Flora of North America species comparison

As the synonymy implies, Cornus sericea has received considerable attention from taxonomists wishing to subdivide the species, presumably in order to make it more comprehensible. Most of the divisions have been based upon indumentum and stone differences, although habit has also been used. Although one of the synonyms and one of the common names imply a stoloniferous habit, the species is not stoloniferous; evidently, branch tips infrequently arching to the ground and rooting at the nodes led to confusion regarding the growth habit. H. W. Rickett (1944b) examined the morphology of the various forms, varieties, and subspecies, and found extensive overlap using fruit shape and indumentum differences. It is not known whether the variation is due to primary differentiation or secondary intergradation, and the complex is treated here as a single species. There is little doubt that the European species C. alba Linnaeus is closely related to C. sericea and should be included in any future studies of this species complex.

The name Cornus stolonifera has sometimes been applied to C. sericea (for example, H. W. Rickett 1944b) because the description by Linnaeus of the latter could apply to several currently recognized species. F. R. Fosberg (1942) lectotypified C. sericea, establishing that it applies to this species.

Cornus sericea is commonly planted as an ornamental and occasionally escapes; plants in suburban areas and in highly acidic soils are suspected as non-natural occurrences. Putative hybrids between C. sericea and C. rugosa have been called C. ×slavinii Rehder, and are reported from Maine, New York, Ontario, Prince Edward Island, and Wisconsin.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

H. W. Rickett (1934) argued that the description of Cornus obliqua by Rafinesque is inadequate to associate that name with a species; that assessment is not accepted here. The description by Rafinesque of the plants having reddish brown, slightly rugose bark, narrowly elliptic to lanceolate discs, and whitish yellow abaxial leaf surfaces, along with the cited locality of the Kentucky River, clearly delineates this species. Rafinesque was the first to divide the blue-fruited dogwood of L. Plukenet (1691–1705, part 4) into two species.

Cornus obliqua and C. amomum can be distinguished not only by the differences included in the key above, but also by their abaxial leaf cuticle, which is coronulate in C. obliqua but not in C. amomum, but seeing this character requires high magnification. However, in much of the area where they are sympatric (Connecticut, District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New York, Tennessee, and Vermont), many individuals show intermediate leaf blade abaxial surface and hair morphology. They are detected by having both the whitish leaf blade abaxial surface and appressed hairs of C. obliqua with occasional scattered erect, often tan to brown hairs, similar to those typical for C. amomum. J. S. Wilson (1964) concluded that differences in leaf surface and hair morphology are environmentally based (sun versus shade), whereas work by Z. E. Murrell (1992) documented a geographical basis for the differences. The geographical zone of intermediacy needs greater scrutiny to determine its full extent and whether the intermediacy of many plants represent hybridization or incomplete speciation.

A putative hybrid between Cornus obliqua and C. racemosa, reported from Massachusetts, Ohio, and Pennsylvania, has been called C. ×arnoldiana Rehder [= Swida arnoldiana (Rehder) Soják].

(Discussion copyrighted by Flora of North America; reprinted with permission.)