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Introduction
Arnold dogwood (Cornus × arnoldiana) is the named natural hybrid between blue colonel dogwood (C. obliqua) and gray dogwood (C. racemosa). Both parents belong to Subgenus Thelycrania, and the hybrid is most likely to occur where their eastern North American ranges overlap. The original Arnold Arboretum account appeared in 1924, making this one of the long-recognized named hybrids among the shrubby dogwoods (Arnold Arboretum 1924).
The parental formula requires historical context. Older floristic and horticultural literature often treated C. obliqua inside C. amomum, so the hybrid may appear as C. amomum × C. racemosa. Tree TSAR follows the modern accepted species circumscriptions and therefore uses C. obliqua × C. racemosa. Recent field work has again shown how readily plants with the expected mixed characters can be overlooked among superficially similar members of Subgenus Thelycrania (Connolly 2022).
Horticultural and Agricultural Uses
Arnold dogwood has no established commercial horticultural role comparable with red-stem dogwoods or named gray-dogwood cultivars. Its chief horticultural importance is diagnostic: hybrid individuals can combine characters of two species that are already difficult to identify when sterile, and cultivated or spontaneous plants should not be forced into a parent species solely from one leaf or stem character.
Where the hybrid is maintained in living collections, both provenance and the identities of nearby parent populations are unusually valuable. Voucher specimens and, where possible, DNA-quality material can help distinguish true hybrids from unusual individuals of either parent.
Conservation Concerns
No independent global conservation assessment is appropriate for Cornus × arnoldiana. Its persistence depends on the continued coexistence of C. obliqua and C. racemosa and on ecological settings in which pollen exchange can occur.
From a conservation perspective, the hybrid is best treated as evidence of ongoing gene flow within Subgenus Thelycrania. Protecting parent populations and their contact zones preserves both the parental lineages and the evolutionary process that produces the hybrid.
Additional Information
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Trees and Shrubs Online (opens in a new tab) - Current hybrid account and modern parentage context.
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Plants of the World Online (opens in a new tab) - Current Kew search for the named hybrid.
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Biodiversity Heritage Library (opens in a new tab) - Original 1924 Arnold Arboretum publication.
References and Further Reading
Arnold Arboretum (1924) Cornus arnoldiana. Bulletin of Popular Information, Arnold Arboretum 10(12): 45. Link (opens in a new tab)
Connolly B (2022) Hybrids hiding in plain sight. Arnoldia 79(2). Link (opens in a new tab)
Murrell ZE, Poindexter DB (2016) Cornaceae. In: Flora of North America Editorial Committee (eds) Flora of North America North of Mexico, vol. 12. Oxford University Press, New York and Oxford. Link (opens in a new tab)
Du Z-Y, Xiang Q-Y, Cheng J, Zhou W, Wang Q-F, Soltis DE, Soltis PS (2023) An updated phylogeny, biogeography, and PhyloCode-based classification of Cornaceae based on three sets of genomic data. American Journal of Botany 110(2): e16116. Link (opens in a new tab)