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. 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 long, and shed pollen in the early spring. The female 'cones' are highly reduced to a single seed. 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. 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.
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, a conclusion supported by studies. 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. The broadly defined Taxaceae 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,,, and morphological differences between them are not substantial. Previous recognition of two distinct families, Taxaceae and Cephalotaxaceae, was based on relatively minor morphological details: Taxaceae has smaller mature seeds growing to in 6–8 months, that are not fully enclosed by the aril; in contrast, Cephalotaxus seeds have a longer maturation period, and larger mature seeds fully enclosed by the aril. However, there are also very clear morphological connections between Cephalotaxus and other members of Taxaceae,, and considered in tandem with the phylogenetic evidence, there is no compelling need torecognizeCephalotaxus as a distinct family,.
