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Taxaceae (), commonly called the yew family, is a
conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ext ...
ous
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
which includes six extant and two extinct genera, and about 30 species of
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...
s, or in older interpretations three genera and 7 to 12 species.


Description

They are many-branched, small
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
s and
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from tree ...
s. The leaves are
evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...
, 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 Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is ...
. The catkin like male cones are 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. 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. The mature aril is brightly coloured, soft, juicy and sweet, and is eaten by
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s which then disperse the hard seed undamaged in their droppings. However, the seeds are highly poisonous to humans, containing the poisons taxine and taxol.


Distribution

Species are mostly found in the tropics and the southern temperate zones. There are only a few species in the northern 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, a conclusion supported by micromorphology studies. Formerly they were often treated as distinct from other conifers by placing them in a separate order Taxales.
Ernest Henry Wilson Ernest Henry "Chinese" Wilson (15 February 1876 – 15 October 1930), better known as E. H. Wilson, was a notable British plant collector and explorer who introduced a large range of about 2000 Asian plant species to the West; some sixty bear ...
referred to Taxaceae as "taxads" in his 1916 book. Taxaceae is thought to be the sister group to Cupressaceae, from which it diverged during the early-mid
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
. The clade comprising both is sister to
Sciadopityaceae ''Sciadopitys verticillata'', the or Japanese umbrella-pine, is a unique conifer endemic to Japan. It is the sole member of the family Sciadopityaceae and genus ''Sciadopitys'', a living fossil with no close relatives. The oldest fossils of ...
, which diverged from them during the early-mid
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...
. The oldest confirmed member of Taxaceae is '' Palaeotaxus rediviva'' from the earliest
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
( Hettangian) of Sweden. Fossils belonging to the living genus ''
Amentotaxus ''Amentotaxus'' is a genus of conifers (catkin-yews) comprising five species, treated in either the Cephalotaxaceae, or in the Taxaceae when that family is considered in a broad sense. The genus is endemic to subtropical Southeast Asia, from ...
'' from the Middle Jurassic of China indicate that Taxaceae had already substantially diversified during the Jurassic. 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 Cephalotaxaceae is a small grouping of conifers, that included one to three genera closely allied to Taxaceae. However, members of Cephalotaxaceae are now included in Taxaceae by botanists, instead of as a distinct family, based on phylogenetic e ...
. 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 (e.g.,), was based on relatively minor morphological details: Taxaceae (excluding ''Cephalotaxus'') 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 (from 18–20 months), 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 to recognize ''Cephalotaxus'' (or other genera in Taxaceae) as a distinct family,.


Phylogeny

Phylogeny of Taxaceae.


Extant genera


Footnotes

{{Taxonbar, from=Q223751 Pinales families Extant Eocene first appearances