Cornus unalaschkensis Ledeb. — Western bunchberry dogwood

Introduction

Western bunchberry dogwood is the North Pacific member of Arctocrania, forming low clonal colonies in maritime coniferous forests, wet heaths, boggy woodland, and moist forest floors from the Russian Far East through Alaska and western Canada to the northwestern United States and locally California. Its rhizomes persist beneath or within the moss layer, and in exceptionally humid Pacific temperate rainforest the plant can even establish on moss-covered logs or trunks (Deasy et al. 2026).

For decades Cornus unalaschkensis was explained as an allotetraploid species produced by hybridization between C. canadensis and C. suecica. The modern genomic picture is more intricate. Sun et al. (2025) recovered multiple unalaschkensis-associated ancestries and concluded that the species evolved within the broader canadensis-derived radiation during the Pleistocene, with ploidy shifts, introgression, and repeated hybridization layered onto that history. Tree TSAR therefore treats C. unalaschkensis as an accepted species with a reticulate evolutionary history, not as a simple contemporary hybrid formula.

Tree TSAR recognizes two cryptic subspecies: ssp. unalaschkensis and ssp. borealis [Y.X.Sun, W.B.Zhou & Q.-Y.Xiang] TSAR*, corresponding broadly to the Cu1/admixture complex and Cu2 genomic ancestry identified in 2025. The historical names C. canadensis var. intermedia and C. intermedia are retained with the nominate lineage rather than confused with C. × lepagei.

Horticultural and Agricultural Uses

Cultivation resembles that of C. canadensis: cool, acidic, consistently moist soil with conditions approximating open woodland is ideal. Plants are well adapted to cold but resent sustained heat and drying. Because the species spreads rhizomatously, a successful plant can gradually form a colony rather than remaining a single crown (Deasy et al. 2026).

The two Tree TSAR subspecies have no established horticultural distinction. For gardens this may be inconsequential, but for germplasm collections and research it makes provenance important. Material from the Pacific Northwest sits within the most genetically complex part of the bunchberry radiation and should retain locality data whenever possible.

Conservation Concerns

Western bunchberry dogwood is globally common enough that NatureServe ranks it G5, and the broad species is not currently considered globally threatened. Local status can be very different; California, for example, treats it as a rare plant of conservation concern even though the species is secure across its full range (NatureServe 2026; Calflora 2026).

The 2025 genomic study adds a second dimension to conservation: C. unalaschkensis contains cryptic geographic structure that is invisible in a species-only occurrence map. Protecting a broad range of populations, especially across the Cu1–Cu2 and introgression zones, better preserves the evolutionary history of the species than treating every colony as interchangeable (Sun et al. 2025).

Additional Information

Trees and Shrubs Online (opens in a new tab) — Detailed modern treatment incorporating the 2025 genomic results.
Plants of the World Online (opens in a new tab) — Accepted global backbone, synonymy, and distribution.
Flora of North America (opens in a new tab) — North American morphology, habitat, and range.
NatureServe Explorer (opens in a new tab) — Global conservation-rank context.
Calflora (opens in a new tab) — California occurrence and regional conservation context.

References and Further Reading

Calflora (2026) Cornus unalaschkensis. Calflora. https://www.calflora.org/app/taxon?crn=14533 (opens in a new tab)

Deasy M, Crowley D, Aldridge J, Chişu R (2026) Cornus unalaschkensis. Trees and Shrubs Online. https://www.treesandshrubsonline.org/articles/cornus/cornus-unalaschkensis/ (opens in a new tab)

Flora of North America Editorial Committee (2016) Cornus unalaschkensis. Flora of North America North of Mexico, Vol. 12. https://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=242443975 (opens in a new tab)

NatureServe (2026) Cornus unalaschkensis. NatureServe Explorer. https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.139123/Cornus_unalaschkensis (opens in a new tab)

Royal Botanic Gardens, Kew (2026) Cornus unalaschkensis Ledeb. Plants of the World Online. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:271698-1 (opens in a new tab)

Sun Y, Zhou W, Xiang Q-Y (2025) Genomic data uncover complex hybridization and evolutionary history of the bunchberry species complex (Cornus L., Cornaceae). Horticulture Research 12(5): uhaf026. https://doi.org/10.1093/hr/uhaf026 (opens in a new tab)