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COSEWIC Assessment and Status Report on the Eastern Flowering Dogwood in Canada

COSEWIC Status Report
on the
Eastern Flowering Dogwood
Cornus florida
in Canada
2007

Species Information

Name and Classification

Cornus florida L., commonly known as eastern flowering dogwood or flowering dogwood (French: Cornouiller fleuri), has only one synonym and it is not in current use: Cynoxylonfloridum (L.) Raf. ex B.D. Jackson. The genus is in the dogwood family (Cornaceae).


Morphological Description

A small tree of the forest understory or edge 3-10 m high; branches are in whorls from the main trunk, giving a tiered appearance. Bark on larger specimens is grey-brown and separates into quadrangular plates, forming an alligator skin pattern. Each branch is composed of a sequence of annual growth segments originating from a sub-terminal position, resulting in a conspicuous scalloped appearance. Leaves are simple, opposite and deciduous. Blades are ovate, elliptic to broadly oval, 5-15 cm long and 2.5-8 cm wide. Flowers are in terminal clusters with four conspicuous white floral bracts, appearing in mid-spring as the leaves are just beginning to develop (Figure 1). The floral buds are stalked, large and have a flattened dome shape. Fruits are scarlet, shiny, one-seeded, ovoid and fleshy and occur in tight clusters. The species is similar to alternate-leaved dogwood (Cornus alternifolia), but the latter has alternate leaves and branching and lacks the floral bracts; the fruits are dark green to blue in an open cluster.


Genetic Description

There are no conspicuous barriers to gene flow within populations; flowers are perfect and self incompatibility occurs with some but not all self-pollinations (Reed, 2004). Craddock et al. (1997) found that 3 of 7 cultivars of this species would not set fruit with self-pollination but did with most cross-pollinations. Sork et al. (2002) estimated 8-11 effective pollen donors for Cornus florida trees in Missouri forests. Fruit commonly is present on trees that have flowered. Habitat fragmentation has resulted in moderate geographic barriers between some populations. Little is known of population differences other than some observations on geographic differences, for example, fruit weights tend to decrease with decreasing latitude and increasing length of growing season (Winstead et al., 1977); however, the trend reverses in Mexico, where Cornus florida var. urbaniana, a variety found in the mountains of Nuevo León and Veracruz, differs from the typical species by its greyer twigs and larger fruit (Vimmerstedt, 1965).


Designatable Units

A single designatable unit is here recognized for this widespread eastern North American species.


Figure 1: Leafy Branchlet of Cornus florida with a Terminal Flower Cluster of Tiny Flowers Surrounded by Four, Large, White, Petal-like Bracts (centre) and a Longitudinal Section of a Single, Enlarged, Flower (left)

Figure 1: Leafy branchlet of Cornus florida with a terminal flower cluster of tiny flowers surrounded by four, large, white, petal-like bracts (centre) and a longitudinal section of a single, enlarged, flower (left)

Illustration from Britton and Brown (1913).