The genus Cornus, commonly known as dogwood, encompasses a diverse group of plants that extends far beyond the single ornamental tree most people recognize. The total number of distinct dogwood species worldwide ranges from approximately 30 to 60, depending on botanical classification. While the showy, large-bracted flowering tree dominates public perception, the majority of dogwood species are actually smaller shrubs, trees with inconspicuous flowers, or even low-growing groundcovers.
The Scope of the Cornus Genus
The taxonomic structure of the dogwood family helps organize this diversity. Within the genus Cornus, botanists generally group species into four major categories that reflect shared characteristics: the Big-Bracted Dogwoods, the Cornelian Cherries, the Blue- or White-Fruited Dogwoods, and the Dwarf Dogwoods.
The Big-Bracted Dogwoods, such as the widely planted ornamental trees, are defined by their large, petal-like structures, which are actually modified leaves called bracts. The Cornelian Cherries are small trees or large shrubs that bloom very early with clusters of small, non-showy yellow flowers, later producing edible, cherry-like red fruits.
The largest group consists of the Blue- or White-Fruited Dogwoods, which are almost entirely shrubs and are often classified under the subgenus Swida. The Dwarf Dogwoods, belonging to the subgenus Chamaepericlymenum, are herbaceous perennial subshrubs rather than woody trees.
Defining the Major Flowering Tree Varieties
The most recognized members of the genus are the big-bracted species that grow into true trees, with three species dominating North America and Asia. The North American Flowering Dogwood (Cornus florida) is native to the eastern United States and typically matures into a small tree, reaching heights of 20 to 30 feet. This species is an early spring bloomer, and its four showy bracts are characteristically rounded with a distinct notch at the tip.
The Asian Kousa Dogwood (Cornus kousa), native to Japan, Korea, and China, is a later-blooming counterpart that grows up to 30 feet. The Kousa dogwood flowers several weeks later than its North American relative, and its four bracts are notably pointed at the tips, giving the bloom a sharper, star-like appearance. The fruit of the Kousa is distinctive, forming a large, fleshy, reddish drupe that resembles a raspberry.
The third major tree form is the Pacific Dogwood (Cornus nuttallii), native to the western coast of North America, which can reach 50 feet in height. Unlike the four-bracted eastern species, the Pacific Dogwood often produces six to eight large, white bracts around its central flower cluster. This species is less widely cultivated due to its lower tolerance for environmental stresses outside its native range.
Shrub and Groundcover Dogwood Species
The total species count is increased by numerous dogwoods that grow as shrubs or groundcovers, distinct from the flowering trees. The shrub dogwoods, such as the Red-osier Dogwood (Cornus sericea), are valued for their striking winter interest rather than their flowers. Their primary ornamental feature is the vibrant red or yellow color of their young stems, which intensifies after the leaves drop in autumn.
These shrub forms generally lack the large, showy bracts of the tree dogwoods, instead producing clusters of tiny, four-petaled white flowers in flat-topped arrangements called cymes. They often spread aggressively by underground stems, or rhizomes, forming dense thickets that make them effective for erosion control along stream banks. Their fruit is typically a small, white or blue drupe, which is often consumed by birds.
At the smallest end of the spectrum is the Bunchberry (Cornus canadensis), one of the few herbaceous dogwoods that grows as a creeping, perennial groundcover. This tiny plant rises only four to eight inches, spreading via woody stolons to form a carpet-like mat. The Bunchberry still possesses the characteristic dogwood flower structure, with four white bracts surrounding a central cluster of inconspicuous flowers, mirroring the appearance of a full-sized dogwood tree on a miniature scale.
Key Distinctions for Identification
Identifying a dogwood involves focusing on a few physical traits consistent across most species. The most reliable feature is the pattern of the leaf veins, known as arcuate venation, where the lateral veins curve noticeably upward as they approach the leaf margin. This creates a signature “fingerprint” unique to the genus.
A simple field test, known as the “dogwood string test,” involves gently tearing a leaf across the middle and slowly pulling the two halves apart. The interconnected vascular bundles, which are elastic and thread-like, will stretch and remain visible between the two torn pieces. This feature helps differentiate a dogwood from other trees with similar leaf shapes.
The bark texture of mature trees also provides a reliable distinction between the major varieties. The Eastern Flowering Dogwood (C. florida) develops a distinctive, blocky bark that resembles alligator skin, while the Kousa Dogwood (C. kousa) is characterized by a mottled, exfoliating bark that peels away in irregular patches. Observing the difference between the true flowers, which are tiny and clustered, and the showy, petal-like bracts is another way to confirm a dogwood’s identity.