Black Oak (Quercus velutina)
Black Oak is a common and important tree in the deciduous forests of our area, as reflected in the name of the ridge on which the City of Oak Ridge is built. Its range extends throughout much of the Eastern and Midwestern US. Black Oak leaves are quite variable and often difficult to differentiate from other members of the red oak group, such as Northern Red Oak. The leaves are from 4-10 in. long with 7-9 bristle-tipped lobes. Their upper surface is shiny green, while the lower is a paler green. Shade leaves have relatively shallow lobes, while sun leaves are more deeply lobed. As fall progresses, the leaves turn yellow to bronze and then red. Seeds mature over a two-year period, germinating in the spring after they fall. Seeds are an important food for wildlife such as squirrels, deer, and turkey.
The smooth, gray bark of young trees becomes dark gray to black with deep furrows as it matures. The grayish pubescent terminal buds tend to be square in cross section. The inner bark is orange to yellow in color ("pumpkin" color), which is a diagnostic feature for identifying Black Oak. A scaly cap covers 1/3 to 1/2 of the brown acorn at maturity.
Although the seeds contain bitter tannins, these can be leached with water. The powdered acorns have been used as a thickening for stews and as a flour. Acorns have also been roasted as a substitute for coffee. The dense wood is used for furniture, flooring, railroad ties, rough lumber, and fuel.
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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.
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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.
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Oriental Bittersweet (Celastrus orbiculatus)
A walk along Cemetery Ridge Trail during our first snowstorm of the year (December 5, 2009) highlighted the bright red fruits of the Oriental Bittersweet vines that climb and, in some cases, cover some of the trees and shrubs along the trail. The fruits are initially green, but become bright yellow at maturity. When the yellow capsule breaks open in the fall, it reveals a fleshy red aril which contains two brown seeds.
The small greenish flowers develop in the spring (at the end of April this year). Each flower is typically unisexual either male or female, but some perfect flowers occasionally develop. The leaves are rounded to acute/elliptic, the latter shape being more common at the end of young developing shoots.
This invasive woody vine was introduced to the US in the mid- to late 1800s and is especially troublesome in New England, the Atlantic coastal states, and the southern Appalachians. The vine aggressively twines around tree and shrub stems and can strangle (by girdling) or completely covers and shades out its hosts. The fruits are eaten and spread by birds. People also inadvertently help spread the attractive fruits which they gather for holiday decorations. Such decorations should be destroyed completely after the holidays to limit the spread of this invasive plant. At the Arboretum, Oriental Bittersweet is most common in relatively open areas along forest edges and is one of several invasive plants the Arboretum staff is attempting to eradicate.
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Oxeye Daisy (Leucanthemum vulgare)
Populations of Oxeye Daisy are conspicuous near the upper end of Old Kerr Hollow Road, along Arboretum Drive, and along other trails at the Arboretum in early summer. The showy white flower with a bright yellow center was introduced from Europe in the 1800s and has spread throughout much of North America. Oxeye Daisy produces abundant seed, which remains viable for up to 6 years. It also spreads by vigorous vegetative reproduction of its root system. This invasive plant is listed as a noxious weed in at least five western states and in Ohio. The Tennessee Exotic Pest Plant Council lists Oxeye Daisy as a Rank 3 species (exotic plant species that spread in or near disturbed areas and are not considered a threat to native plant communities.)
Oxeye Daisy is typically found in fields, waste places and other disturbed sites, as well as in the partial shade of open-canopy forests and along forest edges. The individual flower heads, which may be up to 2 inches in diameter, consist of sterile white ray flowers surrounding the yellow disk flowers in the center. Oxeye Daisy has been used for a variety of medicinal purposes and for making wines and tonics.
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