The University of Tennessee - Forest Resources Research and Education Center

'Winterberry' (Ilex verticillata) is one of several deciduous hollies present in the Arboretum’s Marsh Area. These are part of the Elmore Holly Collection which is described in detail - including a full list of the collection and a site map.

Although one usually thinks of hollies as being evergreen, a variety of hollies lose their leaves each fall and provide a display of bright colored fruits at this time of year. 'Winterberry' is one of three native deciduous hollies found in East Tennessee - the others being Carolina Holly (Ilex ambigua v. amigua) and Mountain Holly (Ilex ambigua v. montana). Many culivars and hybrids using Winterberry have been developed including the four examples shown below that can be seen in the Marsh Area this winter.

Left: 'Winter Gold' (Ilex verticillata)
Right: 'Bonfire' (Ilex serrata x verticillata)
'Stop Light' Holly

Left: 'Stop Light' (Ilex verticillata)
Right: 'Earlibright' (Ilex verticillata)

Tigertail Spruce (Picea polita or Picea torano)

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.

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.

Virginia Pine (Pinus virginiana)

Early to Mid February

Virginia Pine (also known as Scrub Pine) is one of the more common native pines found at the Arboretum. Its twisted, yellowish-green needles are borne in bundles of two, a characteristic that helps distinguish it from Shortleaf Pine which has straight needles in bundles of 2-3. Trunks of older Virginia Pine retain many dead limb stubs below the canopy. The flaky bark is light brownish orange to gray-brown. The seed cones, which require 2 years to mature, have scales with thickened ends bearing slender, stiff prickles. Pollen cones develop in the spring and produce copious amounts of pollen.

Virginia pine, which may grow up to 70 ft in height, is a pioneer species that becomes established in open areas created by fire or other disturbance. The presence of older Virginia Pines in the Arboretum’s deciduous forest reflects a history of forest development on abandoned farmlands. Research at UT on Virginia Pine has included studies of genetic and environmental variability that influence tree growth and productivity.

Alders (Alnus spp.)

As spring approaches, two species of alder along Scarboro Creek below the Visitors Center have come into bloom. The conspicuous male catkins first appeared late this fall, but only now are shedding pollen. The pistils of the female cones have just emerged during the warm weather of the last weeks.

The Seaside Alder (Alnus maritima) has an unusual distribution, being found on the Delmar Peninsula of Maryland and Delaware, in northern Georgia, and in Oklahoma. Recent studies suggest these disjunct (isolated) populations, left behind as the glaciers receded, have become distinct subspecies.

Our native Hazel Alder (Alnus serrulata) ranges throughout the Eastern U.S. and west to Indiana, Missouri, Oklahoma and Texas. The fruits are found as clusters of cone-like structures that remain attached to the shrub throughout the winter.

Alders are generally associated with habitats such as stream banks, pond edges, and other wetlands. These shrubs are among a group of woody plants that have root nodules with symbiotic nitrogen-fixing bacteria. These bacteria convert inorganic nitrogen from the atmosphere to a form that can be used by plants. Studies have shown that the increased availability of nitrogen from alders can result in increased growth of trees planted in the same stands. Such studies support the idea that this nitrogen-fixing association enables alders to invade disturbed areas deficient in nitrogen.

Cilician Fir (Abies cilicica)

The Dwarf and Unusual Conifer collection adjacent to Valley Drive has a number of interesting conifers from other parts of the world. One of these, Cilician Fir, is a native of Turkey, Lebanon, and Syria. Its name reflects the geographic region from which it comes. The Plains of Cilicia extend along the Mediterranean coast of Turkey north and northeast of the Island of Cyprus and adjacent to the Taurus Mountain. A narrow gorge through the mountain range is known as the Cilician Gates and provides access to the Anatolia Plateau. This gorge has served as a major military and commercial route for centuries.

In its native habitat Cilician Fir is a component of degraded forests at higher elevations (3200 to 7200 ft). The tree has a conical shape and may reach heights of 100 ft.

It has been used as a diuretic and to treat wrinkles, extract worms, and promote hair growth. Cilician Fir has been used for a variety of other purposes such as lumber, masts for boats, flag poles, and joinery.

Its grayish-brown bark is covered with resin pockets. The flat, evergreen needles, 1 to 1.5 in. long, are shiny green above, and underneath have two white bands formed by several lines of stomata. The upright cylindrical cones have resinous scales. The resin from these cone scales has been collected and used in mummification and in folk medicine as an antiseptic, for treating bacterial and viral infections, and for its anti-inflammatory, and antipyretic properties.

Boxwoods (Buxus spp.)

Although Boxwoods are native to parts of Europe, northern Africa, the Mediterranean region, and Asia, they have been used in North America for landscaping since colonial times. There are an estimated 70 to 80 species of boxwood, two of which - Buxus sempervirens (Common Boxwood) and B. microphylla (Littleleaf Boxwood) - have been used extensively to develop many hybrids and cultivars. Boxwoods are evergreen shrubs with opposite leaves that produce small yellow-green male and female flowers in the late spring or early summer. Although the flowers are not conspicuous, they are quite fragrant and attractive to bees. Because Boxwoods respond well to pruning, they are used for hedges, foundation plantings, topiary gardens, bonsai, and many other landscaping purposes. Most boxwood plants used for landscaping are small to large shrubs, but species such as Common Boxwood can grow to heights of 20 ft or more if not subjected to pruning. The wood from such plants is very hard and heavy and has historically been used for cabinet making (hence the name boxwood), engraving blocks for printing, handles for tools and daggers, and parts of musical instruments. A planting of 20 different boxwood hybrids and cultivars adjacent to the Arboretum’s Program Shelter is being evaluated by UT researchers.

Korean White Pine (Pinus koraiensis)

A large Korean White Pine tree highlights part of the Arboretum’s conifer collection across from the Program Shelter and adjacent to the oak collection. This native of NE Korea, Japan, Manchuria, and eastern Russia is found in mountain forests. It is similar to our native White Pine (Pinus strobus) in having 5 needles (2-5 in. long) per bundle, and elongate cones (3.5-6 in. long) borne on short peduncles (stalks).

The gray to gray-brown bark is broken into irregular oblong plates. This tree is referred to as the Korean Nut Pine because the seeds are edible and can be eaten raw or cooked as a staple food. They are also used for flavoring and as a thickener. The seeds have been used medicinally for their analgesic, antibacterial, and anti-inflammatory properties, and the turpentine obtained from the tree has been used for a wide variety of treatments. This tree is considered good for bonsai.

Yellow Twig Dogwood (Cornus sericea 'Midwinter Fire')

A bright spot of color in the Wildflower Garden at the Arboretum Visitors Center this month is a Yellow Twig Dogwood. This is a cultivar of Redosier Dogwood (Cornus sericea, also known as Cornus stolonifera), a northern species that is not native to Tennessee. While Redosier Dogwood is noted for its bright red to dark red stems and vegetative reproduction from stolons, several cultivars have been developed that have different colored stems. One of these, 'Midwinter Fire', is characterized by stems that are a combination of yellow, red, and orange. The leaves are similar to our Flowering Dogwood, and the small flowers are borne in flat-topped cymes. The colorful stems that become apparent during the winter months make this a desirable plant for landscaping. Cutting the stems back each year promotes the continued development of the brightly colored stems.

Cornelian Cherry Dogwood (Cornus mas)

Late February to Early March

A major research collection of Cornelian Cherry Dogwood cultivars is present along Arboretum Drive and behind the Juniper Garden and Conifer Collection. Cornelian Cherry Dogwood is a multi-stemmed, small tree or shrub native to Central and Southern Europe and Western Asia. The fruit, which matures in summer, is bright red and olive-shaped. In its native habitat the fruit is used for syrup and jams. This Dogwood is one of the earliest flowering trees at the Arboretum - the first blooms were evident in the collection this past week (February 17). The numerous, small yellow clusters of flowers appear before the leaves. The objective of the ongoing research study is to identify plants with exceptional ornamental value (flowering, fruiting, and form) that are hearty in this climate. The seeds for the collection were obtained from native trees in Rumania and Croatia.

Leatherleaf Mahonia (Mahonia bealei)

February - March

Leatherleaf Mahonia (also known as Beale’s Mahonia) is a native of China that has been planted extensively and is a potential invader of Southeastern woodlands. This upright, evergreen shrub produces terminal clusters of fragrant yellow flowers near the end of February into early March. At the Arboretum, it is found along parts of the Tulip Poplar and Heath Cove trails, among other places, and is frequently observed under forest canopies and along forest edges in the Oak Ridge area. It has dark green, alternate pinnately compound leaves with sharp, spiny leaflets somewhat resembling holly leaves. This upright shrub produces grape-like clusters of bluish-gray fruits in early summer which are attractive to birds - a related species Mahonia aquifolium with similar fruit is known as Oregon Grape. The Tennessee Exotic Pest Plant Council lists Mahonia bealei in its “Alert” category because of its invasive characteristics.

Deciduous Hollies

Tigertail Spruce (Picea polita or Picea torano)

Virginia Pine (Pinus virginiana)

Alders (Alnus spp.)

Cilician Fir (Abies cilicica)

Boxwoods (Buxus spp.)

Korean White Pine (Pinus koraiensis)

Yellow Twig Dogwood (Cornus sericea 'Midwinter Fire')

Cornelian Cherry Dogwood (Cornus mas)

Leatherleaf Mahonia (Mahonia bealei)