Cornus florida

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Cornus florida
Flowering Dogwood in fall with fruit
Flowering Dogwood in fall with fruit
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Cornales
Family: Cornaceae
Genus: Cornus
Subgenus: Benthamidia
Species: C. florida
Binomial name
Cornus florida
L.

Cornus florida (Flowering Dogwood, syn. Benthamidia florida (L.) Spach) is a species of dogwood native to eastern North America, from southern Maine west to southern Ontario and eastern Kansas, and south to northern Florida and eastern Texas and also in Illinois, with a disjunct population in eastern Mexico in Nuevo León and Veracruz.

A single inflorescence, showing the large, white petal-like bracts and the tight cluster of small greenish-yellow flowers.
A single inflorescence, showing the large, white petal-like bracts and the tight cluster of small greenish-yellow flowers.

Flowering dogwood is a small deciduous tree growing to 10 m high, often wider than it is tall when mature, with a trunk diameter of up to 30 cm. The leaves are opposite, simple, oval with acute tips, 6-13 cm long and 4-6 cm broad, with an apparently entire margin (actually very finely toothed, under a lens); they turn a rich red-brown in fall.

The flowers are individually small and inconspicuous, with four greenish-yellow petals 4 mm long. Around 20 flowers are produced in a dense, rounded, umbel-shaped inflorescence, or flower-head, 1-2 cm in diameter. The flower-head is surrounded by four conspicuous large white, pink or red "petals" (actually bracts), each bract 3 cm long and 2.5 cm broad, rounded, and often with a distinct notch at the apex. The flowers are bisexual.

While most of the wild trees have white bracts, some selected cultivars of this tree also have pink bracts, some even almost a true red. They typically flower in early April in the southern part of their range, to late April or early May in northern and high altitude areas. The similar Kousa Dogwood (Cornus kousa), native to Asia, flowers about a month later.

Close up of a flower cluster showing the four yellow petals on each flower.
Close up of a flower cluster showing the four yellow petals on each flower.

The fruit is a cluster of two to ten drupes, each 10-15 mm long and about 8 mm wide, which ripen in the fall to a bright red, or occasionally yellow with a rosy blush. They are an important food source for dozens of species of birds, which then distribute the seeds.

There are two subspecies:

Contents

[edit] Ecology and disease

Flowering dogwood is very susceptible to dogwood anthracnose, a disease caused by the fungus Discula destructiva. This disease has killed many wild stocks, while domestic landscape plantings have been less affected because of better air circulation and less humid conditions, which discourage the fungus. The Kousa Dogwood is resistant to this disease, as is the C. florida cultivar ‘Appalachian Spring’.[1]

The other major disease of flowering dogwood is powdery mildew, caused by a fungal obligate biotrophic parasite, the most common species of which is Microsphaera pulchra. While powdery mildew does not generally kill the tree, it can stunt its growth, cause early leaf senescence, reduce the intensity of fall color, or otherwise damage its aesthetic value. It is generally controlled by applications of fungicides throughout the growing season, but current research is exploring the possibility of using different microorganisms as biological control agents. So far 10 species of filamentous fungi, 5 yeasts, and 10 bacteria have shown promise as biological control agents by reducing disease by up to 90%, but further work is needed to develop and test commercial formulations of these strains. [2] In the meantime, resistant cultivars such as 'Cherokee Brave', 'Jean's Appalachian Snow', 'Karen's Appalachian Blush' and 'Kay's Appalachian Mist' can be planted to avoid the problem.[3]

Flowering Dogwood leaves serve as foodplants for the caterpillars of some Lepidoptera, e.g. the Io moth (Automeris io).

[edit] Cultivation

Mature flowering dogwood bark showing dark gray blocky pattern.
Mature flowering dogwood bark showing dark gray blocky pattern.

Flowering Dogwood does best horticulturally in moist, acidic soil in a site with some afternoon shade, but good morning sun. It does not do well when exposed to intense heat sources such as adjacent parking lots or air conditioning compressors. It also has a low salinity tolerance. In urban and suburban settings, care should be taken not to inflict mower damage on the trunk or roots, as this increases the tree’s susceptibility to disease and pest pressure.[4]

In regions where dogwood anthracnose is a problem, homeowners and public land managers are encouraged to know the symptoms and inspect trees frequently. The selection of healthy, disease-free planting stock is essential and transplanting trees from the forest should be avoided. Sites should be selected for reasonably well-drained, fertile soils; full sun is recommended in high-hazard areas (such as stream or pond banks). New plantings should be mulched to a depth of 2-4 inches (5-13 cm), avoiding the stem. Dead wood and leaves should be pruned and completely removed and destroyed yearly. Plants should be watered weekly during droughts, with watering done in the morning, avoiding wetting the foliage. Registered fungicides can be applied when necessary, according to manufacturers instructions and advice of local Extension Service.[5]

Flowering dogwood is grown widely throughout mid-temperate North America. In the eastern part of the continent, it is cultivated as far north as Toronto and south to central Florida. Farther west, places of cultivation include Boulder, Sacramento and Vancouver. It is also sold in other temperate parts of the world, including Sydney, Australia.

Selected cultivars
  • ‘Amerika Touch-O-Pink’ – large bracts, tinged pink; large leaves; good disease resistance.
  • ‘Appalachian Spring’ – large white bracts; red fall foliage; resistant to dogwood anthracnose.
  • 'Autumn Gold' - white bracts; yellow fall color.
  • 'Barton' - large white bracts; blooms at early age; resistant to stem canker and powdery mildew.
  • 'Bay Beauty' - double white bracts; resists heat and drought; good for Deep South.
  • 'Cherokee Daybreak' - white bract; vigorous grower with variegated leaves.
  • 'Cherokee Chief' - red bracts; red new growth.
  • 'Cherokee Brave' - Even redder than 'Cherokee Chief', smaller bracts but dark red color; consistently resistant to powdery mildew.
  • 'Cherokee Princess' - vigorous white bracts, industry standard for white flowers.
  • 'Cherokee Sunset' - purplish-red bracts; variegated foliage.
  • 'Gulf Coast Pink' - best pink flowering dogwood in Florida.
  • 'Hohman's Gold' - white bracts; variegated foliage.
  • ‘Jean’s Appalachian Snow’ – large, overlapping white bracts w/ green flowers; very resistant to powdery mildew.
  • ‘Karen’s Appalachian Blush’ – delicate white bracts edged in pink; some powdery mildew resistance.
  • ‘Kay’s Appalachian Mist’ – stiff, creamy white bracts; red fall foliage; good resistance to powdery mildew.
  • 'Plena' - double white bracts; spot anthracnose-resistant.
  • 'Purple Glory' - red bracts; purple foliage; spot anthracnose-resistant but susceptible to stem canker.
  • 'Weaver White' - large white blooms; large leaves; candelabra shape; good in north-central Florida.

[edit] Propagation

Cornus florida is easily propagated by seeds, which are sown in the fall into prepared rows of sawdust or sand, and emerge in the spring. Germination rates for good clean seed should be near 100% if seed dormancy is first overcome by cold stratification treatments for 90 to 120 days at 4°C (40°F).[6][7]

Flowering dogwood demonstrates gametophytic self-incompatibility, meaning that the plants can’t self-fertilize. This is important for breeding programs as it means that it is not necessary to emasculate (remove the anthers from) C. florida flowers before making controlled cross-pollinations. These pollinations should be repeated every other day, as the flowers must be cross-pollinated within one or two days of opening for pollinations to be effective.[8]

Softwood cuttings taken in late spring or early summer from new growth can be rooted under mist if treated with 8,000 to 10,000 ppm indole-3-butyric acid (IBA). In cold climates, potted cuttings should be kept in heated cold frames or polyhouses the following winter to maintain temperatures between 0 and 7°C. Although rooting success can be as high as 50-85%, this technique is not commonly used by commercial growers. Rather, selected cultivars are generally propagated by T-budding in late summer or by whip grafting in the greenhouse in winter onto seedling rootstock.[9][10]

Micropropagation of flowering dogwood is now used in breeding programs aiming to incorporate resistance to dogwood anthracnose and powdery mildew into horticulturally and economically important cultivars. Nodal (axillary bud) sections are established in a culture of Woody Plant Medium (WPM) amended with 4.4 μM 6-Benzyladenine (BA) to promote shoot growth.[11] Rooting of up to 83% can be obtained when 5-7 week-old microshoots are then transferred to WPM amended with 4.9 μM IBA.[12]

[edit] Historical uses

Other old names now rarely used include American Dogwood, Florida Dogwood, Indian Arrowwood, Cornelian Tree, White Cornel, False Box, and False Boxwood. This species has in the past been used in the production of inks, scarlet dyes, and as a quinine substitute. The hard, dense wood has been used for products such as golf club heads, mallets, wooden rake teeth, tool handles, jeweler’s boxes and butcher’s blocks.[13][14]

[edit] References and external links

Wikimedia Commons has media related to:
Wikiversity
Wikiversity has bloom time data for Cornus florida on the Bloom Clock

A Flowering Dogwood cultivar with pink flowers

A Flowering Dogwood cultivar with white flowers

Tree shape, autumn

Sapling of C. florida 'Appalacian Spring'

Leaves of C. florida 'Appalacian Spring'

Leaf closeup of C. florida 'Appalacian Spring'

A pink-flowered C. florida.

White C. florida. 'Bay Beauty'. Note the double bracts.

[edit] References

  1. ^ Cappiello, P and D Shadow. 2005. Dogwoods: The Genus Cornus. Timber Press, Portland. 224 pp.
  2. ^ Mmbaga, MT, RJ Sauve, FA Mrema. 2007. Identification of microorganisms for biological control of powdery mildew in Cornus florida. Biological Control 44: 67-72.
  3. ^ Windham, MT, WT Witte, RN Trigiano. 2003. Three white-bracted cultivars of Cornus florida resistant to powdery mildew. HortScience 38(6): 1253-1255.
  4. ^ Cappiello, P and D Shadow. 2005. Dogwoods: The Genus Cornus. Timber Press, Portland. pp 98-100.
  5. ^ Anderson, RL, JL Knighten, M Windham, K Langdon, F Hendrix, R Roncadori. 1994. Dogwood anthracnose and its spread in the South. Project Report R8-PR 26. USDA Forest Service, Atlanta, GA. 10pp.
  6. ^ Cappiello, P and D Shadow. 2005. Dogwoods: The Genus Cornus. Timber Press, Portland. pp 100-102.
  7. ^ Hartmann, HT, DE Kester, FT Davies, RL Geneve. 2002. Hartmann and Kester’s Plant Propagation: Principles and Practices, 7th Edition. Prentice Hall, Upper Saddle River, NJ. pp. 769.
  8. ^ Reed, SM. 2004. Self-incompatibility in Cornus florida. HortScience 39(2): 335-338.
  9. ^ Cappiello, P and D Shadow. 2005. Dogwoods: The Genus Cornus. Timber Press, Portland. pp 102.
  10. ^ Hartmann, HT, DE Kester, FT Davies, RL Geneve. 2002. Hartmann and Kester’s Plant Propagation: Principles and Practices, 7th Edition. Prentice Hall, Upper Saddle River, NJ. pp. 769.
  11. ^ Kaveriappa, KM, LM Phillips, RN Trigiano. 1997. Micropropagation of flowering dogwood (Cornus florida) from seedlings. Plant Cell Reports 16: 485-489.
  12. ^ Sharma, AR, RN Trigiano, WT Witte, OJ Schwarz. 2005. In vitro adventitious rooting of Cornus florida microshoots. Scientia Horticulturae 103: 381-385.
  13. ^ Petrides, George A. 1972. A field guide to trees and shrubs; field marks of all trees, shrubs, and woody vines that grow wild in the northeastern and north-central United States and in southeastern and south-central Canada. The Peterson field guide series, 11. Boston: Houghton Mifflin. page 106.
  14. ^ Cappiello, P and D Shadow. 2005. Dogwoods: The Genus Cornus. Timber Press, Portland. pp 100.