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 A fleshy aril partly surrounds each seed in the
yews; note also immature cones with seed not yet surrounded by the aril |
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Taxaceae sensu stricto |
The family Taxaceae, commonly called the yew family, includes three genera and about 7 to 12 species of coniferous plants, or in other interpretations (see Classification, below), six genera and about 30 species.
They are much 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 mm 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.
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Classification
The 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.
The genera Torreya and Amentotaxus, previously included in this family, are better transferred to the Cephalotaxaceae, as genetic tests show they are more closely related to Cephalotaxus than to Taxus. Alternatively, they may be 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 between the Taxaceae and the Cephalotaxaceae are as follows:
| Family | Taxaceae | Cephalotaxaceae |
|---|---|---|
| Cone aril | partly encloses seed | fully encloses seed |
| Cone maturation | 6-8 months | 18-20 months |
| Mature seed length | 5-8 mm * | 12-40 mm |
* To 25 mm in Austrotaxus
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.
Others
- Ernest Henry Wilson called Taxaceae as taxad in his book ”1916, Conifers and taxads of Japan"1
Footnotes
- ^ taxad (plant family) : see Taxaceae; britannica
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Wikipedia content modification information:
- This page was last modified on 1 December 2008, at 18:41.
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