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 (Faxus 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.

Pawpaw (Asimina triloba)

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.

Winged Sumac
(Rhus copallinum)

Winged Sumac (R. copallinum) is one of two common species of sumac found in our area. It has large pinnately compound leaves with petioles that have “wings” - flattened blade-like structures - running along the leaf stalk between the leaflets. The flowers appear in June, and the dull red to purple fruits are well-developed by September. The leaves turn bright red in the fall.

Tulip Poplar (Liriodendron tulipifera)

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.

American Hornbeam (Carpinus caroliniana)

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.

Southern Red Oak (Quercus falcata)

Southern Red Oak is one of several red oak species at the Arboretum. The red oaks have sharply lobed leaves that are bristle-tipped and their acorns require 2 years to mature. Other common native red oaks occurring here include Black Oak (Q. velutina), Scarlet Oak (Q. coccinea), Northern Red Oak (Q. rubra), and Blackjack Oak (Q. marilandica). Red oaks differ from white oaks in having rounded leaf lobes or teeth without bristle tips and acorns that require only 1 year to mature. Southern Red Oak has distinctive alternate leaves which are shiny on the upper surface and rusty colored pubescent on the underside. Leaves on mature trees are deeply divided with long, sharply pointed lobed tips and 2-4 curved side lobes that are bristle-tipped. The leaf base tends to be rounded and resembles a turkey foot. Young trees may have bell-shaped leaves with 3-5 rounded bristle-tipped lobes. These leaves often resemble those of Blackjack Oak.

The dark bark has scaly ridges separated by deep narrow furrows. The acorns are orange-brown at maturity and their caps cover 1/3 or less of the nut. The acorns are important food for wildlife, and the wood is used as lumber for many purposes.

A closely related species, Cherrybark Oak (Q. pagoda) has been considered a variety of Scarlet Oak, but it is now recognized as a separate species. It is typically found along coastal plains in the Eastern U.S., while Scarlet Oak occurs on drier upland sites throughout the Southeast.

Flowering Dogwood (Cornus florida)

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.

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

White Oak (Quercus alba)

White Oak, a dominant tree of the eastern deciduous forest, is found along many of the Arboretum trails and in the Oak Collection near the Program Shelter. It grows to heights of 100 ft, with a canopy spread that may be 50-80 ft wide. Its light green leaves have 7-9 rounded lobes and are from 4-7 in. long. White Oak ranges from Maine and adjacent Canada south to northern Florida, Georgia, and Alabama, and west to Minnesota and Texas. White Oak provides important food and cover for many birds and mammals. An important lumber tree, it is used for furniture, whiskey barrel staves, and many other purposes.

The broadly oval buds are reddish brown and have no pubescence. Large crops of acorns are produced periodically - a single tree may produce 10,000 to over 20,000 acorns. The acorns have shallow caps that are smooth underneath. They do not exhibit dormancy but germinate shortly after they fall to the ground with the root penetrating the soil in the fall, but the shoot not developing until the following spring.

The light-gray bark is typically divided into long broad scaly plates or ridges. On large trees the bark is often broken into scaly broad plates and smooth patches may be evident.

White Oaks (Quercus spp.)

Several types of white oaks are producing abundant acorns this year. The acorn production (mast) from these oaks provides an important food for such animals as deer, squirrels, turkeys, and bears. The acorns of white oaks need 1 year to mature; red oaks require 2 years. White oaks have lobed leaves or ones with rounded teeth, while red oaks generally have sharp-lobed, bristle-tipped leaves. For general information about oaks, read "On the Prowl for Oaks", a Tree Fact article written by Richard Evans, UT Arboretum Director.

White Oak (Q. alba) is one of the most common oaks found along Arboretum trails. Its acorns, which occur in clusters of two or three, are often green when they first fall but at maturity are a rich brown.

Chestnut Oak (Q. montana) is also common along our trails and is especially conspicuous along the Lost Chestnut Trail. The large (up to 1 1/2 in.) acorns have a thin, warty cap and are shiny and brown to black at maturity.

Scattered individuals of Post Oak (Q. stellata) are found at the Arboretum. Typical leaves are broader at the top and often resemble a cross. The relatively small acorns (up to 3/4 inch long) are covered for 1/3 to 1/2 their length by a bowl-shaped cup.

The range of Bur Oak (Q. macrocarpa) extends into northwestern Tennessee, but is centered in the Midwest. Several individuals are found in the Oak Collection near the Program Shelter. Bur Oak has broad spatulate leaves and produces large acorns (up to 2 inches long) with a distinctive fringed cup.

Scarlet Oak
(Quercus coccinea)

At the end of October, the peak of fall colors is waning, and leaves are accumulating on the forest floor. The leaves of Scarlet Oak, one of the most colorful contributors to this fall display, turn bright red before falling. You can see this tree along our Arboretum trails. It is a member of the red oak group, with its sharply lobed, bristle-tipped leaves and deep, C-shaped sinuses extending close to the mid-vein — features distinguishing it from northern red oak and black oak. The swollen bases of many older trunks is caused by the same fungus that causes chestnut blight. Scarlet Oak ranges from New England, south along the Appalachians and Piedmont to Alabama and Georgia, and west to Michigan, Illinois, Missouri and Mississippi. The wood is used as lumber, flooring, and furniture. Its acorns are favorite food for deer, small mammals, and birds.

Hickories (Carya spp.)

A variety of hickories occur in the Arboretum forests. Identifying a tree as a hickory is relatively easy - it has alternate, compound leaves (several leaf blades associated with each axillary bud) with 5 to 9 leaflets. Identifying the species of hickory, however, is more challenging and often requires determining characteristics of the leaves, hickory fruits (outer husks and nuts), the terminal buds, and the bark. Furthermore, there is considerable variation of these characteristics within a species and hybridization of species produces individuals with intermediate or mixed characteristics. Three of the more common hickories found at the Arboretum are described below. For more information about hickories in general, read "Hickory Hunt", a Tree Fact article written by Richard Evans, UT Arboretum Director.

Pignut Hickory (C. glabra) leaves typically have 5 to 7 glabrous leaflets (i.e. without hairs). The pear-shaped to ovoid fruits are about 1 inch in diameter, with thin husks and nuts that are not ribbed. The bark is relatively tight, has vertically oriented ridges that are rounded, and may be flaky.

Mockernut Hickory (C. tomentosa) has leaves with 7 to 9 leaflets that are pubescent on the undersides. The globular to oval fruits are about 1 1/4 inches in diameter, with thick husks and a 4-ribbed nut. The tight bark has flat to rounded, interlaced ridges.

A few Shagbark Hickories (C. ovata) are found along our trails. Their leaves usually have 5 essentially glabrous leaflets. The 1 1/2 inch diameter fruit has a thick, rounded husk that splits all the way to the base, and a nut ridged on 4 sides. The distinctive bark is broken into long, shaggy plates.

Ginkgo (Ginkgo biloba)

Ginkgo (or Maidenhair Tree) is putting on its spectacular fall display. For a short period its leaves turn bright yellow, and then almost overnight they fall to the ground creating a conspicuous leaf shadow under the tree's spreading branches. A well-developed Ginkgo can be seen across the Arboretum entrance road from the Visitors' Center. Several Ginkgos can also be seen in the Shade Tree Study Area near the Program Shelter.

Ginkgo is a Gymnosperm — its developing ovules and seeds are not enclosed in an ovary. Its fan-shaped leaves resemble those of Maidenhair Fern (hence its common name) and have dichotomous (forked) venation. Ginkgo is well-represented in the fossil record. For thousands of years it only survived in temple gardens in China. The tree is often referred to as a living fossil. Ginkgo is dioecious with separate male and female trees. The male trees are most commonly planted because the female trees produce fruits with a strong, malodorous odor. Ginkgos are hardy trees that are planted in many parts of the U.S. and elsewhere.

Sourwood (Oxydendrum arboreum)

A small to medium-sized tree, Sourwood is found along many Arboretum trails. As a member of the Ericaceae Family, it is related to such plants as blueberries, rhododendrons, and azaleas. The white, bell-shaped flowers are borne in terminal one-sided clusters and become conspicuous in June. The fruits persist on the flower stalks often into the fall and winter. Because the flowers are often near the top of the trees, they may be difficult to see under a forest canopy. A good place to observe these trees in bloom is in a study plot of Sourwood just below the Elmore Holly Collection.

The ridged and often deeply furrowed bark of Sourwood is readily identified especially in older trees where it becomes blocky. In the fall, the leaves turn bright red. The tree’s common name comes from the sour taste of the leaves and twigs. Leaves and bark of Sourwood were used by Native Americans and early settlers to treat a variety of ailments such as mouth ulcers, asthma, indigestion, and kidney and bladder ailments. Sourwood honey is a favorite of many.

American Beech (Fagus grandifolia)

American Beech is a common tree found at the Arboretum. It is identified by its smooth gray bark; alternate, serrate leaves with straight, parallel veins, each ending at a tooth on the leaf margin; and elongate, pointed buds on the twigs. The yellow (turning to brown) leaves in the fall persist throughout the winter. A large beech tree is found along Marsh Road, on the left just past the Magnolia Orchard.

The tree flowers in April. Developing beechnuts can be seen now on the Marsh Road tree. When mature in the fall, the spiny fruit husk (bur) contains two (sometimes three) nuts, which are eaten by many birds and mammals. Beech wood is used for many purposes, such as flooring, furniture, plywood, railroad ties, and firewood. Beech mast is not produced every year but rather at intervals of 2 to 8 years.

Blackjack Oak (Quercus marilandica)

Blackjack Oak is one of the less common oaks along Arboretum trails. Scattered individuals can be seen along Marsh Road and elsewhere on drier sites. Its presence most likely indicates past clearing for crops and/or a history of fire. Blackjack Oak may invade disturbed sites along with Shortleaf and Virginia Pine and can remain a component of the maturing deciduous forest for many years. Its distinctive leathery leaves are broadest at the tip with 3-5 bristle-tipped, rounded lobes. The lower leaf surface is velvety and rusty brown, while the upper surface is a shiny dark green.

The bark is thick, blocky, and dark, almost black. It is found throughout the eastern US — south from New York and the Midwestern states and west to Oklahoma, Texas, Kansas, and Missouri. It is a major component of the Cross Timbers bordering the plains at the western edge of its distribution, and it is also an important constituent of the Pine Barrens in New Jersey. The wood has been used to make charcoal, railroad cross-ties, and fuel.

Sassafras (Sassafras albidum)

Sassafras, a tree frequently seen along Arboretum trails, has distinctive leaves varying from a common 3-lobed shape, to a mitten shape, to an elliptical or oval unlobed leaf. This year its small greenish-yellow flowers came out in early April before the leaves. In October, the orange, red, to almost pink leaves contribute to a brilliant display of fall colors. The dark blue fruits (drupes) can be seen in September before they are quickly consumed by birds.

Sassafras is widely distributed in the Eastern and Midwestern US, ranging south from southern Maine and Michigan (and southern Ontario), and west to Iowa, Illinois, Missouri, Kansas, Oklahoma, and Texas. It can grow to heights of 60-70 ft— in the Arboretum forests, it is most commonly a member of the understory and lower canopy where it is often found growing in clonal clumps. It is an early invader of disturbed areas and can often be seen along forest edges.

Sassafras has been used for a variety of medicinal purposes. The roots and bark have been used for making Sassafras tea and root beer flavoring, and ground-up leaves are used to make Filè powder, a food thickening agent used in Cajun cooking. Safrole, a carcinogenic component of sassafras oil, has been banned for use as a flavoring by the US Food and Drug Administration.

Red Maple (Acer rubrum)

Red Maple is found on a wide variety of sites throughout the Arboretum’s forests. Its fall foliage presents a brilliant display of color from bright yellow and orange to red. The opposite, palmate leaves are mostly 3-lobed but sometimes have 5 lobes. In the summer, the leaf petioles (leaf stalks) are often red and the undersides of the leaves are pale green to silver. In spring, red maple is one of the earliest trees to bloom (as early as February or March). Its small red flowers produce abundant seeds that are eaten by squirrels, birds, and other wildlife.

Red maple is found throughout the Eastern U.S. and Midwest — from the Maritimes in Canada and New England, to Florida, and west to Texas and Minnesota and states in-between. A number of excellent cultivars are available that are among the most popular landscaping tree species available.

Sweetgum (Liquidambar styraciflua)

Sweetgum is a deciduous tree that holds onto its leaves late into the fall. In December one can still find occasional trees with a few yellow to purple leaves along with conspicuous stalked, spiny fruits hanging from the branches. At the Arboretum, Sweetgum is most commonly found along the Old Kerr Hollow Road in a relatively moist habitat.

Sweetgum is found in much of the Eastern U.S. south of New England. The fruits consist of seed pods united into dense spiny balls. The bark is deeply furrowed into narrow ridges, and the twigs often develop corky ridges along their length. The lobed leaves, which resemble maple, have a pungent odor when crushed. The gum from which Sweetgum derives its common name has been used since before the 16th century for incense, perfumery and medicinal purposes. Sweetgum lumber has a variety of uses such as furniture, crates, cabinets, and barrels, and its distinctive heartwood is often referred to as "red gum" lumber. It is also an important shade tree.

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