Coastal bunchberry, western bunchberry, or Alaskan bunchberry, is native to western North America and extreme eastern Russia. According to the Flora of North America account of Cornus unalaschkensis, the species inhabits “maritime copse or heath, maritime coniferous forests and bog woodlands, moist broadleaf or coniferous forests” from elevations of 0 to 3000m (to 10000 ft.).
This entry is a companion to one from a decade ago for the similar-in-appearance Cornus canadensis. However, one of the key morphological differences between the species is visible in both entries; Cornus unalaschkensis has petals that are at least partially purple, while Cornus canadensis has white to greenish-white petals. Do note that the inflorescence for each of these species is a pseudanthium (“false flower”), in which a cluster of small flowers (or florets) forms what appears to be a single flower. In this instance, the 3 clusters of purple-tinged florets are each subtended by 4 white involucral bracts that have the appearance of flower petals.
Once you know this as a difference between the two species, they become relatively easy to distinguish when in flower. Geography is a clue as well; Cornus canadensis tends to occur from the Rockies eastward, while Cornus unalaschkensis tends to be more associated with the coast even within its broader western North American / eastern Russian range. In local horticulture (and even in some field guides), Cornus unalaschkensis will sometimes be ignored in favour of Cornus canadensis; it always makes me frown when I encounter Cornus canadensis on local “recommended native plant lists” instead of the true local native, Cornus unalaschkensis. An overreaction, perhaps–as a transplant to Canada’s west coast from the native range of Cornus canadensis, I’m sure I wrongly assumed its identity as well, until corrected by a reference like Plants of the Pacific Northwest Coast.