Taxaceae

Taxobox
name = Taxaceae


image_width = 250px
image_caption = "A fleshy aril partly surrounds each seed in the
yews; note also immature cones with seed
not yet surrounded by the aril"
regnum = Plantae
divisio = Pinophyta
classis = Pinopsida
ordo = Pinales
familia = Taxaceae
familia_authority = S.F. Gray
subdivision_ranks = Genera
subdivision = Taxaceae "sensu stricto" "Taxus" "Pseudotaxus" "Austrotaxus" —— Cephalotaxaceae "Torreya" "Amentotaxus" "Cephalotaxus"

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.

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 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 "rbc"L. "Ann. Missouri Bot. Gard." 80: 528-580.
* Price, R. A. (2003). Generic and familial relationships of the Taxaceae from "rbc"L and "mat"K sequence comparisons. "Acta Hort." 615: 235-237.