The systematics of Taxaceae have not been recognized farther back than the Cretaceous and its family is comparatively a modern one among the gymnosperms. It is possible that older Taxaceae existed and that they have not been recognized among coniferous remains, but there has been a failure to find them earlier than the Cretaceous.
There is evidence to show a common ancestry for the various genera of the Taxaceae and Coniferae, a view which is greatly strengthened by the testimony afforded by the spiral tracheids of Larix Americana, Psuedotuga, and Pinus taeda.
They differ in bearing a single ovule (occasionally two) terminally on a modified shoot. For this reason, including fossil evidence, Taxaceae is sometimes excluded from the Coniferales and is transferred to a separate order - Taxales. The typical needle is a common leaf type and is associated with conifers found on all Pinaceae, Taxaceae, and Cephalotaxaceae. Yews are unusual among the conifers for being either male or female.
Florin suggested that the terminal ovule in Taxaceae is not homologous with the ovules in other conifers, but evolved from an ancestor that ultimately had terminal ovules. Torreya differs from the Taxus (Yews) in its secondary wood in that it contains wood parenchyma, but is otherwise similar.
Taxaceae have been called the oldest living conifers and most recently they have connected with Ginkgo , Cephalotaxus and the Codaitales on account of the structure of the ovuliferous shoot of Taxus .
In Taxaceae, the bordered pits do not in themselves provide very conclusive evidence as to the relative position of the family. Of the eight investigated species, representing three genera, only two variants in pit position occur. Constancy in the structure of such pits has been found to be characteristic of Ginkgo,Taxaceae ,and all other forms of conifers, from which we may conclude that the bordered pit is essentially a primitive character.
Recent studies of 18S rRNA sequences indicate that Taxaceae, Caphalotaxaceae, Cupressaceae, and Taxodiaceae form a monophyletic group. This research also indicates that Amentotaxus is closer to Torreya than to Cephalotaxus, suggesting that Amentotaxus is better classified as a member of Taxaceae.
Chaw, Shu-Miaw; Sung, Huang-Mo; Long, Huei; Zharkikh, Audrey; Li, Wen-Hsiung (1995) The Phlogenetic Positions of the Conifer Genera Amentotaxus, Phyllocladus, and Nageia Inferred from 18S rRNA Sequences. Journal of Molecular Evolution 41:224-230
Coulter, M. John. Morphology of Gymnosperms. The University of Chicago Press: Chicago, Illinois, 1910.
Penhallow, David. A Manual of the North American Gymnosperms. Ginn and Company Publishers: Boston, 1907.
Sporne, K.R. The Morphology of Gymnosperms-The structure and evolution of primitive seed plants. Hutchinson University Library: London, 1965.
