Taxus

Yews, the common name for the genus *Taxus*, are coniferous trees or shrubs in the family Taxaceae. They grow across the northern hemisphere's temperate zones, from as far north as Norway down to the South Celebes, with some populations also found in tropical highlands. The oldest known fossils of these plants date to the Early Cretaceous.

These plants grow slowly and can live for a very long time, reaching heights between 2.5 and 20 meters. Their bark is reddish, and their leaves are flat, lance-shaped, dark green, and arranged spirally on the stem, though the leaf bases twist to form two flat rows. Male cones are small and globe-shaped, releasing pollen in early spring. Most yews are dioecious, but some individuals can change sex or be monoecious. The seed cones are highly modified: each holds a single seed partly wrapped in a soft, bright red, berry-like structure called an aril, which is open at the end. Birds like thrushes and waxwings eat the arils and disperse the hard seeds in their droppings, with the arils maturing over two to three months to improve seed dispersal.

The Latin word *Taxus* likely came from the Scythian word *taxša*, meaning both "yew" and "bow," as the Scythians used yew wood for bows. All yew species are closely related, and some botanists consider them all subspecies or varieties of a single widespread species, *Taxus baccata*, the first scientifically described yew. Classification varies widely: in 1903, RKF Pilger grouped all yews under *T. baccata*, while in 2007, R. W. Spjut split them into 25 species and over 50 varieties based on small differences. Geographic distribution has traditionally guided species identification, but Asian species are harder to classify. *Taxus contorta* in the Western Himalaya and *Taxus sumatrana* in Malesia are generally accepted, but overlapping ranges in the Eastern Himalaya, China, and subtropical Southeast Asia have caused confusion. Species like *Taxus chinensis*, *Taxus mairei*, and *Taxus wallichiana* were only clarified in the 21st century using molecular phylogenetics. The most distinct is the Sumatran yew (*T. sumatrana*), with sparse, sickle-shaped yellow-green leaves. The Mexican yew (*Taxus globosa*) is also relatively distinct, with foliage between that of the Sumatran yew and other species. The Florida yew, Mexican yew, and Pacific yew are rare and listed as threatened or endangered.

Yews typically grow in the understory or canopy of moist temperate or tropical mountain forests. Their elevation ranges from 3,000 meters in tropical forests to near sea level at their northernmost limits. They are common in landscaping, leading to widespread naturalized populations in the United States, where *T. baccata* and *Taxus cuspidata* are popular ornamental shrubs. *T. baccata* is found across Europe and into western Asia, while *T. cuspidata* occurs in East Asia, including China, Japan, Korea, and Sakhalin. *Taxus brevifolia* ranges from California to Montana and Alaska in the United States, and *Taxus canadensis* appears in the northeastern United States and southeast Canada.

Plants of the World Online recognizes 12 confirmed species. Extinct fossil species include *Taxus engelhardtii* from the Oligocene of Bohemia, *Taxus inopinata* from the Upper Miocene, *Taxus masonii* from the Eocene Clarno Formation in Oregon, and *Taxus schornii* from the Miocene of northern Idaho. Common hybrids include *Taxus × media* (*T. baccata* × *T. cuspidata*) and *Taxus × hunnewelliana* (*T. cuspidata* × *T. canadensis*).

All yew species contain highly poisonous taxine alkaloids, with some variation between species. Every part of the tree except the arils contains these alkaloids. The arils are edible and sweet, but the seed inside is dangerously poisonous: unlike birds, the human stomach can break down the seed coat, releasing toxins that can be fatal if the "berries" are eaten without removing the seeds. Grazing animals like cattle and horses sometimes die after eating yew leaves, though deer can break down the poisons and browse yew freely, often restricting wild yews to cliffs and steep slopes. The foliage is also eaten by the larvae of some Lepidoptera, such as the moth willow beauty.

All parts of a yew plant are toxic to humans except the arils (which still contain a toxic seed). Male and dioecious yews release cytotoxic pollen, which can cause headaches, lethargy, aching joints, itching, skin rashes, and trigger asthma. These pollen grains are extremely small and can pass through window screens.