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.
American Hornbeam (Carpinus caroliniana)
Late July to October
American hornbeam (also known as ironwood, muscle-wood, blue beech) grows abundantly along Old Kerr Hollow Road. At this time of year the maturing fruit clusters hang down from the canopy. These consist of a 4-6 inch stalk with a series of 3-lobed, leaf-like bracts — the small nutlets are found at the base of these bracts. A related tree, European Hornbeam, is found along the Heath Cove Trail.
Common names of this tree are related to its bark and wood. The dense wood dulls woodworking tools (ironwood) and takes a horn-like polish (hornbeam). The muscle-like bark has sinewy, muscle-like ripples, (muscle-wood) and its otherwise smooth, blue-gray appearance resembles beech bark (blue-beech). The wood has been used for tool handles, bowls, and ox yokes. The fruits and buds are eaten by birds, squirrels, and deer. This understory tree occurs along streams and other low areas throughout the eastern U.S.
Black Walnut (Juglans nigra)
Early August
Black Walnut, a relatively common tree at the Arboretum, is readily recognized by its large, pinnately compound leaves with 11-23 leaflets, its dark (almost black) ridged to platy bark, and its green (turning to yellow), ball-shaped fruits. It is considered a pioneer species invading fields and other open areas where it grows rapidly.
Black Walnut is an allelopathic plant, producing a chemical compound, hydrojuglone. When hydrojuglone is oxidized in air or soil, it becomes the toxic chemical juglone. This toxin (produced from the leaves, fruits, and roots) accumulates in the soil under the tree, inhibiting the growth of most other plants. A few plants, especially grasses, are unaffected by juglone and can grow under the tree canopy.
Black Walnut is a highly prized wood. Early settlers used it extensively for construction, but today it is primarily used for making furniture and gunstocks. The nuts are used in cooking, the oily husks have been used to make dyes and walnut stain, and the pulverized shells are used in oil drilling, cleaning jet engines, and for making activated charcoal.
The presence of black walnut trees at various sites around the Arboretum often indicates the location of former home sites. The fruits from these trees appear to be somewhat larger than normal, perhaps reflecting a selection by the homeowners of more vigorous cultivars.
Elms (Ulmus spp.)
Mid August
Four native species of Elms are found in East Tennessee — American Elm, Winged Elm, Slippery Elm, and Rock Elm. Beginning in the 1930’s, Dutch Elm Disease, caused by a fungus, has greatly reduced the populations of these trees. American Elm, once the major shade tree in towns throughout the Midwest and East, has been virtually eliminated by this pathogen. Three species of elm found along Arboretum trails are briefly described below.
Winged Elm (Ulmus alata) is a relatively small tree growing to heights of 40-50 ft. Distinguishing characteristics include relatively small (1½ - 3½ inches long), narrow, coarsely toothed leaves and thin, corky ridges along many of its branches - the wings that are the basis for its common name. Winged elm is found along the lower parts of Cemetery Ridge Trail.
Slippery Elm (Ulmus rubra) is fairly common along Old Kerr Hollow Road. The leaves are up to 7 inches long, and their upper surface is rough, feeling like sandpaper. Its common name refers to the fact that its inner bark has a very slippery, mucilaginous sap. If you scratch a leaf petiole and run a
finger along the split, you can feel its slipperiness. Slippery Elm grows to heights of 60-70 ft.
Rock Elm (Ulmus thomasii) is present along the upper portions of Cemetery Ridge Trail and the South Forest Loop Road. Its leaves are relatively smooth in texture and 2-4 in. long. Rock Elm is also called Cork Elm because of the
irregular corky wings that develop on older branches. It can grow to heights of 100 ft. Although present in East Tennessee, Rock Elm is more common in middle Tennessee. In our area, it is typically found on relatively dry, rocky sites.
Hollow Joe Pye Weed (Eupatorium fistulosum)
Mid August
Hollow Joe Pye Weed, a member of the Aster Family with a head of pink disk flowers (no ray flowers), can be seen along Scarboro Creek near the Arboretum entrance. This type of Joe Pye Weed (also called Trumpet Weed) grows up to 10 ft in height and can be distinguished from similar Eupatorium species by its purplish
colored, hollow stems, and whorls of 4-7 simple leaves at each node of the stem. This plant is attractive to many insect pollinators such as butterflies, bees, and wasps.
Other types of Joe Pye Weed include Sweet-scented Joe Pye Weed (E. purpureum), a more northern species with solid green stems and 3-4 leaves at each node, and the smaller Spotted Joe Pye Weed (E. maculatum), with spotted purple, solid stems and flat-topped flower heads.
Various accounts have identified Joe Pye as an Algonquin Indian or a white man who used the plant for treating typhus. The hollow stems were used as straws and blow guns. The plant was also used for a variety of internal and external medicinal uses. Apparently there is little, if any, scientific support for its medicinal values. Hollow Joe Pye Weed is found in moist areas along streams, ditches, and roadsides, and in upland fields and meadows.
Black Gum (Nyssa sylvatica)
Mid to Late August
Blackgum (also called Black Tupelo or Sourgum) is a common tree in our
Arboretum forests. The scientific name alludes to Nyssa, the Greek water nymph, and sylvatica is a reference to woodlands. The origin of the common name “Blackgum” is unclear but may
refer to the dark blue-purple fruit. The shiny, alternate leaves are usually
elliptic in shape, often wider above the middle with a pointed tip, and from 2-5 in. long. In the fall they turn red,
orange, or almost purple.
The branches grow out perpendicular to the trunk, somewhat resembling the spokes on a wheel, and older branches tend to droop. The trees are either predominately male or female, but often a few flowers of the opposite sex are present. The small, dark blue fruits (drupes) are found in the fall — this year our trees appear to be bearing few, if any, fruits. The fleshy fruit is eaten by birds, squirrels, and other small mammals, while young leaves
provide forage for deer. The tree may grow to heights of 60-100 ft., and can live to be over 400 years old.
Northern Catalpa (Catalpa speciosa)
Late August
Two large Northern Catalpa trees (also known as Indian Bean Tree or Cigar Tree) are found near the Juniper Collection, east of the Arboretum Program Shelter. The genus name Catalpa purportedly comes from a Cherokee Indian word for “bean tree” — the seed pod, which is conspicuous at this time of year, has a long, bean-like shape. Catalpa belongs to the Bignoniacea family, which also includes Cross Vine and Trumpet Creeper.
The natural range for Northern Catalpa includes western Tennessee and other parts of the Central Mississippi Valley. It has been widely planted in urban areas and on farms to provide materials for fence posts. The showy white flowers that give rise to the elongate seed pods appear in late spring.
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