Differential Morphology: Yew & Eastern Hemlock

“Learn the poisons first” is a common motto of mine. If we learn the toxic species of our area, it makes getting comfortable with the plants that are safe as edibles as medicinals a lot easier. A great way for folks to do this is to pick a particular botanical subtype, like a genus, family, or general category of plants, and learn all the local toxic species in that group. For example, we can take the category of needle-bearing evergreen trees of the central and northeastern seaboard. With non-needle-bearing evergreens like Holly and Rhododendron excluded, there is only one toxic genus to get familiar with: The Taxus genus, or Yew. 

Taxus spp.

Ethnobotany of Yew

In the eastern United States, yew is encountered primarily as ornamental plantings of European, Japanese, or hybrid species, though the native shrubby Canada Yew (Taxus canadensis) occurs in scattered populations throughout the northern Appalachians and Great Lakes region. Due to their shade-tolerance, adaptability to polluted soils, and tolerance of hard pruning, it is very common to see Yew planted in cities of Pennsylvania, and these are usually Japanese Yew (Taxus cuspidata) or the hybrids, like the Anglo-Japanese Yew (Taxus × media). Especially with the prevalence of hybridization among the genus, distinguishing Yew Taxus species from each other can be incredibly difficult, sometimes needing microscopic analysis. Some botanists believe they should all be considered subspecies under a single global species.

Yew is commonly planted in urban environments and pruned into a dense hedgerow

Yew arils

The chemistry of yew is dominated by a group of diterpenoid alkaloids known as taxines. These compounds are concentrated throughout the needles, bark, seeds, and wood and act primarily on cardiac tissue, disrupting normal electrical conduction in the heart. Unlike many plant poisons that cause progressive gastrointestinal distress before more serious symptoms develop, taxine poisoning can result in a rapid onset of cardiovascular collapse. The fleshy red aril surrounding the seed lacks taxines and is technically edible, though the seed within remains highly toxic and should never be consumed. As a young botanist I always found this amusing because it goes against the broadbrush (and erroneous) rule that “red berries are toxic,” as the red part of Yew tree is the only part which is not. 

In spite of its toxicity, Yew has held a place in the traditional materia medica of Indigenous peoples all across the world. In North America, from the Mi'kmaq of the Atlantic northeast to the Salish of the Pacific northwest, Yew has been valued for tool-making, medicine, and ceremonial practices. Among North American yews, the Pacific yew (Taxus brevifolia) generally contains comparatively lower concentrations of taxine alkaloids, especially during the growing season. This may help explain why Indigenous peoples of the Pacific Northwest developed a broader range of uses for the species than has been recorded for yews in other regions. It had a place in European, Asian, and SWANA traditions as well. In fact, the oldest known wooden weapon ever found was made from Yew; The Clacton Spear was found in the Clacton-on-Sea in England in 1911 and is estimated to be 400,000 years old. 

Like so many other low-dose, high toxicity herbs, use of this genus has fallen largely out of favor due to safety concerns and a general loss of applied knowledge about how to safely work with it. There is no effective antidote and very little in the way of treatment options for poisoning and the therapeutic index (safe margin of use) is extremely small. So even though there are relatively few cases of Yew poisoning in humans, and the overwhelming majority of those severe and fatal yew poisonings stem from deliberate ingestion, it is still a highly risky practice to work with Yew internally. In 1962,  the Pacific yew (Taxus brevifolia) was collected as part of an extensive U.S. government initiative to screen tens of thousands of plant extracts for anti-cancer compounds. Researchers isolated paclitaxel from the bark, which prevent cancer cells from spreading. Paclitaxel  went on to be marketed as the pharmaceutical drug Taxol. Today, paclitaxel and related taxanes are produced through cultivation and semi-synthetic methods, reducing pressure on wild Yew populations. Nevertheless, in terms of modern ethnobotanical relationships, the Taxus genus is high up on the list of heavily valued upon plants.

Differential Morphology

Yews are flat needled trees and shrubs. They have short, soft, blunt tipped needles with alternate leaf arrangement. Their needles are directly attached to the stem. Yew’s flat needles make them look-alikes for two genera of edible and medicinal trees here in the east coast: the Eastern hemlock (Tsuga canadensis) and the Firs (Abies genus). 

There are a number of differentials to look for, but they can be easily mistaken.

The bark of Eastern Hemlock is gray and slightly scaly and plated while young but developing in flat, deep furrows, whereas Yew bark tends to remain more flaky or peeling, and is purplish-brown in color.

Yew bark

Hemlock bark

The upright cones of Abies are easy to differentiate from Hemlock and Yew, but the male Yews produce small pollen cones that look similar to the Eastern Hemlock’s pollen cones. Yews being dioecious, the red female arils may not always be present, but Hemlocks are monoecious so you could look for their seed cones. 

The arrangement of the needles is also an identifier. Firs are the easier to identify due to their sessile attachment (they lack a petiole, or leaf stem) and their conspicuous leaf scars, which look like tiny suction cups at the remnant base of each needle. Fir needles also spiral around the stem, whereas Yew and Hemlock are spread evenly in two distinct rows, creating a fanned out, single plane arrangement. Yews are denser, and more regular and “comb-like” in distribution, while Hemlock are more sparse, irregular, and “feather-like,” though without seeing the two side by side this isn’t a very solid differential to go by.

So what is that differential, you ask? The underside of the needle.

Yew underside (no stomatal striping)

Hemlock underside (with stomatal striping)

Flip over an Eastern Hemlock or Fir needle and you'll find two distinct white stomatal bands. Once you've seen them a few times, they become hard to miss. Yew lacks these bright white bands. The underside is green, sometimes slightly lighter than the upper surface, but never starkly striped.

Eastern Hemlock Ethnobotany

In my experience, a lot more folks are familiar with Hemlock than Yew, and ironically they tend to be more concerned with the possibility of Hemlocks being toxic due to the common mix-up with their moniker sharing Poison Hemlock (Conium maculatum). Conium, however, is an herbaceous plant in the Carrot family (Apicaea). Their similarities really end there, at the common name, so you can safely enjoy the Eastern Hemlock in all it has to offer as a medicinal and edible tree. 

Tsuga canadensis

Tsuga canadensis is a prolific keystone species of riparian forests of the full length of Appalachian mountain range, and extending through the Northeastern U.S, as far west as the Great Lakes region, and into southeastern Canada.

They make a wonderful addition to a bioregional apothecary as an astringent, vulnerary, antimicrobial, nutritive expectorant. All parts of this conifer are medicinal.

The inner bark and sap are high in tannins and highly antimicrobial, making them a great option as a decocted wash for skin irritation, wounds, and burns, and as a gargle sore throat. 

The needles are rich in vitamins and volatile compounds including α-pinene, limonene, and caryophyllene which have an bronchodilating and expectorant effect that can be harnessed as a fresh tea or steam.

While I can be seen munching on hemlock needles all year long, the best time to eat them is in the spring when the bright lime-green new growth emerges at the tips of each branch. These verdant young tips are tender and citrusy, and tend to be much higher in vitamins like vitamin C, minerals like magnesium, and carbohydrates, making them a relatively nutrient dense trail-side snack. The mature, dark-green needles are high in calcium and fiber and are fine to eat in moderation.

Just be sure to practice your five steps of positive identification, and flip over enough needles to get comfortable with ID before you taste them. In addition to the species identification, it's important to note that some Hemlock trees are treated with pesticides like imidacloprid or dinotefuran for the Woolly Adelgid (Adelges tsugae), which can accumulate in the tree's tissue and remain there for months after treatment. Management practices vary widely, but it is most common in National Parks and public-facing areas in smaller state parks and state forests, and especially in any areas designated as old-growth or high value, such as in Cook Forest State Park and Ricketts Glen State Park. If you’re unsure about the status of the tree, ask the property managers before foraging. 

Both the Eastern Hemlock and the Yew have extensive and beautiful ethnobotanical histories and modern relevance among the people who inhabit their ecosystems. Investing time to get to know toxic species is as important as spending time with the accessible edible and medicinal plants, not only from a safety and plant identification standpoint, but as a way of deepening our understanding of the tapestry of plants that create the infrastructure of our human culture.