Taxaceae Explained

Taxaceae, commonly called the yew family, is a coniferous family which includes six extant and two extinct genera, and about 30 species of plants, or in older interpretations three genera and 7 to 12 species.

Description

They are many-branched, small trees and shrubs. The leaves are evergreen, spirally arranged, often twisted at the base to appear 2-ranked. They are linear to lanceolate, and have pale green or white stomatal bands on the undersides.

The plants are dioecious, or rarely monoecious. The catkin like male cones are 2mm5mm long, and shed pollen in the early spring. They are sometimes externally only slightly differentiated from the branches. The fertile bracts have 2-8 pollen sacs.[1]

The female 'cones' are highly reduced. Only the upper or uppermost bracts are fertile and bear one or rarely two seeds. The ovule usually exceeds the scale, although ovules are sometimes rarely enclosed by it. They may be found on the ends of branches or on the branches. They may grow singly or in tufts or clumps.

As the seed matures, a fleshy aril partly encloses it. The developmental origin of the aril is unclear, but it may represent a fused pair of swollen leaves.[2] The mature aril is brightly coloured, soft, juicy and sweet, and is eaten by birds which then disperse the hard seed undamaged in their droppings. However, the seeds are highly poisonous to humans, containing the poisons taxine and taxol.[3]

Distribution

Species are mostly found in the tropics and temperate zones in the northern temperate. There are only a few species in the southern hemisphere.

Classification

Taxaceae is now generally included with all other conifers in the order Pinales, as DNA analysis has shown that the yews are phylogenetically nested in the Pinales,[4] a conclusion supported by micromorphology studies.[5] Formerly they were often treated as distinct from other conifers by placing them in a separate order Taxales. Ernest Henry Wilson referred to Taxaceae as "taxads" in his 1916 book.[6] Taxaceae is thought to be the sister group to Cupressaceae, from which it diverged during the early-mid Triassic. The clade comprising both is sister to Sciadopityaceae, which diverged from them during the early-mid Permian.[7] The oldest confirmed member of Taxaceae is Palaeotaxus rediviva from the earliest Jurassic (Hettangian) of Sweden. Fossils belonging to the living genus Amentotaxus from the Middle Jurassic of China indicate that Taxaceae had already substantially diversified during the Jurassic.[8]

The broadly defined Taxaceae (including Cephalotaxus) comprises six extant genera and about 30 species overall. Cephalotaxus is now included in Taxaceae, rather than being recognized as the core of its own family, Cephalotaxaceae. Phylogenetic evidence strongly supports a very close relationship between Cephalotaxus and other members of Taxaceae,[9] [10] [11] and morphological differences between them are not substantial. Previous recognition of two distinct families, Taxaceae and Cephalotaxaceae (e.g.,[12]), was based on relatively minor morphological details: Taxaceae (excluding Cephalotaxus) has smaller mature seeds growing to 5mm8mm in 6–8 months, that are not fully enclosed by the aril; in contrast, Cephalotaxus seeds have a longer maturation period (from 18–20 months), and larger mature seeds (12mm40mm) fully enclosed by the aril. However, there are also very clear morphological connections between Cephalotaxus and other members of Taxaceae,[13] [14] and considered in tandem with the phylogenetic evidence, there is no compelling need to recognize Cephalotaxus (or other genera in Taxaceae) as a distinct family,.[9] [10]

Phylogeny

Phylogeny of Taxaceae.[15] [16]

Amentotaxus – Catkin-yew

Austrotaxus – New Caledonia yew

Cephalotaxus – Plum yew

Pseudotaxus – White-berry yew

Taxus – Common yew

Torreya – Nutmeg yew

Notes and References

  1. Book: Phillips, Edwin Percy . The genera of South African flowering plants . Government Printer . 1951 . South Africa.
  2. Dörken . Veit Martin . Nimsch . Hubertus . Rudall . Paula J . Origin of the Taxaceae aril: evolutionary implications of seed-cone teratologies in Pseudotaxus chienii . Annals of Botany . Oxford University Press (OUP) . 123 . 1 . 2018-08-22 . 0305-7364 . 10.1093/aob/mcy150 . 30137225 . 6344100 . 133–143.
  3. https://www.nlm.nih.gov/medlineplus/ency/article/002877.htm Yew Poisoning: MedLine Plus Medical Encyclopedia
  4. Chase . M. W. . Soltis . D. E. . Olmstead . R. G. . Morgan . D. . Les . D. H. . Mishler . B. D. . Duvall . M. R. . Price . R. A. . Hills . H. G. . Qiu . Y.-L. . Kron . K. A. . Rettig . J. H. . Conti . E. . Palmer . J. D. . Manhart . J. R. . Sytsma . K. J. . Michaels . H. J. . Kress . W. J. . Karol . K. G. . Clark . W. D. . Hedren . M. . Gaut . B. S. . Jansen . R. K. . Kim . K.-J. . Wimpee . C. F. . Smith . J. F. . Furnier . G. R. . Strauss . S. H. . Xiang . Q.-Y. . Plunkett . G. M. . Soltis . P. S. . Swensen . S. M. . Williams . S. E. . Gadek . P. A. . Quinn . C. J. . Eguiarte . L. E. . Golenberg . E. . Learn . G. H. . Graham . S. W. . Barrett . S. C. H. . Dayanandan . S. . Albert . V. A. . 2. Phylogenetics of Seed Plants: An Analysis of Nucleotide Sequences from the Plastid Gene rbcL . Annals of the Missouri Botanical Garden . JSTOR . 80 . 3 . 1993 . 0026-6493 . 10.2307/2399846 . 528. 2399846 . 1969.1/179875 . free .
  5. Anderson. E.. Owens. J.N.. 2003. Analyzing the Reproductive Biology of Taxus: Should It be Included in Coniferales?. Acta Horticulturae. International Society for Horticultural Science (ISHS). 615. 233–234. 10.17660/actahortic.2003.615.22. 0567-7572. 2021-06-22. 2022-11-26. https://web.archive.org/web/20221126082249/https://www.actahort.org/books/615/615_22.htm. dead.
  6. Book: Wilson, Ernest Henry . The conifers and taxads of Japan. Issued December 30, 1916. . University Press . Cambridge . 1916 . 10.5962/bhl.title.17457 .
  7. Stull. Gregory W.. Qu. Xiao-Jian. Parins-Fukuchi. Caroline. Yang. Ying-Ying. Yang. Jun-Bo. Yang. Zhi-Yun. Hu. Yi. Ma. Hong. Soltis. Pamela S.. Soltis. Douglas E.. Li. De-Zhu. July 19, 2021. Gene duplications and phylogenomic conflict underlie major pulses of phenotypic evolution in gymnosperms. Nature Plants. en. 7. 8. 1015–1025. 10.1038/s41477-021-00964-4. 34282286 . 236141481 . 2055-0278.
  8. Dong . Chong . Shi . Gongle . Herrera . Fabiany . Wang . Yongdong . Herendeen . Patrick S . Crane . Peter R . 2020-06-18 . Middle–Late Jurassic fossils from northeastern China reveal morphological stasis in the catkin-yew . National Science Review . en . 7 . 11 . 1765–1767 . 10.1093/nsr/nwaa138 . 2095-5138 . 8288717 . 34691509 . free.
  9. Quinn . C. J. . Price . R. A. . Gadek . P. A. . Familial Concepts and Relationships in the Conifer Based on rbcL and matK Sequence Comparisons . Kew Bulletin . JSTOR . 57 . 3 . 2002 . 0075-5974 . 10.2307/4110984 . 513. 4110984 . 83816639 .
  10. Rai . Hardeep S. . Reeves . Patrick A. . Peakall . Rod . Olmstead . Richard G. . Graham . Sean W. . Inference of higher-order conifer relationships from a multi-locus plastid data set. . Botany . Canadian Science Publishing . 86 . 7 . 2008 . 1916-2790 . 10.1139/b08-062 . 658–669. 14007221 .
  11. One thousand plant transcriptomes and the phylogenomics of green plants . Nature . Springer Science and Business Media LLC . 574 . 7780 . 2019 . 0028-0836 . 10.1038/s41586-019-1693-2 . 31645766 . 6872490 . 679–685. One Thousand Plant Transcriptomes Initiative .
  12. Hart. Jeffrey A.. 1987. A cladistic analysis of conifers: preliminary results. Journal of the Arnold Arboretum. 68. 3. 269–307. 10.5962/p.185944 . 43782212. 88860959 . 0004-2625. free.
  13. Doyle . James A. . Annual Review of Ecology and Systematics . Annual Reviews . 29 . 1 . 1998 . 0066-4162 . 10.1146/annurev.ecolsys.29.1.567 . 567–599. Phylogeny of Vascular Plants . 85631751 .
  14. Stützel. Thomas. Röwekamp. Iris. 1999. Female reproductive structures in Taxales. Flora. Elsevier BV. 194. 2. 145–157. 10.1016/s0367-2530(17)30893-9. 0367-2530.
  15. Leslie . Andrew B. . Beaulieu . Jeremy . Holman . Garth . Campbell . Christopher S. . Mei . Wenbin . Raubeson . Linda R. . Mathews . Sarah . et al. . 2018 . An overview of extant conifer evolution from the perspective of the fossil record . American Journal of Botany . 105 . 9 . 1531–1544 . 10.1002/ajb2.1143 . 30157290. free.
  16. Leslie . Andrew B. . et al. . 2018 . ajb21143-sup-0004-AppendixS4 . American Journal of Botany . 105 . 9 . 1531–1544 . 10.1002/ajb2.1143 . 30157290 . 52120430 .
  17. Manchester. S.R.. 1994. Fruits and Seeds of the Middle Eocene Nut Beds Flora, Clarno Formation, Oregon. Palaeontographica Americana. 58. 30–31.

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