Plants of National Botanical Significance: Thank Yew! A Cancer-fighter from the Forest Floor

In mature forests, the towering trees attract most of the attention, but, sometimes, the less dominant plants also have interesting stories to tell. Dwelling in the shady understory of eastern North American forests is a prostrate, spreading shrub with national botanical significance in Canada because of its crucial role in human medicine. The Canada yew, Taxus canadensis, thrives in the rich soils beneath canopies of balsam fir, spruce, and mature hardwoods. They can be seen around Ottawa forming a healthy groundcover in Pinhey Forest and along the Jock River.

The Canada yew grows in a sprawling mass, reaching a height of no than 5 feet but spreading up to 8 feet wide. Colonies form when branches touch the ground, take root and sprout, gradually making an expansive mat. The inch-long flat evergreen needles are dark glossy green with a paler, striped underside. The pointy-tipped needles are arranged in a spiral around the twig. Still, the branches have a flattened appearance because the upper and lower needles twist sideways. As with other conifers, the separate female and male flowers are easily overlooked. Found in the leaf axils, these small cone-like structures – strobili – resemble scaly buds. 

The most eye-catching feature of the yew is its cone. Unlike most conifers’ dry, woody cones, yew cones are bright red arils – fleshy cups opened at one end to reveal a large seed. Birds such as cedar waxwings, thrushes, and ruffed grouse feed on the arils and are the primary agents of seed dispersal.

Because of its dependence on mature forests, Canada yew is highly intolerant of logging, fire, and other major disturbances. Climate change may also threaten this species as it grows best in a stable environment with steady moisture levels. In the past, harvesting was a significant threat to yew populations. 

In the 1970s, anti-cancer alkaloids were discovered in the bark of the western yew, Taxus brevifolia. The cancer drug Paclitaxel was developed from it. Harvesting sparking declines in wild populations. Looming shortages spurred research into other yew species. Canada yew was found to have the same desired compounds. Thank yew!

Today, Canada’s yew nursery industry provides ingredients for cancer drugs without further depleting wild populations.

Canada yew will be a part of Canadensis, the national botanical garden of Canada in Ottawa.