Taxus brevifolia

Taxus brevifolia
Taxus brevifolia (Pacific Yew) foliage and fruit
Scientific classification
Kingdom: Plantae
Phylum: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Taxaceae
Genus: Taxus
Species: T. brevifolia
Binomial name
Taxus brevifolia
Nutt.
Natural range
Synonyms[1][2]
  • Taxus baccata subsp. brevifolia (Nutt.) Pilg.
  • Taxus baccata var. brevifolia (Nutt.) Koehne
  • Taxus baccata var. canadensis Benth.
  • Taxus boursieri Carrière
  • Taxus brevifolia var. polychaeta Spjut
  • Taxus brevifolia subsp. polychaeta (Spjut) Silba
  • Taxus brevifolia var. reptaneta Spjut
  • Taxus brevifolia subsp. reptaneta (Spjut) Silba
  • Taxus lindleyana A. Murray bis
  • Taxus occidentalis Nutt.

Taxus brevifolia, the Pacific yew[3] or western yew, is a conifer native to the Pacific Northwest of North America. It ranges from southernmost Alaska south to central California, mostly in the Pacific Coast Ranges, but with isolated disjunct populations in southeast British Columbia (most notably occurring on Zuckerberg Island near Castlegar) and in north to central Idaho.[4][5][6][7][8][9]

Characteristics

The Pacific yew is a small to medium-sized evergreen tree, growing 10–15 m tall and with a trunk up to 50 cm diameter, rarely more. In some instances, trees with heights in excess of 20 m 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 rings 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.

It has thin scaly brown bark, covering a thin layer of off-white sap wood with a darker heartwood that varies in color from brown to a magenta/purplish hue. The leaves are lanceolate, flat, dark green, 1–3 cm long and 2–3 mm 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.

The seed cones are highly modified, each cone containing a single seed 4–7 mm long partly surrounded by a modified scale which develops into a soft, bright red berry-like structure called an aril, 8–15 mm 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 by thrushes and other birds, 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 diameter, and shed their pollen in early spring. It is mostly dioecious, but occasional individuals can be variably monoecious, or change sex with time.

Habitat

Pacific yew 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.[4] Pacific yew is shade tolerant; however it can also grow in sun.[10] 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.[11]

Varieties of Pacific yew (Taxus brevifolia)

Taxus brevifolia var. reptaneta. Although T. brevifolia is typically a tree as described above, T. brevifolia var. reptaneta is a shrub variety that generally occurs in the mid to upper elevation range of the typical variety, 3,500 to 4,000 ft (1000–1219 m) at its southernmost occurrence in the Klamath Mountains region, and at lower elevations further north.[12] 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.[13] The epithet reptaneta is from the Latin reptans which means “creeping, prostrate, and rooting,”[14] 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.[12] 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.

Taxus brevifolia var. reptaneta has been arbitrarily indicated synonymous with typical yew, T. brevifolia (var. brevifolia); there are no studies to support this view. Even though the two varieties may be genetically distinct, some botanists recognize species or varieties only if they have different geographically ranges. For example, T. mairei var. speciosa, which occurs with the typical variety in southern China in 10 of 13 provinces, was rejected because “there is no geographic reason” for recognizing it[15] even though it appears genetically distinct.[16]

Taxus brevifolia var. reptaneta has also been proposed to be elevated to subspecies status without justification or explanation. Such a change would likely cause considerable confusion in view of the subspecies rank having already been used in the genus Taxus for defining geographically separated subspecies of a single species (T. baccata).[17] Further, it has been recommended that taxonomists be strongly discouraged from “elevating a ‘variety’ to a ‘subspecies’ unless there is sufficient scientific evidence to warrant such an elevation,” and that “it is crucial to provide continuity.”[18]

Taxus brevifolia var. polychaeta. Typical Taxus 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.[19] However, Taxus brevifolia var. polychaeta differs from var. brevifolia in producing a relatively longer primary shoot[12] with as many five secondary shoots.[20] 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.[12][21]

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 the genus Taxus for 25 years at the time the varieties were described.[12][22]

Uses

Traditionally, the wood was used by Native Americans to make bows and paddles for canoes, in addition many other items from daily life.[23] The Japanese have also used the wood for decorative purposes.[4]

Members of the Pit River Tribe would sell this plant to the Ukiah.[24]

The Concow tribe calls the tree yōl’-kō (Konkow language)[25]

Discovery of taxol

The chemotherapy drug paclitaxel (taxol), used in breast, ovarian, and lung cancer treatment, is derived from Taxus brevifolia. As it was already becoming scarce when its chemotherapeutic potential was realized, the Pacific yew was never commercially harvested from its habitat at a large scale; the widespread use of the paclitaxel (taxol) was enabled when a semi-synthetic pathway was developed from extracts of cultivated yews of other species. Unlicensed pharmaceutical production use of closely related wild yew species in India and China may be threatening some of those species.[26]

References

  1. ↑ Tropicos
  2. ↑ The Plant List
  3. ↑ "Taxus brevifolia". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 8 December 2015.
  4. 1 2 3 Bolsinger, Charles; Jaramillo, Annabelle (1965). "Pacific Yew".
  5. ↑ Hitchcock, C. H., A.J. Cronquist, F. M. Ownbey & J. W. Thompson. 1969. Vascular Cryptogams, Gymnosperms, and Monocotyledons. 1: 1–914. In C. L. Hitchcock Vascular Plants of the Pacific Northwest. University of Washington Press, Seattle.
  6. ↑ Hultén, E. 1968. Flora Alaska i–xxi, 1–1008. Stanford University Press, Stanford.
  7. ↑ Moss, E. H. 1983. Flora of Alberta (ed. 2) i–xii, 1–687. University of Toronto Press, Toronto.
  8. ↑ Munz, P. A. & D. D. Keck. 1959. California Flora 1–1681. University of California Press, Berkeley.
  9. ↑ Welsh, S. L. 1974. Anderson's Flora of Alaska and Adjacent Parts of Canada i–xvi, 1–724. Brigham Young University Press, Provo.
  10. ↑ Mitchell, A. "Acclimation of Pacific yew (Taxus brevifolia) foliage to sun and shade" (PDF). Tree Physiology. 18.
  11. ↑ Scher, Stanley; Schwarzschild, Bert (1989). "Pacific Yew: a Faculative Riparian Conifer with an Uncertain Future" (PDF).
  12. 1 2 3 4 5 Spjut, R. W. 2007. Taxonomy and nomenclature of Taxus. J. Bot. Res. Inst. Texas 1(1): 203–289.
  13. ↑ Web page, World Botanical Associates, Taxus brevifolia var. reptaneta; http://www.worldbotanical.com/taxus_brevifolia_var_reptaneta.htm. Retrieved 9 Dec 2014
  14. ↑ Stearn, W. T. 1983. Botanical Latin. 3rd ed. David & Charles, London
  15. ↑ Möller M, Gao L-M, Mill RR, Liu J, Zhang D-Q, Poudel RC, Li D-Z, 2013. A multidisciplinary approach reveals hidden taxonomic diversity in the morphologically challenging Taxus wallichiana complex. Taxon 62: 1161–1177.
  16. ↑ Gao L-M, Möller M, Zhang X-M, Hollingsworth ML, Liu J, Mill RR, Gibby M, Li D-Z, 2007. High variation and strong phylogeographic pattern among cpDNA haplotypes in Taxus wallichiana (Taxaceae) in China and North Vietnam. Molec. Ecol. 16: 4684–4698.
  17. ↑ Pilger R, 1903. Taxaceae-Taxoideae—Taxeae. Taxus. In: Das Pflanzenreich IV (Engler A. ed.): 110–116.
  18. ↑ Ellison AM, Davis CC, Calie PJ, Naczi RFC, 2014. Pitcher plants (Sarracenia) provide a 21st-century perspective on infraspecific ranks and interspecific hybrids: A modest proposal for appropriate recognition and usage. Syst. Bot. 39: 939–949.
  19. ↑ Florin R, 1951. Evolution in cordaites and conifers. Acta Horti Berg. 16: 285–388, plate
  20. ↑ Web page, World Botanical Associates, Overview of the genus Taxus, http://www.worldbotanical.com/TAXNA.HTM, retrieved 9 Dec 2014
  21. ↑ Web page, World Botanical Associates, Taxus brevifolia var. polychaeta; http://www.worldbotanical.com/taxus_brevifolia_var_polychaeta.htm; retrieved 9 Dec 2014
  22. ↑ Spjut, R. W. 1977. USDA, ARS Memorandum, July 14]. Taxus brevifolia (Taxaceae) reviewed by GMC (Gudrun M. Christensen). A review of literature on taxonomy, ecology, and geographical distribution of the species, including its description, summary of geographical distribution by state or province, and literature reviewed. Distributed periodically during 1981-1992 by the National Cancer Institute to prospective suppliers, without reference to the author, for solicitations of contract bids on up to 30 tons of bark.
  23. ↑ Hansen, Robert (ed.). "Taxus and Taxol - A Compilation of Research Findings".
  24. ↑ Chestnut, V. K. 1902 Plants Used by the Indians of Mendocino County, California. Contributions from the U.S. National Herbarium 7:295-408. (p. 305)
  25. ↑ Chesnut, Victor King (1902). Plants used by the Indians of Mendocino County, California. Government Printing Office. p. 408. Retrieved 24 August 2012.
  26. ↑ BGCI, ‘Miracle’ Cures Face Extinction, retrieved 2008-07-21

Further reading

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