Adam's Needle (Yucca filamentosa)

Several Yucca plants can be seen along the North Forest Loop Road, the new Rock Pile Lead trail, and elsewhere on the Arboretum. These plants are known as Adam's Needle, Bear Grass, or Spanish Bayonet and most likely represent ones that were planted at or escaped from old home sites. They have sword-like pointed leaves (8-32 in. long) that radiate upward from very short woody stems at the ground surface. The margins of these fibrous leaves fray into stiff, filamentous, white threads that curl along the leaf edges. In summer Yucca produces a tall stalk (3-8 ft high) with showy, creamy white flowers. Yucca depends on a moth for pollination, while the moth requires the Yucca as a site for raising its larvae - a classical example of mutualism. The female Yucca moth collects pollen balls from the anthers of a Yucca flower which she then transfers to another flower. At the same time she deposits one or more fertilized eggs into the plant's ovule. As the moth larva develops, it feeds upon the Yucca seeds.

Yucca belongs to the plant family Agavaceae (though some botanists assign it to the Liliaceae). There are 40-50 members of this genus, many growing in arid desert to semi-desert climates. The UT Herbarium web page lists two species of Yucca present in our area - Yucca filamentosa and Y. flaccida - both commonly called Adam's Needle. Some botanists consider these both to be Yucca filamentosa. These species were most likely originally found along coastal areas of the Southeast but have become naturalized inland to the west and north.

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Alders (Alnus spp.)

As spring approaches, two species of alder along Scarboro Creek below the Visitors Center come into bloom. The conspicuous male catkins which first appear in the late fall only shed their pollen in late January and early February. The pistils of the female cones emerge with warmer days.

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.

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Black Alder (Alnus glutinosa)

European Black Alder, a native species of Europe, western Asia, and northern Africa, is also known as Common Alder or Black Alder. It has been widely planted in the U.S. and has become naturalized in the Northeast, the Midwest, and Maritime Canada. As with other species of alder, European Black Alder does well on wet sites such as stream banks and wetland situations, but it can also grow on drier sites where the soils are infertile. It is used for reclamation of strip mines because it can grow rapidly to help control erosion, and its nitrogen-fixing root nodules and abundant leaf litter improve soil fertility. It provides cover and a dependable food source for seed-eating birds during the winter.

The leaves readily distinguish it from other alders in being rounded to obovate - the sticky leaves and twigs are the basis for the specific name "glutinosa."

A European Black Alder in the Arboretum's Marsh Area has been listed as a Tennessee State Champion Tree based on its girth, height, and crown.

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Allegheny Chinkapin (Castanea pumila)

Allegheny Chickapin is a shrub or small tree found in the foothills of East Tennessee and on the Cumberland Plateau. Its range extends from Pennsylvania, Ohio, and New Jersey, south to Florida, and west to Texas and Oklahoma. It is closely related to American Chestnut (Castanea dentata) and Chinese Chestnut (Castanea mollissima). The species has a number of varieties, some populations of which are susceptible to Chestnut Blight, which eliminated American Chestnut as one of the dominant trees of the eastern deciduous forest. Other Chinkapin populations are at least somewhat resistant to this disease. Allegheny Chinkapin may grow as high as 65 ft, but typically it is a shrub only growing to heights of 30 ft or less. Its oblong leaves have fine to coarse, bristle-tipped teeth along their margins and are densely pubescent underneath. The shrub produces showy unisexual male catkins that are as long or longer than the leaves. Shorter bisexual catkins bear female flowers at their base and male flowers along the rest of the axis. The fruits, consisting of bristly husks (burs), contain 1-3 nuts and are considered by some to be tastier than the American Chestnut. They are a prime food for a variety of wildlife.

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American Holly (Ilex opaca)

American Holly is found as an understory tree in a variety of habitats throughout the Arboretum. Although it can grow to heights of 50-60 feet, most of the trees along our trails are much smaller, reflecting their slow growth rate and the relatively recent disturbance history of our forests. After the leaves have fallen, these trees become more readily visible with their spiny, evergreen leaves.

American Holly belongs to a large genus of more than 400 different species found around the world. The range of this species extends from southern New England to Florida, and west to eastern Texas and southern Missouri. A row of large American Holly cultivars was planted along Valley Drive in the mid-1960's when the Arboretum was first established. Some other American Holly cultivars can be seen in the Harold Elmore Holly Garden.

American Holly is distinguished by its simple, leathery, evergreen, spine-tipped leaves and its light gray bark. It is dioecious, bearing male and female flowers on separate plants. The small greenish-white flowers appear in late spring, and the red fruits mature on the female plants in late fall and persist into the winter. The fruits (4-seeded drupes) are collected along with the leaves for Christmas wreaths and other holiday decorations. The fruits are eaten by birds and small mammals, but can be toxic to humans and pets. The wood is suitable for inlays in cabinet work, handles, carvings, rulers, and scientific instruments. When dyed black to resemble ebony, the wood is used for violin pegs, piano keys, and fingerboards.

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Amur Honeysuckle (Lonicera maackii)

One of the more troublesome invasive plants in our area is Amur Honeysuckle, a tall shrub (up to15-20 ft high) forming dense thickets that inhibit the growth of native plants. A native of central and eastern Asia, it was brought to North America as an ornamental in the late 1800's. It is an aggressive invader of edge habitats such as fence rows, the understory of secondary forests, and other previously disturbed areas. Amur Honeysuckle's ability to outcompete native species is associated with several characteristics: one of the first plants to leaf out in the spring and last to lose its leaves in the fall; its production of abundant seeds that are widely dispersed by birds and germinate readily; an aggressive growth rate; and its formation of dense shrubby thickets that shade out native understory plants. Research suggests that predation of nests is higher in Amur Honeysuckle than for native shrubs, and the nutritional value of its fruits for migrating birds is less than that of native plants.

Its simple, opposite leaves are medium to dark green and up to 3.5 in. long, with long tapering tips. The white tubular, two-lipped, fragrant flowers appear in April and turn yellow with age, similar to those of Japanese Honeysuckle. The clusters of abundant, dark red, spherical fruits (berries) become conspicuous in September and persist into the winter months. Amur Honeysuckle is multi-trunked and shallow rooted. It has been used as an ornamental, for hedges and screens, and to attract wildlife. It is found in 24 states in the eastern and central U.S., and in our state is listed as a "Significant Threat" by the Tennessee Exotic Pest Pant Council.

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American Beautyberry (Callicarpa americana)

American Beautyberry is a native shrub found in the Southeastern US from Maryland to Florida, and west to Oklahoma and Texas. An excellent specimen of this plant can be seen in front of the Arboretum's Visitors Center. The pink flowers develop along the stem at the leaf nodes in early August. After pollination, the fruits develop as dense ball-like clusters of green drupes. These mature later in the fall into conspicuous purple fruits that may persist well into the winter months. The fruits provide a source of food for a variety of birds.

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American Witch Hazel (Hamamelis virginiana)

The American Witch Hazel found next to Scarboro Creek below the Visitors Center blooms in late January. It is distinguished at this time of year by four yellow, strapped-shaped, crumpled petals that first appear early in the month. This tall shrub to small tree is found on a variety of habitats in many parts of middle and east Tennessee. It has forked branches, and its leaves resemble American Hazelnut (Corylus americana). The open, dried, capsule-like fruits can be seen on the flowering branches. Its fragrant foliage, twigs, and bark produce an extract that has been used as an astringent and toiletry. Its fruit is eaten by a variety of birds and other wildlife. Two individuals of a related species, Vernal Witch Hazel (Hamamelis vernalis), are also present next to the Creek. Their reddish to purplish flowers emerge toward the end of January.

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Amur Cork Tree (Phellodendron amurense)

Amur Cork Tree, a native of eastern Asia, was introduced into the eastern U.S. in the mid-1800's. Since then It has been widely planted as an ornamental and street tree. Over time it has become naturalized, spreading into forests where it can outcompete native deciduous species such as oaks and hickories.

Amur Cork Tree is considered an invasive species in a number of states. Two specimens of Amur Cork Tree were planted in the Arboretum's Shade Tree Collection in 1966. Numerous seedlings and saplings are found throughout the Arboretum and are removed along the trails as time and resources permit.

Amur Cork Tree is dioecious - individuals have either male or female flowers. Small yellow/green flowers appear in late spring and develop into abundant small black fruits (drupes) with large numbers of seeds that are dispersed by birds. In China, Japan, and India, the bark has been used for medicinal purposes. The yellow inner bark is used as a dye. "Wood turners" use the lightweight, yellow-colored wood to make decorative vases and pots. Since the wood is rot resistant, it has also been used for railings and erosion control structures.

Its common and scientific names refer to the thick, deeply fissured, corky bark. It grows to heights of 30 to 50 ft, with massive, widely spreading branches, and it has opposite, pinnately compound, dark green leaves with 5 to 13 leaflets.

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Arborvitae
(Thuja occidentalis and Platycladus orientalis))

Arborvitae, a popular landscape tree, is represented by several plantings in the Arboretum's Conifer Collection. The name Arborvitae is derived from Latin meaning "Tree of Life." References indicate it has been associated with long life and vitality in China, and early North American explorers used the foliage as a source of Vitamin C to treat scurvy. Northern White Cedar (Thuja occidentalis) is native to the Northeast and North Central U.S. and adjacent Canada, extending south along the Appalachians to Kentucky, Tennessee, and North Carolina.

One well developed cultivar in the Conifer Collection is Elegantissima Arborvitae (Thuja occidentalis 'Elegantissima') found at the edge of the Juniper Garden. This is one of the more commonly planted cultivars. The scale-like leaves are overlapping and tightly appressed to the twigs. In winter the leaves turn yellowish-green but become darker green during the growing season.

A second cultivar, Pyramidal Arborvitae, Thuja occidentalis 'Pyramidalis,' grows to heights of 20 to 30 ft. It has a narrow, pyramidal to conical form. The flattened branches are sprays of bright green scale-like leaves. For both these cultivars, the inner-most leaves turn brown in the winter, fall to the ground, and form a thick litter mat at the base of the tree.

Chinese (or Oriental) Arborvitae, Platycladus orientalis, was considered a species of Thuja until recently, but is now placed in a separate genus. It is native to Northwestern China and Korea but has become naturalized in many parts of Asia. It may grow to heights of 50 ft. and has ascending branches arranged in flat, vertical planes. The triangular, scale-like leaves are tightly packed and overlapping.

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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.

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Siebold Ash (Fraxinus sieboldiana)

An attractive tree in the Shade Tree Collection is Siebold Ash, a native of China, South Korea, and Japan. It is a relatively small tree growing to heights of 20-30 ft. Siebold Ash is one of the few ash species that has fragrant, showy flowers with a corolla composed of linear white to cream petals. It bears both bisexual (perfect) and unisexual (imperfect) flowers in the spring. A member of the Olive Family (Oleaceae), Siebold Ash is one of about 65 species in the genus Fraxinus. As with other ash species, this tree has opposite, pinnately compound leaves with 5-7 leaflets. The dark green leaves turn an attractive red/purple in the fall. The fruit (a samara - a simple dry, winged fruit) matures in the fall and is tinged with purple. The wood is used in Asia to make high quality furniture and wood utensils.

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