Dogwoods are very popular ornamental plants used in a variety of landscapes. The many cultivars of dogwoods beautifully display a wide range of color in their bracts, foliage and twigs during various seasons of the year. Most tree species generally grow up to a height of 20 - 30 feet and require little maintenance (Powell, 1997).
Possibly the most popular dogwood in the United States is the flowering dogwood, Cornus florida. It represents the state flower of North Carolina and Virginia, the state tree of Missouri and Virginia, and is designated as the 'State Memorial Tree' in New Jersey. Its popularity is also demonstrated in the economic value it brings to the dogwood industry of Tennessee, which is an estimated $30 million annually (Bir, 2001).
Dogwoods used for landscape purposes are sometimes classified according to the season in which their display is most attractive (Bir, 2001). For example, Cornus alba (the Tartarian dogwood) and C. sericea (the Redosier dogwood) are considered winter dogwoods, which are generally grown for their colorful stems. Variation of stem color ranges from creamy yellow, orange and shades of red to deep red. Their flowers also attract an assortment of butterflies during their flowering period. Cornus florida and C. kousa (the oriental dogwood) are considered spring dogwoods, which display an attractive range of colorful bracts and foliage depending on the cultivar during the spring season.
Cornus florida, C. kousa, and C. nuttallii (the Pacific dogwood) are three of the most widely cultivated dogwoods in the United States. Over 100 cultivars have been described for C. florida, with variations of color and size observed in bracts and leaves, along with various patterns of branching (Santamour and McArdle, 1985). The natural range of C. florida extends east of the Mississippi River from Maine to northern Alabama. Some popular cultivars of C. florida include: 'Bonnie'- large blooms (4.5 to 6 inches across); 'Cherokee Chief '- red bracts; 'Green glow'- large dark green leaves, with a golden vein in leaves ; 'Purple Glory'- purple leaves; dark red bracts.; 'Pygmy' - dwarf tree size, white bracts; 'World's Fair'- white bracts, large diameter limbs, drought resistant; 'Pendula' or 'Weeping'- upright central shoot, with pendulous or weeping side branches.
Cornus kousa is a native of eastern Asia. It is a smaller tree with white or pink bracts and dark green foliage late in the spring season. Blooms generally appear after the foliage, as opposed to before as seen in C. florida. Some of the more popular cultivars of C. kousa include: 'Greensleeves,' 'Milky Way,' 'Blue Shadow'- white bracts; 'Rosabellla,' 'Rubra,' 'Rosea'- pink bracts. The fruits are red and compound, in contrast to those in C. florida and C. nuttallii, which have distinct fruits in clusters. Fruits of C. kousa are edible and sweet, and have been used in wine making.
Cornus nuttallii, which naturally grows in western North America from California to British Columbia, has six showy bracts, rather than only four as seen in C. florida. The number of known cultivars are much fewer in number than found in either C. florida or C. kousa (Santamour and McArdle, 1985). However, it is still valued as an ornamental dogwood due to its large, showy bracts. Due to the rapid spread of plant diseases such as dogwood anthracnose (see Pathology of Cornus), research is underway to improve propagation techniques that could rapidly propagate plants with resistance to the disease. Edson et al. (1994) found that shoot tips from Cornus nuttallii could be micropropagated in vitro on nutrient rich media, then rooted ex vitro more easily and rapidly than traditional methods, allowing for a faster propagation of plants for research.
Natural hybridization between some blue- or white-fruited dogwood species is relatively common. Interspecific hybrids such as C. amomum x C. racemosa (C. x arnoldiana Rehder) and C. rugosa x C. stolonifera (C. x slavinii) are frequently found in Michigan and neighboring states (Wagner, 1990). A recently described natural hybrid between C. racemosa (the gray dogwood) and C. rugosa (the round-leaved dogwood) was described by Wagner (1990) from Michigan. Almost all of the morphological characters of this hybrid, named C. x friedlanderi, are intermediate between the parents, making it appear similar to C. amomum.
Additional examples of natural hybridization have been documented in various arboreta or botanical gardens. The opportunity for hybridization is sometimes increased in arboreta, where several closely related species may grow in close proximity. An example of this in Cornus is a hybrid between C. obliqua and C. racemosa (C. x arnoldiana), which was reported in 1903 by Alfred Rehder from the Arnold Arboretum. Although this hybrid was originally reported from cultivation, it was later found in natural populations from New England to Missouri (Kehne, 1978). Another hybrid, C. dubia, was described by Rehder growing in the Arnold Arboretum in 1923, which was a cross between C. paucinervis and C. amomum. Redher described two other Cornus hybrids from cultivation including C. x horseyi, a hybrid between C. macrophylla and C. amomum, and C. x dunbarii, a hybrid between C. macrophylla and C. asperifolia. These hybridization events could only occur naturally in a garden or arboretum or through an artificial cross since C. amomum and C. asperifolia are native to eastern North America, and C. macrophylla is native to Asia.
Natural hybridization frequently causes confusion in the taxonomic treatment of the taxa involved. For example, intermediate morphological characteristics resulting from hybridization between C. stolonifera and C. occidentalis led to the designation of several species, subspecies, and varieties in this species complex in North America (Rickett 1944). Cornus baileyi and C. interior were recognized as distinct species within this species complex, but later treated as formae of C. stolonifera (Rickett 1944).
Artificial hybrid cultivars have also been produced using Cornus species for horticultural purposes. One of the most popular hybrid cultivars, 'Eddie's White Wonder,' is a hybrid between C. florida and C. nuttallii. This hybrid combines the attractive flower structure of six bracts as in C. nuttallii with the autumn foliage coloration as seen in C. florida.
In 1965, Elwin Orton of Rutgers University experimented with crossings between C. florida, C. nuttallii, and C. kousa. He was successful in crossing C. florida and C. kousa and produced six cultivars known as Stellar Hybrid Cultivars, which include 'Aurora,' 'Constellation,' 'Celestial,' 'Stardust,' 'Stellar Pink,' and 'Ruth Ellen' (Orton, 1965). These hybrids begin to bloom in April just as the parental C. florida blooms are beginning to fade. In general the Stellar hybrid cultivars have large white or pink blooms and show some resistance to dogwood diseases such as dogwood anthracnose and mildew.
Two artificial hybrid cultivars between C. capitata and C. kousa ('Porlock' and 'Norman Hadden' are also used as ornamental plants (Hillier and Coombes 2002). Both the 'Norman Hadden' and 'Porlock' cultivars grow into a small tree with white bracts in June that turn to a deep pink in July. Fruits of 'Porlock' are red and compound as seen in C. kousa.
Ethnobotany encompasses the "understanding of the classification, uses, and practical, religious, and superstitious concepts concerning plants in primitive or unlettered societies" (Alcorn, 1995). People have studied and classified plant species according to their many medicinal, nutritious, and practical attributes for many centuries. As early as 77 AD, the Greek surgeon Dioscorides wrote De Materia Medica, a collection of detailed descriptions and uses for 600 plants found in the Mediterranean region. In 1753, Carolus Linnaeus recorded almost 6000 plants from Europe, and his students traveled the globe in search of new plants and their uses (Holmstedt, 1995).
Native Americans have long benefited from the inherent qualities from over 5000 plants used as drugs, foods, fibers and dyes among other uses in North America (Moerman, 1998). Included are at least 14 species and several varieties of Cornus. For example, tree bark from C. alternifolia and C. florida have been chewed to release analgesic compounds to treat headaches, toothaches, and other pains. Cornus canadensis (dwarf or bunchberry dogwood) has anti-convulsive, anti-fever and analgesic properties among others that have been used to treat a number of ailments. Other species have been used to treat ailments of the kidney (C. rugosa), stomach (C. racemosa), throat (C. foemina) and lungs (C. amomum). In a rank of the top 10 plants with the most number of uses by Native Americans, Cornus sericea, ranked fifth with almost 200 total uses (Moerman, 1998).
In addition to medicinal value, Native Americans found other uses for Cornus species. For instance, wood from C. florida is used in wood carvings for decorative purposes. Other examples include wood for making tools (C. amomum), fiber for basket making (C. glabrata), dyes made from bark (C. nuttallii; C. sericea), and fruits used for food (C. canadensis; C. suecica; C. sericea). The inner bark of several trees including C. alternifolia and C. amomum is sometimes mixed with tobacco leaves for smoking.
Dogwood species in China have also been widely explored for their ethnobotanical uses. For instance, the fruits of the cornelian cherry, C. officinalis, are known as "Zhu Yu" or "Zao Pi" in Chinese medicine and prescribed as an astringent tonic for impotence, spermatorrhea, lumbago, vertigo, night sweats. Fruits of C. oblonga have been used as a substitute for 'Zao Pi.' Seeds of several Chinese species including C. oblonga, C. alba, C. hemsleyi, C. walteri, and C. wilsoniana contain oils that are used commercially. The bark from C. oblonga and C. capitata are also used medicinally as folk remedies to treat arthritis and injuries. The fruits of several subspecies of C. hongkongensis are edible and used for wine brewing, and the hard wood is used in building.
For more details and descriptions of Chinese dogwood species, please refer to ‘Taxonomic Treatment of Chinese Species.’
David T. Thomas
Department of Botany
NC State University
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