American Yew

What is American yew?

The American yew (Taxus canadensis) is a prostrate, straggling evergreen shrub belonging to the Taxaceae family. Native to northeastern North America, it is recognized as the hardiest species of yew, typically reaching heights of about 1 metre (3 feet). It features small, yellowish-green leaves that taper to a point and serves as an excellent ground cover in forested regions.¹

It is important to note that “American yew” is also used as a lumber trade name for the Pacific yew. While the American yew is a distinct shrubby species, the broader Taxus genus is known for its slow-growing, long-lived evergreens. Like other yews, the foliage and seeds of these plants contain a poisonous alkaloid that can be fatal to livestock.¹²

How does the Pacific yew differ from the American yew?

The Pacific yew (Taxus brevifolia) and the American yew (Taxus canadensis) are distinct species within the Taxaceae family, primarily differing in their growth habits and commercial utility.

• Growth Habit: The American yew is a prostrate, straggling shrub that typically reaches only about 1 metre (3 feet) in height, making it an effective ground cover in northeastern North America. In contrast, the Pacific yew is an evergreen timber tree that usually grows between 5 and 15 metres (15 to 50 feet) tall, occasionally reaching 25 metres.⁴⁵
• Commercial Importance: The Pacific yew is the only commercially significant yew native to North America. Its bark is a known source of taxol, a potent cancer treatment. While the American yew is a distinct species, the name “American yew” is also sometimes used as a lumber trade name for the Pacific yew.⁵¹⁴

Both species share the characteristic toxicity of the yew genus, as their foliage and seeds contain alkaloids that can be fatal to livestock.²

Why is the alkaloid taxol found in yew trees important for medicine?

Taxol is a vital anticancer compound originally isolated from the bark of the Pacific yew (Taxus brevifolia). Its medical importance lies in its unique ability to disrupt cell division by interfering with the separation of nuclear chromosomes, making it highly effective against cancers of the breast, ovary, lung, head, and neck.⁶⁵

The discovery of taxol emerged from screening programs investigating the biological effects of the yew family, which have a long history of use in traditional medicine for conditions like arthritis and fever. While early production required harvesting the bark of old-growth trees—sparking significant environmental concerns regarding the spotted owl habitat—the development of a semisynthetic process using renewable needles and twigs eventually allowed for sustainable production without destroying yew forests.⁵⁶

What makes the stinking yew different from other yew species?

The stinking yew (Torreya taxifolia) is often confused with true yews, but it is distinct in several key ways:

• Classification: While it belongs to the same family (Taxaceae), the stinking yew is part of the genus Torreya, whereas true yews belong to the genus Taxus.
• Odor: The most notable difference is that the stinking yew’s leaves, wood, and seeds emit a disagreeable, fetid odor when bruised or crushed, a trait not found in true yews.³²
• Physical Characteristics: The leaves of the stinking yew are spiny-pointed and relatively hard and rigid compared to the softer, flattened leaves of Taxus species. Additionally, its seeds are surrounded by plumlike arils, whereas true yews feature a fleshy, cup-shaped red aril.³⁷⁸
• Conservation Status: Unlike many widespread Taxus species, the stinking yew is a critically imperiled endangered species with a very limited natural distribution in western Florida and southwestern Georgia.³