The families of gymnosperms


L. Watson and M. J. Dallwitz


Yews, California Nutmeg.

Including Amentotaxaceae, Austrotaxaceae, Torreyaceae.

Vegetative. Evergreen; profusely branching trees and shrubs. Resinous (with Torreya exhibiting a resin canal in the leaf and resin cells in the wood), or not resinous (Taxus and Austrotaxus, except that resin cells have rarely been reported from roots). Main branches spiral, or whorled, or opposite. The leafy branchlets flattened in one plane. The vegetative branch systems without conspicuously specialised short-shoots. Mature leaves more or less linear (often somewhat asymmetric); relatively soft; not clustered; alternate (though often appearing two-ranked on mature shoots). Longitudinal resin canals present in the leaves (in Torreya), or absent from the leaves (mostly, e.g. Taxus); when present, 1 per leaf, this median-abaxial.

Reproductive organization. Usually dioecious. The reproductive organization not flower-like. The ovules solitary, arillate, not in cones; terminating axes (terminating inconspicuous secondary dwarf shoots, as in most yews, or terminating visible dwarf shoots with a few basal scales, as in Taxus canadensis, but uncomplicated by vestiges representing reduced short-shoots of the kind characterizing true conifers); orthotropus; 1 integumented.

The small male cones bearing peltate-symmetric, Equisetum-like sporangiophores with 6–8 pendulous pollen-sacs in Taxus, or dorsiventral scale-like sporophylls with 4 abaxial sacs in Torreya. In Austrotaxus, each sporangiphore is subtended by a bract. Pollen-sacs 2–9 per microsporophyll. Pollen without air bladders (?). Pollination anemophilous, involving a “liquid drop” mechanism.

Seeds and seedlings. Seeds with a fleshy investment; the fleshy investment representing a genuine aril (a secondary outgrowth from the floral axis, which varies somewhat in form among the genera); wingless. Cotyledons 2.

Wood anatomy. Growth rings distinct. Heartwood present and distinctively coloured. Latewood not conspicuous. Wood with a distinct odour (Torreya), or without distinct odour; without distinct taste; not greasy; without dimpled grain. Tracheids with opposite and multiseriate bordered pits; without callitroid pit-border thickenings. Margins of the tori not scalloped. Earlywood tracheids with spiral thickenings. Axial parenchyma present (in Austrotaxus), or absent. Axial parenchyma abundant (in Austrotaxus,), or scarce. Axial parenchyma not zonate. Axial parenchyma with nodular thickenings or bead-like on the transverse or end-walls (in Torreya californica), or without nodular thickenings on the transverse or end-walls. Rays exclusively uniseriate. Ray tracheids absent or very infrequent. Earlywood ray cells with horizontal walls thinner than those of the adjacent vertical tracheids above and below the ray (Austrotaxus), or with walls similar in thickness to those of adjacent vertical tracheids. Latewood ray cells with unpitted horizontal walls, or with pitted horizontal walls. The pitting when present, strong, or weak. Ray cells exhibiting indentures at the corners; without nodular thickenings on their end walls. Ray tissue without crystals. Earlywood cross-field pits cupressoid, or cupressoid and taxodioid (in Austrotaxus). Normal vertical resin ducts absent.

Geography, cytology. Temperate; Northern hemisphere, south to Celebes and Mexico, Austrotaxus in New Caledonia.

Basic chomosome number, n = 12.

Taxonomy. 17 species; Amentotaxus, Austrotaxus, Pseudotaxus, Taxus, Torreya. Order Taxales.

Comments. The organization of female reproductive shoots in Taxaceae correspond with those of the ancestral taxads in their relative morphological simplicity (see above), although some extant forms exhibit aggregations of fertile shoots which may represent a relatively recent development. Taxus baccata has been well known from ancient times for its toxic properties, and has been thoroughly researched in that context. In addition to the alkaloid taxine, it includes hydrocyanic acid and ephedrine as well as an extremely irritant volatile oil, and all parts of the plant (fresh or dried) except the aril are poisonous to humans and livestock. Surprisingly, information on other members of the family in this connection is proving elusive.

Miscellaneous. • Taxus baccata and T. cuspidata (Dallimore and Jackson). • Taxus baccata (Curtis). • Torreya californica, Torreya grandis and Torreya nucifera (Dallimore and Jackson). • Taxus baccata and T. cuspidata: technical details (Sporne). • Female reproductive organization: Taxus, Austrotaxus and Nothotaxus (Florin). • Female reproductive organization: Amentotaxus argotaenia. • Leaf epidermes: Amentotaxus, Nothotaxus, Taxus (Florin). • Wood anatomy: Taxus baccata.

To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2008 onwards. The families of gymnosperms. Version: 9th April 2015.’.