| Taxus brevifolia | |
|---|---|
 | |
| Taxus brevifolia (Pacific yew) foliage and fruit | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnospermae |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Cupressales |
| Family: | Taxaceae |
| Genus: | Taxus |
| Species: | T. brevifolia |
| Binomial name | |
| Taxus brevifolia | |
 | |
| Natural range | |
| Synonyms[2][3] | |
| |
Taxus brevifolia, thePacific yew orwestern yew, is aspecies of tree in the yewfamilyTaxaceae native to thePacific Northwest ofNorth America. It is a smallevergreenconifer, thriving in moisture and otherwise tending to take the form of ashrub.
A smallevergreenconifer (sometimes appearing as ashrub),[4] the Pacific yew grows to 10–15 metres (33–49 feet) tall and with a trunk up to 50 centimetres (20 inches) in diameter, rarely more. In some instances, trees with heights in excess of 20 m (66 ft) occur in parks and other protected areas, quite often in gullies. The tree is extremely slow growing, and has a habit of rotting from the inside, creating hollow forms. This makes it difficult and sometimes impossible to make accuratering counts to determine a specimen's true age. Often damaged bysuccession of the forest, it usually ends up in a squat, multiple-leader form, able to grow new sprouts from decapitated stumps.[4] In its shrub form, sometimes called "yew brush", it can reproduce vegetatively vialayering.[4]
It has thin, scalybark, red then purplish-brown,[4] covering a thin layer of off-white sap wood with a darkerheartwood that varies in color from brown to a purplish hue to deep red, or even bright orange when freshly cut.[4] Theleaves are lanceolate, flat, dark green, 1–3 cm (3⁄8–1+3⁄16 in) long[4] and2–3 millimetres (3⁄32–1⁄8 in) broad, arranged spirally on the stem, but with the leaf bases twisted to align the leaves in two flat rows either side of the stem except on erect leading shoots where the spiral arrangement is more obvious.
Theseed cones are highly modified, each cone containing a singleseed4–7 mm (3⁄16–1⁄4 in) long partly surrounded by a modified scale which develops into a soft, bright redberry-like structure called anaril,[4]8–15 mm (5⁄16–9⁄16 in) long and wide and open at the end. The arils are mature 6–9 months after pollination. The seeds contained in the arils are eaten bythrushes and otherbirds, which disperse the hard seeds undamaged in their droppings; maturation of the arils is spread over 2–3 months, increasing the chances of successful seed dispersal. The male cones are globose,3–6 mm (1⁄8–1⁄4 in) diameter, and shed theirpollen in early spring. It is mostlydioecious, but occasional individuals can be variablymonoecious, or change sex with time.[citation needed]
T. brevifolia var.reptaneta (thicket yew) is a shrub variety that generally occurs in the mid to upper elevation range of the typical variety, 1,000–1,220 m (3,280–4,000 ft) at its southernmost occurrence in theKlamath Mountains region, and at lower elevations further north.[5] It is distinguished from young trees of the typical variety (var.brevifolia) by its stems initially creeping along the ground for a short distance before ascending (curving) upwards and by the branches growing off to one side of the stem, usually the upper side.[6] The epithetreptaneta is from the Latinreptans which means "creeping, prostrate, and rooting",[7] which is exactly what this variety does; in rooting it forms yew thickets; hence, the epithetreptaneta (-etum means "collective place of growth") and hence the common name, thicket yew.
Unlike the typical variety, thicket yew grows in abundance on open sunny avalanche shoots or ravines as well as in the forest understory. It also occurs along forest margins. In northwestern Montana, a variant of the thicket yew does not ascend upwards; rather, it remains along the ground.[5] This is probably the ancestral form; the upright form with branches along the upper side would be the expected growth pattern that might evolve from one with stems that strictly creep along the ground since branches can only arise from the upper surface.
T. brevifolia var.reptaneta has been described as synonymous with typical yew (var.brevifolia). Though the two varieties may be genetically distinct, some botanists only use this taxon to describe different geographical ranges. For example,T. mairei var.speciosa, which occurs with the typical variety in southern China in 10 of 13 provinces, was rejected for the lack of a "geographic reason" for recognition[8] though it appears genetically distinct.[9]T. brevifolia var.reptaneta has also been proposed to be elevated to asubspecies, despite that rank being used to define geographically separated groups ofT. baccata.[10][a]
TypicalT. brevifolia, like most species in the genus, usually produces a single ovule on a complex scaly shoot, composed of a primary shoot and a secondary short shoot. To the casual observer they appear as one funnelform shoot with an ovule at the apex.[12]T. brevifolia var.polychaeta differs from var.brevifolia in producing a relatively longer primary shoot[5] with as many five secondary shoots.[13] The epithet,polychaeta, is in reference to the primary shoot resembling apolychaete worm; hence, its common name 'worm cone yew'. Varietypolychaeta appears to be relatively rare. It may have beenextirpated from the type locality—aroundMud Bay nearOlympia, Washington—as a result of urban expansion. It is also known from Northern Idaho andSonoma County, California.[5][14]
As in the case with thicket yew, worm yew has been indicated to be the same as the typical variety, but again there are no specific studies to support this conclusion. The authority of thicket yew and worm cone yew has been involved in the study ofTaxus for 25 years at the time the varieties were described.[5][15]
Yew foliage is very similar to that ofSequoia sempervirens, the coastal redwood.[4]
Pacific yew isnative to thePacific Northwest. It ranges from southernmostAlaska south toNorthern California, mostly in thePacific Coast Ranges, but with isolateddisjunct populations in southeastBritish Columbia and inNorthern Idaho.[16][17][18][19][20][21] It grows in varying types of environments; however, in drier environments it is mostly limited to stream-side habitats, whereas in moist environments it will grow up onto slopes and ridgetops,[16] at least as high in altitude as 1,400 metres (4,600 ft) above sea level.[4] Pacific yew isshade tolerant, but can also grow in sun.[22] The tree's shade tolerance allows it to form anunderstory, which means that it can grow along streams providing shade to maintain water temperature.[23]
Birds eat the fruit cups and spread the seeds.[24] Moose feed on the tree in winter in forests of theRocky Mountains.[4]
Many parts of yews are poisonous and can be fatal if eaten, including the seed which should not even be chewed.[24]
Traditionally, the resilient and rot-resistant wood was used byNative Americans to make tools, bows (backed with sinew), arrows, and canoe paddles.[4] Other purposes for yew included making harpoons, fishhooks, wedges,clubs, spoons, drums, snowshoes, and arrowheads.[4] The foliage and bark was used for medicinal purposes.[4] Members of thePit River Tribe would sell this plant to theUkiah.[25] TheConcow tribe calls the treeyōl’-kō (Konkow language).[26]
Modern-daylongbow makers report that a very small percentage of yew trees are of a grain suitable for their craft.[4] TheJapanese have used the wood for decorative purposes,[16] and the Taiwanese have valued it as well.[4]
The juicy red cup around the seed seems to be edible (but not the toxic seed within),[24] with a mild cherryjello-like flavour.[4] The berry is said to have a sweet taste but slimy texture, while the leaves, bark and seed are extremely poisonous and should not be consumed.[27]
Thechemotherapy drugpaclitaxel (taxol), used inbreast,ovarian, andlung cancer treatment, can be derived fromT. brevifolia[28] and other species of yew. As it was already becoming scarce when its chemotherapeutic potential was realized around the 1990s, the Pacific yew was never commercially harvested from its habitat at a large scale; the widespread use of the paclitaxel was enabled circa 2003 when a semi-synthetic pathway was developed from extracts of cultivated yews of other species.[4]
