Тихоокеанский тис и его разновидности

Species of conifer

Taxus brevifolia, the Pacific yew or western yew, is a species of tree in the yew family Taxaceae native to the Pacific Northwest of North America. It is a small evergreen conifer, thriving in moisture and otherwise tending to take the form of a shrub.

A small evergreen conifer (sometimes appearing as a shrub), the Pacific yew grows to tall and with a trunk up to in diameter, rarely more. In some instances, trees with heights in excess of 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 accurate ring counts to determine a specimen's true age. Often damaged by succession of the forest, it usually ends up in a squat, multiple leader form, able to grow new sprouts from decapitated stumps. 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. The epithet reptaneta is from the Latin reptans which means "creeping, prostrate, and rooting", which is exactly what this variety does; in rooting it forms yew thickets; hence, the epithet reptaneta ( 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. though it appears genetically distinct. T. brevifolia var. reptaneta has also been proposed to be elevated to a subspecies, despite that rank being used to define geographically separated groups of T. baccata.

Typical T. 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. T. brevifolia var. polychaeta differs from var. brevifolia in producing a relatively longer primary shoot The epithet, polychaeta, is in reference to the primary shoot resembling a polychaete worm; hence, its common name 'worm cone yew'. Variety polychaeta appears to be relatively rare. It may have been extirpated from the type locality—around Mud Bay near Olympia, Washington—as a result of urban expansion. It is also known from Northern Idaho and Sonoma County, California. 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 of Taxus for 25 years at the time the varieties were described.

Yew foliage is very similar to that of Sequoia sempervirens, the coastal redwood. 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, The tree's shade tolerance allows it to form an understory, which means that it can grow along streams providing shade to maintain water temperature.

Birds eat the fruit cups and spread the seeds. Moose feed on the tree in winter in forests of the Rocky Mountains. The Concow tribe calls the tree yōl’ kō (Konkow language). Modern day longbow makers report that a very small percentage of yew trees are of a grain suitable for their craft. The Japanese have used the wood for decorative purposes, and the Taiwanese have valued it as well. The juicy red cup around the seed seems to be edible (but not the toxic seed within), with a cherry jello like taste. The chemotherapy drug paclitaxel (taxol), used in breast, ovarian, and lung cancer treatment, can be derived from Taxus brevifolia 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.