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Taxaceae

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Title: Taxaceae  
Author: World Heritage Encyclopedia
Language: English
Subject: Austrotaxus, Pinales, Taxaceae, Taxales, Taxus celebica
Collection: Eocene First Appearances, Pinales Families, Taxaceae
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Taxaceae

Taxaceae
Temporal range:
Middle Eocene - Present 44 mya - 0[1]
Є
O
S
D
C
P
T
J
K
Pg
N
Foliage and mature arils
Scientific classification
Kingdom: Plantae
Division: Pinophyta
Class: Pinopsida
Order: Cupressales[2]
Family: Taxaceae
S.F. Gray
Genera
(5 species)
(1 species)
(11 species)
(1 species)
(about 11 species)
(6 species)

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

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, rarely monoecious. The male cones are 2–5 millimetres (0.079–0.197 in) long, and shed pollen in the early spring. The female cones are highly reduced, with just one ovuliferous scale and one seed. As the seed matures, the ovuliferous scale develops into a fleshy aril partly enclosing the seed. 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]

Classification

Taxaceae is now generally included with all other conifers in the order Pinales, as DNA analysis has shown that the yews are monophyletic with the other families in the Pinales (Chase et al., 1993; Price, 2003), a conclusion supported by micromorphology studies (Anderson & Owens, 2003). 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 taxad in his book ”1916, Conifers and taxads of Japan".[4]

Some studies in the early 2000s suggested the genera Torreya and Amentotaxus were better transferred to Cephalotaxaceae, as genetic tests showed they are were more closely related to Cephalotaxus than to Taxus. More recent studies have included, with Cephalotaxus, in a broader interpretation of Taxaceae as a single larger family (Price, 2003). In this sense, the Taxaceae includes six genera and about 30 species.

The differences suggested between Taxaceae and Cephalotaxaceae were based on the morphology of the seeds, with Taxaceae having smaller mature seeds growing to 5–8 millimetres (0.20–0.31 in) in 6-8 months and not being fully enclosed by the aril. Cephalotaxaceae seeds show a longer maturation period, ranging from 18-20 months, with the mature seeds fully enclosed in the aril and ranging from 12–40 millimetres (0.47–1.57 in).

A few botanists have transferred Austrotaxus to its own family, the Austrotaxaceae, suggesting it may be closer to the Podocarpaceae than to the other Taxaceae, but genetic evidence does not support this transfer.

References

  • Anderson, E. & Owens, J. N. (2003). Analysing the reproductive biology of Taxus: should it be included in Coniferales? Acta Hort. 615: 233-234. (conclusion is 'yes')
  • Chase, M. W. et al. (1993). Phylogenetics of seed plants, an analysis of nucleotide sequences from the plastid gene rbcL. Ann. Missouri Bot. Gard. 80: 528-580.
  • Price, R. A. (2003). Generic and familial relationships of the Taxaceae from rbcL and matK sequence comparisons. Acta Hort. 615: 235-237.

Footnotes

  1. ^ Manchester, S.R. (1994). "Fruits and Seeds of the Middle Eocene Nut Beds Flora, Clarno Formation, Oregon". Palaeontographica Americana 58: 30-31. 
  2. ^ Christenhusz, J. M. M.; Reveal, J. L.; Martin, F. G.; Robert, R. M.; Chase, W. M. (2011). "Linear sequence, classification, synonymy, and bibliography of vascular plants: Lycophytes, ferns, gymnosperms and angiosperms" (PDF). Phytotaxa 19: 1–134. 
  3. ^ Yew Poisoning: MedLine Plus Medical Encyclopedia
  4. ^ taxad (plant family) : see Taxaceae; britannica


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