There is always something in bloom at the Arboretum! Use our Plants Library to plan a photo shoot, to choose one of the trails to walk, or learn more about the plants at the Arboretum.
Mistletoe (Phoradendron leucarpum)
Clumps of Mistletoe resembling large green squirrel nests become conspicuous in the upper branches of deciduous trees after the leaves have fallen. Sprigs of its green leathery leaves and stems and its white berries are a familiar component of the Christmas time tradition of kissing under the Mistletoe. In ancient times it was used by Druid and pre-Christian traditions to decorate houses at the mid-winter and mid-summer solstices. In our area, Mistletoe is found on such trees as oaks, hickories, red maples, and sweetgums.
Although not commonly found at the Arboretum, Mistletoe is frequently seen in Oak Ridge, Clinton, and along the Pellissippi Parkway. It is considered to be semi-parasitic because its modified roots penetrate the bark and vascular tissues of the host tree and access water and minerals for the developing plant, but it does not appear to harm the host. In the winter, Mistletoe clumps consist of a heavily branched system of greenish stems bearing opposite, leathery, leaves containing chlorophyll. While these clumps are heavily shaded by the host tree's canopy during the summer, they are well adapted to photosynthesize after leaf fall - it has even been suggested that they may contribute food to the host tree during the winter months.
Mistletoe bears inconspicuous yellow flowers and white, translucent berries. Birds disperse the seeds in their droppings and by wiping sticky residues of the fruits adhering to their beaks onto other trees. Phoradendron leucarpum occurs throughout much of the eastern US from New Jersey to Florida and as far west as Texas and Illinois. Species of Mistletoe in the western US are parasitic on conifers and can be a significant problem.
European 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 many areas of eastern North America. In 2003 a European Black Alder in the Arboretum's Marsh Area was listed as a Tennessee State Champion Tree based on its girth, height, and crown. This tree subsequently died and has been removed.
European Black Alder is used for reclamation of strip mines because it grows rapidly and helps control erosion. 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. Alder wood has been used for timber, as fiber for paper and particle board, in joinery as solid wood or veneer, and for fuel wood.
The glossy, dark green leaves of European Black Alder are broadly ovate to obovate (broadest above the middle) in shape. The sticky leaves and twigs give rise to the species name "glutinosa." The male catkins form in the fall and persist during the winter. The female catkins develop in late winter, and the inconspicuous flowers bloom before leaf emergence. Woody cones develop during the summer with seeds being dispersed in the fall. The cones persist throughout the winter months. 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.
Hollies (Ilex species)
Hollies are found throughout the world occupying a wide range of habitats. More than 780 native evergreen hollies and 30 native deciduous hollies are recognized. Although North America is not considered a major center of holly diversity, it does have 23 native hollies, with 7 present in Tennessee. Many holly cultivars have been developed and are used extensively in landscaping. Hollies have a rich history of medicinal uses, as religious symbols, and in superstitions. They are also used widely in holiday decorations. An excellent discussion of the history, use, and taxonomy of hollies can be found in Fred C. Galle's book Hollies: The Genus Ilex, Timber Press, Portland, Oregon 1997.
The Harold L. Elmore Holly Collection at the UT Arboretum contains over 200 evergreen and deciduous Holly cultivars and is recognized by the Holly Society of America as an official collection of Hollies. As part of this collection, a variety of deciduous hollies have been planted in the Arboretum's Marsh Area. Other Holly plantings are found along Valley Drive and Shade Tree Lane. Our native American Holly (Ilex opaca) is present in the forest understory throughout the Arboretum and can be seen along many of our trails.
(From left: White Oak, Chestnut Oak, Blackjack Oak, Post Oak, Bur Oak)
An acorn is the fruit of an Oak tree - a single-seeded nut covered by a woody cap (cupule). These fruits contain tannins that are toxic in large amounts to most domestic animals, with the notable exception of pigs. Acorns, however, are an important food for deer, squirrels, turkeys, and other wildlife. When soaked to remove the tannins, acorns provided a food staple for Native Americans. They have also been used as a coffee substitute, when coffee was unavailable.
(From left: Black Oak, Southern Red Oak, Scarlet Oak, Sawtooth Oak, Shingle Oak)
A diversity of oaks can be found along our Arboretum trails and in the Oak Collection near the Program Shelter. Some of the more common acorns you might find at the Arboretum in the fall, illustrated above, have distinct characteristics that aid in identifying the species.
As late summer transitions into fall, hikers along the Arboretum's trails are likely to encounter numerous acorns, hickory nuts and other fall fruits. The quantity of these fruits, collectively referred to as mast, can vary strikingly from year to year. The term 'mast' comes from an ancient Anglo-Saxon word referring to nuts and fruits on the forest floor that provided food for hogs and other domesticated animals. Today the term is used more generally to refer to fruits produced by woody plants that provide food for wildlife.
A distinction is made between hard and soft mast. Hard mast consists of hard shelled fruits and seeds (e.g., acorns, hickory nuts, beechnuts, black walnuts, pine seeds) which are high in carbohydrates, fats, and proteins. Hard mast generally matures in the late summer and fall and may persist into winter months. It can provide an important source of food for wildlife when other food is scarce. Soft mast, on the other hand, refers to fleshy fruits (e.g., black cherries, blackberries, raspberries, muscadines, persimmons, serviceberries) having a high content of sugars, vitamins, and carbohydrates. Soft mass is usually unavailable during winter months, but it can play a role as a source of moisture for wildlife during dry periods and as a food source for migratory birds.
An intriguing aspect of hard mast, in particular, is the variability in the amount produced in any given year. While a number of theories have been advanced to explain this variability, none of the reasons for yearly fluctuations in mast production appear to be conclusive. Weather and local climate fluctuations, however, clearly play an important role. In high mast years, the abundant supply of available food in the fall and winter can contribute to wildlife survival and reproduction, while in lean years, wildlife may be forced to forage widely for food, and populations may decline.
Chinese Chestnut (Castanea mollissima)
A native of China and Korea, the Chinese Chestnut has been planted extensively in the US as an ornamental. It is resistant, but not immune, to the chestnut blight which virtually eliminated the American Chestnut (Castanea dentata) from the Eastern Deciduous Forest of North America. Chinese Chestnut cultivars are being crossed with American Chestnuts in a breeding program to develop a hybrid resistant to the chestnut blight.
At this time of year, the ground below two Chinese Chestnut trees upslope from the Arboretum Visitors Center is littered with large spiny chestnut fruits (burs), up to 3 in. long and over one inch in diameter, containing one to three shiny brown nuts. These edible nuts are flattened on one or two sides and very attractive to squirrels and other wildlife. Once they have fallen, they can pose a significant litter problem.
Chinese Chestnut is monoecious, bearing male and female flowers on long (4-5 in.), fragrant, yellowish-white catkins in June. As with other members of the genus Castanea, the male flowers make up the upper portion of the catkins, while a small number (1-3) of inconspicuous female flowers occur at the base. The undersides of the glossy toothed leaves (5-8 in. long) and the twigs are densely pubescent.
Chinese Chestnut can be distinguished from the native American Chestnut by the dense pubescence on its twigs and the undersides of its leaves (American Chestnut leaves and twigs are essentially glabrous) and the number of nuts in each bur - 2 to 3 versus 1 (rarely 2). In addition, the spiny bracts surrounding the nuts are larger for the Chinese Chestnut.
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No collecting of plant materials is permitted at the UT Arboretum.