenetrable. Thus its presence can indicate abandoned home sites.

Devil's Walking Stick (Aralia spinosa)

Mid-July to Mid-August

As you walk to the end of Marsh Road, look to the right for a dense thicket of Devil’s Walking Club that exhibits large terminal clusters of creamy white flowers and large compound leaves. This relatively small tree gets its name from the club-shaped branches and the “vicious” prickles along the trunk, especially at the nodes. The prickles only form during the first year of growth, and as the tree matures the older stems gradually lose their prickles.

Leaves are doubly or triply compound and may be up to 5 feet in length, with individual leaflets 2-4 inches long. The purple to black fruits mature in late summer and early fall and are eaten and dispersed by birds; the foliage may be browsed by deer. Devil’s Walking Stick is native to the southeast, but has been successfully introduced to many other parts of the eastern U.S.

Lizard's Tail (Saururus cernuus)

Buttonbush (Cephalanthus occidentalis)

Black Cherry (Prunus serotina)

Japanese Stiltgrass (Microstegium vimineum)

Climbing Fern (Lygodium palmatum)

Silk Tree or Mimosa (Albizia julibissin)

Boxelder (Acer negundo)

Cornelian Cherry Dogwood (Cornus mas)

Chinese Privet (Ligustrum sinense)

Cucumber Tree (Magnolia acuminata)

Cranefly Orchid (Tipularia discolor)

Hardy Orange (Poncirus trifoliata)

Devil's Walking Stick (Aralia spinosa)