Morphotypes of plant macrofossil assemblages of the basal unit of the Upper Cretaceous (Turonian?–Santonian) Comox Formation, Nanaimo Group, Vancouver Island, were investigated to provide insight into the character of the macroflora, environment of deposition, and paleogeography of Vancouver Island. Three floristic assemblages were documented: one dominated by angiosperm morphotypes such as Platanus, Menispermites, and Zizyphus-like leaves; another dominated by gymnosperm morphotypes such as those synonymous with Glyptostrobus comoxensis Bell and Pseudoctenis latipennis (Heer) Seward; and a third assemblage transitional between the previous two. These assemblages suggest the Saanich Member was likely deposited in a barrier island – estuarine floodplain complex with fluvial sedimentary input. The macrofloral assemblage also includes many endemic taxa, suggesting a barrier to floral migration between the paleocontinent and the Vancouver Island precursor during the Upper Cretaceous, which supports the existence of a third floristic province in North America during the Upper Cretaceous.

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