University of Tennessee Forest Resources Research Center

Numerous small white flowers are conspicuous along the Oak-Hickory Trail this week (April 5-12). Rue Anemone, or Wind Flower, belongs to the buttercup family. The basal leaves are divided into nine leaflets, each of which has three rounded lobes. The flowers are white to pinkish with several flowers being borne in an umbel - i.e., a long flower stalk with several branches originating from a common point. These plants can also be seen at a low point along the Cemetery Ridge Trail, in the same general location as the Roundlobe Hepatica seen in late March.

Other wildflowers soon to come include Mayapple (palmate leaves have emerged), Fly Poison (dark green clusters of basal leaves are particularly conspicuous along the Oak-Hickory Trail), and Violets. Red Maples have been in bloom since early March, and the red flowers parts have been, and are being, shed along the trails. The Magnolia Orchard is nearing its peak bloom, and the ground is covered with purple, red, pink, and white tepals (showy petals and sepals that are undifferentiated).

Redbud (Cercis canadensis)

One of the most beautiful and conspicuous trees at the Arboretum in April is the Redbud. This tree is most commonly seen at forest edges, in disturbed areas, or in managed landscapes. Redbud is a member of the bean family (Fabaceae), and in a natural setting is an early invader of disturbed areas where it grows quickly but is generally short lived (20-25 years). Distinguishing characteristics of Redbud include its rose-pink, pea-like flowers, its heart-shaped leaves, and its flat, brown, bean-like pods.

At the Arboretum you will see Redbud along several trails and bordering some open areas. A research planting near the Program Shelter is in full bloom. The larger trees in this area are survivors of a failed research study originally planted in 1995. A new planting of redbuds was made in 2007 next to these older trees; the young trees are just becoming established. The objective of the current study is to evaluate Chinese Redbuds and ones from a northern location in the United States for potential introduction in Eastern Tennessee.

Flowering Dogwood (Cornus florida)

Flowering Dogwood is most conspicuous in the spring with its bright flowers composed of four large white bracts surrounding the small yellow flowers.

The Arboretum hosts several research collections of dogwood. An extensive collection of dogwood species and cultivars near the Program Shelter provides researchers with genetic material to breed new dogwood varieties. Additional research collections of Flowering Dogwood (Cornus florida) and Kousa Dogwood (Cornus kousa) are found along the lower portion of Arboretum Drive where it merges with Old Kerr Hollow Road. The Arboretum also has an extensive research collections of Cornealian Cherry Dogwood (Cornus mas).

In the fall, Dogwood also provides red to mauve leaf colors and bright red fruits that are eagerly harvested by a variety of birds and squirrels.

Purpleblow Maple (Acer truncatum)

A variety of ornamental maples are planted in the Arboretum’s Shade Tree Collection. One of these, the Purpleblow Maple (also called Shantung Maple), produces a conspicuous display of greenish-yellow flowers in late March and early April. This tree, native to China, Manchuria, and Korea, grows to heights of 20 to 25 ft., with a broad, rounded crown. Its distinctive green leaves have three prominent sharp lobes with two smaller lobes along the flattened (or truncated) base. The samaras (two-winged, two-seeded fruits) are 1 to 1.5 in. long. The bark of young trees is smooth and often has a purplish hue, but it becomes ridged as the tree matures. In the fall, the leaves turn yellow to orange with prominent dark red leaf veins.

Several cultivars have been developed with distinctive yellow to red foliage. This tree has a variety of uses. The sweet sap can be collected in the spring — it is less concentrated than the sap of sugar maples, and is used primarily as a drink. The leaves have been used as packing material for apples and root crops, and leaf extracts exhibit antibacterial activity. The dense wood has been used as a fuel.

Sweetgum Flowers (Liquidambar styraciflua)

As you walk the Arboretum trails in early April, especially along the Old Kerr Hollow Road, you are likely to encounter large numbers of brown, spiky Sweetgum fruits (brown, ball-shaped “gumballs”) on the ground. These fruits are shed as the flowers develop in the spring. If you encounter a low branch, you may see upright clusters of male flowers, usually subtended by a single long stalk with a cluster of female flowers. The stigmas of the female (pistillate) flowers cover the surface of the cluster. The male (staminate) flowers develop as a number of spherical heads (approximately 12 or more) along an upright axis. After pollination, the male clusters fall to the ground, and the tightly compact cluster of pistillate flowers develops into a spiky multiple fruit containing about 60 seed capsules. The light weight seeds are dispersed by wind, and the empty brown heads may remain on the tree throughout the winter. Birds and small mammals eat the seeds. Sweetgum is found in much of the Eastern U.S. south of New England, as well as south into Mexico and Central America. Additional information on Sweetgum is provided on our December Featured Plants web page.

Autumn Olive (Elaeagnus umbellata)

In mid-April Autumn Olive is in full bloom. As you walk the Cemetery Ridge Trail, you may notice the distinctive smell of its fragrant, pale white to yellow, tubular flowers. Autumn Olive is a deciduous, alternate-leaved shrub that may grow as high as 20 ft. It’s distinctive oblong leaves are dark green above and are covered with silvery scales beneath. The fruits turn red (dotted with silvery scales) in the early fall and are eaten by a variety of birds and small mammals. A native of China and Japan, it was introduced into North America in the 1830’s. It has been used as an ornamental and for strip-mine reclamation, windbreaks, and wildlife habitat. This shrub is an invasive species in Tennessee and is listed in the Severe Threat category by the Tennessee Exotic Pest Plant Council. The UT Forest Resources Center, in cooperation with UT faculty, is presently engaged in the testing of new herbicides to help eradicate Autumn Olive and other invasive, non-native plants.

Umbrella Magnolia (Magnolia tripetala)

Umbrella Magnolia is one of several native deciduous magnolias found in our area. A fairly large tree is found next to Scarborough Creek just to the northwest of the Arboretum entrance. Other examples can be seen along Old Kerr Hollow Road and the Tulip Poplar Trail. The large leaves (up to 24 in. long) are widest near the tips, narrowing to the base - two similar species in our region, Fraser Magnolia (M. fraseri) and Big Leaf Magnolia (M. macrophylla), differ in having earlike lobed leaf bases. The common name reflects the arrangement of its leaves clustered at the tips of the branches, resembling an umbrella. The large flowers, pale yellow to creamy white, are pollinated by beetles. Umbrella Magnolia is found throughout the Appalachians and Blue Ridge Mountains from Pennsylvania south to Georgia and Alabama, and west to Arkansas and Mississippi. It frequently occurs in mesic habitats such as along streams and creeks.

Oak Flowers (Quercus species)

During the second week of April, the pollen count is high, and major contributors include a variety of oak trees. Oaks have separate male and female flowers that develop on the same tree. The male catkins (aments), which have been described as looking like fuzzy worms dangling from the tree's branches, appear just as the leaves start to emerge and shed their pollen somewhat later. The small female flowers are inconspicuous and develop at the base of the emerging leaves, resembling leaf buds. Under magnification, one can see three styles at the tip of each pistil. Once pollinated, acorns develop over a period of two years for red oaks and one year for white oaks. The abundance of acorns produced (i.e., the amount of mast) can be greatly affected by weather conditions at the time of pollination. Freezing temperatures and/or rain at this critical time can have adverse effects on pollination, reducing this important food source for wildlife. A good discussion of acorn development can be found in the UT Extension publication W126. The Links menu at left, provides access to the UT Agricultural and Extension publications.

Beech Leaves (Fagus grandifolia)

Visitors to the Arboretum often ask "What is that tree with brown leaves on it all winter long?" The answer is the Beech tree, which is conspicuous along our trails with its golden-brown leaves of fall gradually becoming a duller brown as the winter progresses. In the spring, these leaves drop as the spear-shaped buds expand.

Mayapple (Podophyllum peltatum)

Mid to Late April

Mayapple is found throughout the Arboretum in small to large patches. It is especially conspicuous along the Oak-Hickory Trail, parts of the Cemetery Ridge Trail, and the Backwoods Trail at this time of year. Flowers will begin opening in mid-April.

Look for plants with two palmate leaves – the white flowers are found at the base of the petioles (stalks) of the two leaves. The pulpy fruit (the "apple") develops as the spring progresses and is the basis for the common name Mayapple. Although the leaves and roots are poisonous, extracts from the roots have been used for a variety of medicinal purposes such as treating jaundice, constipation, and hepatitis. A derivative from this plant has been approved for treatment of some cancers.

Trillium (Trillium species)

Late March to Early April

There are at least three species of Trillium present at the Arboretum: 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 color with the former having maroon to bronze colored flowers and the latter yellow flowers. These plants can be seen along many of the Arboretum trails, especially 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.

An 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.

Silverbell (Halesia tetraptera)

Mid to Late April

Silverbell can be seen in several locations at the Arboretum just below the Visitors Center near Scarborough Creek, along the lower Heath Cove Trail, and near the Program Shelter. It is a tree that is most typical of the southeastern mountains, but forms can be found throughout the southeastern and central U.S. Silverbell is in bloom this week and is readily recognized by its showy white, bell-shaped flowers hanging down from the branches. In late summer and fall, the green to brown, papery, 4-winged fruit has a long spike-like projection at its bottom.

A research collection near the Program Shelter was established in 1997 to evaluate ornamental characteristics, hardiness, and growth rate of trees obtained from 4 geographical areas in Tennessee, North Carolina, Arkansas, and West Virginia. Silverbells wood is valued for making furniture and wood carvings. Several cultivars have been developed for landscaping.

Pawpaw (Asimina triloba)

Mid to Late April

A planting of Pawpaws below the Program shelter began blooming in early April. Colonies of Pawpaw are also found along several trails, but these rarely bloom. Pawpaw is the northernmost member of the subtropical and tropical plant family Annonaceae. The bell-shaped flowers have six brown to purple petals. The stamens and pistils are borne on a raised receptacle. The flowers have a fetid smell that attracts beetles and flies as pollinators.

The large, fleshy, edible fruit (up to 16 cm long) matures in September and October and has been described as having a taste similar to a mixture of banana, mango and pineapple. Pawpaws are eaten raw or processed into deserts such as pies and ice cream, though they may cause stomach trouble for some people. They are eaten by a variety of wildlife. Recent research indicates Pawpaw has potential as an anti-cancer drug and as a pesticide. It is found throughout the Eastern U.S., except in New England, and as far west as Nebraska.

Princess Tree (Paulownia tomentosa)

Princess Tree (or Empress Tree) is a native plant of China that was introduced into the U.S. in the mid 1800’s. It can be found on Arboretum property, but is more commonly seen along roadsides and disturbed sites throughout our region. Although still planted as an ornamental tree and used for reclamation of mine sites, it is considered an invasive species in many states, including Tennessee. A member of the Figwort family (Scrophulariaceae), Princess Tree has bright upright clusters of violet flowers that are conspicuous at this time of year. The large leaves are oval to heart-shaped. The abundant seeds, borne in dry, brown capsules, are dispersed in the fall.

The tree can reproduce by seed and root sprout and grows very rapidly (as much as 15 ft per year). Once established it is difficult to eliminate. The UT Forest Resources Center, in cooperation with UT faculty, is presently engaged in the testing of new herbicides to help eradicate Paulownia and other invasive, non-native plants.

Tulip Poplar (Liriodendron tulipifera)

Late April to Early May

Tulip Poplar (or Yellow Poplar) is the state tree of Tennessee and is found throughout the Arboretum, where it is a prominent member of the deciduous forest replacing shortleaf and Virginia pines. Tulip Poplar is recognized by its tall straight trunks, its tulip-shaped flowers, and its distinctive leaves.

Because the yellow-green, tulip-shaped, upright flowers are found high in the tree canopy, they are often difficult to see. Look for yellow to cream flower parts on the ground beneath the trees; then look up to see the flowers. Tulip Poplar belongs to the Magnolia Family - two other native members of this family are found in the Arboretum forests - Cucumber Magnolia (Magnolia acuminata) and Umbrella Magnolia (M. tripetala). Look for these native species as you walk the Arboretum trails.

Little Brown Jug (Hexastylis arifolia var. ruthii)

Late April - Early May

Little Brown Jug is a perennial, evergreen wildflower that can be seen along many of the Arboretum's trails. Its unusual urn-shaped (or jug-shaped) flower is found at ground level, usually covered by leaves and other forest litter. The shiny, arrowhead-shaped leaves and glabrous flowers arise from an underground stem (rhizome). The sepals are fused into an urn-shaped, brown to reddish brown calyx tube (there are no petals) with pointed tips at the top. Within the urn are 12 stamens and a superior or partly inferior ovary having 6 styles.

Little Brown Jug belongs to the same plant family (Aristolochiacease) as Wild Ginger ( Asarum canadense), which has pubescent, heart-shaped leaves and a calyx tube that terminates in spreading or reflexed tips. The rhizome of both plants has an odor similar to ginger (as do the crushed leaves) and was used as a substitute for that spice by early settlers. Flowers of Little Brown Jug are pollinated by beetles and other insects in the leaf litter. Little Brown Jug is found throughout the Southeast. Native Americans used it for treating such ailments as stomach pains, whooping cough, heart problems, and asthma.

Crossvine (Bignonia capreolata)

Late April - Early May

Crossvine is one of three members of the Bignoniaceae plant family found in our area the other two being Catalpa (the bean tree) and Trumpet Creeper (Campsis radicans), both of which flower later in the year. Crossvine is in full bloom the last week of April and the first week of May. It is especially conspicuous on trees near Scarborough Creek along Old Kerr Hollow Road and in several places along the Cemetery Ridge Trail. It can also be seen driving along the Pellissippi Parkway as one approaches the Arboretum from Oak Ridge.

Crossvine can grow to more than 50 ft in length. Its compound leaves have three leaflets, the terminal one modified into tendrils that enable it to climb. These leaf characteristics differentiate it from Trumpet Creeper which has many leaflets, no terminal tendrils, but aerial rootlets for climbing. Crossvine has orange-red flowers while those of Trumpet Creeper are red. The tubular flowers of both Crossvine and Trumpet Creeper attract hummingbirds at different times of the growing season. Crossvine derives its common name from the fact that the pith of a cut stem often appears as a dark, cross-like center.

Ninebark (Physocarpus oblongifolia)

Late April - Early May

Ninebark is a native shrub found along streams, rocky banks and bluffs, and other sunny, mesic environments. It is found from southern Canada south to Florida, and west to Oklahoma and Kansas. Several individuals are growing in the UTAS wildflower garden next to the Arboretum Visitors Center. In 2010, a number of Ninebark plants were used in landscaping the new Arboretum parking lot. A member of the Rosaceae plant family, Ninebark has dense clusters of fragrant white flowers. As the fruits develop, the clusters turn pink and eventually a buff color. The alternate, 3-5 palmately lobed leaves are medium to dark green on the upper surface and somewhat lighter below. The dark brown to orange bark that peels into several layers is the basis for the common name Ninebark. The flowers provide an excellent source of nectar for a wide variety of insects, the fruits are eaten by birds, and deer may browse the foliage.

Fly Poison (Amianthium muscitoxicum)

Late April thru June

Fly Poison (also known as Stagger Grass) is a member of the Lily Family and is conspicuous from April through June. It has grass-like basal leaves and at full bloom a spectacular cylindrical, white inflorescence. Although the distribution of Fly Poison is reported to be throughout the Southeast, extending as far west as Oklahoma and as far north as New York, it is found infrequently in a range of habitats from wetlands to pine-oak forests. At the Arboretum, if can be see along the Oak-Hickory and Backwoods trails.

All parts of the plant are toxic, especially the bulb. In the past, a mixture of sugar or honey and crushed portions of the bulb was used to kill flies. Cattle and sheep may eat the plant when other forage plants are not available. The toxic alkaloid contained in the plants can cause the animals to stagger around before dying - thus the origin of the common name "Stagger Grass."

Rue Anemone (Thalictrum thalictroides)

Redbud (Cercis canadensis)

Flowering Dogwood (Cornus florida)

Purpleblow Maple (Acer truncatum)

Sweetgum Flowers (Liquidambar styraciflua)

Autumn Olive (Elaeagnus umbellata)

Umbrella Magnolia (Magnolia tripetala)

Oak Flowers (Quercus species)

Beech Leaves (Fagus grandifolia)

Mayapple (Podophyllum peltatum)

Trillium (Trillium species)

Silverbell (Halesia tetraptera)

Pawpaw (Asimina triloba)

Princess Tree (Paulownia tomentosa)

Tulip Poplar (Liriodendron tulipifera)

Little Brown Jug (Hexastylis arifolia var. ruthii)

Crossvine (Bignonia capreolata)

Ninebark (Physocarpus oblongifolia)

Fly Poison (Amianthium muscitoxicum)