Which species of yew is the source of the anticancer drug paclitaxel?

Taxus brevifolia, the Pacific yew, is the yew species that supplied the original natural source of the anticancer drug paclitaxel.

Pacific yew is native to the forests of western North America, from southeastern Alaska and British Columbia through the Pacific Northwest into northern California. In the 1960s, researchers examining plants collected in a U.S. National Cancer Institute screening program found promising anticancer activity in extracts of its bark. The active compound was later identified as paclitaxel, originally known by the brand name Taxol.

Paclitaxel disrupts cell division by stabilizing microtubules, structures that chromosomes need to separate during mitosis. That mechanism makes it useful against several cancers, including ovarian, breast, and lung cancers, although treatment depends on the disease and clinical setting.

A common mix-up is saying Pacific yew is still the only commercial source. Heavy bark harvesting threatened wild trees, and modern production relies substantially on semi-synthesis from related cultivated yews, especially Taxus baccata. The red aril around a yew seed is not the same as the highly poisonous seed, leaves, and bark.