Description and habitat

Eastern Flowering Dogwood (Cornus florida) is one of North America’s most showy Dogwood species, featured on the Norfolk County’s coat-of-arms and flag (often viewed flying in small towns, such as St. Williams). Each May, the branches are smothered with beautiful white-petaled flowers, measuring up to 3 cm long. In fact, these petals are the leaf bracts (modified leaves) surrounding the true flower. Flowering Dogwood leaves are oppositely arranged (as in most dogwoods), and simple, up to 9 cm in length and 6 cm in width, oval with entire margins. The foliage turns into a gorgeous red in the autumn. The bark, dark grey in colour, is comprised of square plates on mature trees.  The fruits of flowering dogwood are in the form of a red 1 cm long drupe, occurring in clusters of around 8-12 fruits. They are highly valued by wildlife – readily consumed by frugivorous birds, as well as small mammals.

The Eastern Flowering Dogwood is one of 9 species of Dogwood commonly found in Ontario. The other species are Alternate-leaved (Pagoda) Dogwood (Cornus alternifolia), Grey Dogwood (Cornus racemosa), Silky Dogwood (Cornus amomum), Roughleaf Dogwood (Cornus drummondii), Round-leaved Dogwood (Cornus rugosa), Blue-fruited Dogwood (Cornus obliqua), Red-osier Dogwood (Cornus sericea), and Bunchberry (Cornus canadensis). All of these species except for Bunchberry are deciduous shrubs, while Bunchberry grows has a short, spreading form like an herbaceous wildflower. Also in the Dogwood Family (Cornaceae) is Black Gum (Nyssa sylvatica), a common tree species within deciduous swamps. Flowering Dogwoods are widely distributed across Eastern North America, extending south into the Florida panhandle. In Canada, substantial populations are found within the Long Point Basin, and the Skunk’s Misery area of southwest Middlesex County.

Flowering Dogwoods are mostly found in moist and wet forests, growing alongside other deciduous shrubs such as Witch Hazel (Hamamelis virginiana) and American Hornbeam (Carpinus caroliniana). They can be found in both Sugar Maple (Acer saccharum) – Beech (Fagus grandifolia) associations, and Red Maple (Acer rubrum) – oak (Quercus sp.) communities – the latter ecosystem is where they are mostly observed. They are moderately shade tolerant, and fire sensitive. Flowering Dogwoods are also intolerant of flooding; thus, they are typically absent from swamps with standing water.

Wildlife importance 

The bright red berries that appear in autumn are rich in fat and calcium, making them a crucial food source for over 30 species of birds, especially songbirds like American Robins (Turdus migratorius), Eastern Bluebirds (Sialia sialis), Red-eyed Vireos (Vireo olivaceus), Warbling Vireos (Vireo gilvus), and Cedar Waxwings (Bombycilla cedrorum), as well as game birds like Wild Turkeys (Meleagris gallopavo) and grouse (Tetraonidae), helping them build up fat reserves for winter or migration. Various small mammals such as squirrels (Sciuridae) and Eastern Chipmunks (Tamias striatus) also readily consume the berries. The leaves are an important for the insect community, especially as a larval food source for lepidopterans (butterflies and moths), such as Spring Azure (Celastrina ladon), and the Dogwood Thyatirid (Euthyatira pudens).

Dogwood Anthracnose

The Dogwood Anthracnose Fungus (Discula destructiva) currently threatens Flowering Dogwood populations. This disease produces brown blotches on dogwood leaves, and cankers on the bark. If the cankers reach the main stem, the dogwood tree will experience dieback, sometimes leading to morality.  Dogwood Anthracnose can be spread by wind, rain, and wildlife, such as insects and birds. Currently, there is no effective control at the population level for dogwood anthracnose. Disease resistance rates are around 10-20%, with much local variation. While this does suggest a substantial population decline in heavily infected areas, Flowering Dogwood will continue to be part of Ontario’s natural landscape in the long-term. Some cultivars with high anthracnose resistance rates have been developed for horticultural purposes.

Fun facts

• The timing of the Flowering Dogwood bloom is closely associated with temperature – and can be significantly delayed during cool springs!
• The autumn foliage colour of dogwood – while typically red, can vary widely from bright orange to a deep burgundy!
• Flowering Dogwoods often exhibit a characteristic horizontal branching pattern (like Pagoda Dogwoods), creating a layered or tiered appearance to their crown. This unique structure can make them easily recognizable, even in the absence of flowers or fruit.
• In addition Dogwood Anthracnose – a relatively novel threat, Flowering Dogwoods can also be impacted by other diseases, including powdery mildew, leaf spot diseases, and various borers. These diseases are naturally occurring, allowing Flowering Dogwood to adapt to these threats over time; so they aren’t usually a severe threat to the species.
• There are well over 100 different cultivars of Flowering Dogwood utilized for horticultural purposes. These include weeping cultivars, along with those with pink or yellow flower colour!

 

Written by Matthew Palarchio, HBSc in Environmental Sciences, Western University.

Photo Credits (L-R)
Autumn leaves © Matthew Palarchio
Bark © Matthew Palarchio
Summer foliage © Matthew Palarchio
Flower © Reuven Martin

 

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