White-berry yew, W.C. Cheng  1947
Taxaceae

Pseudotaxus - White-berry yew description

Evergreen shrubs. Trunks usually several from the base, slender, often contorted and branching repeatedly from near the base. Bark fibrous, peeling in thin, narrow strips. Crown dense, dome-shaped, with numerous thin branches bearing single, paired, or clustered branchlets.  Branchlets all elongate, without dinstinction into long and short shoots, hairless, turning brown soon after expanding in the first year, grooved between and completely clothed by the elongate attached leaf bases. Resting buds well developed, small, with specialized hard, brown, triangular bud scales persisting at the base of the annual growth increment. Leaves spirally and evenly attached all along the twigs, secondarily rearranged into two uneven rows extending out on either side by twisting and bending of the petioles. Each leaf needlelike, sword-shaped, straight to strongly curved, flattened top to bottom.

Plants dioecious. Pollen cones in a double row all along the lower side of the current growth increment, each single in the axil of an ordinary foliage leaf. Each pollen cone cryptically compound, with a short axis bearing three or four crisscross pairs of bud scales at the base above a very short stalk and two additional bracts higher up among the highly reduced simple cones, which consist solely of a stalk with a whorl of four to six pollen sacs at the tip, each thus resembling a single pollen scale with radiating pollen sacs. Pollen grains small (20-35 µm in diameter), nearly spherical with a conspicuous germination papilla and a minutely and fairly evenly bumpy surface but otherwise almost featureless. Seed cones single in axils of and held beneath ordinary foliage leaves. Each seed cone without any trace of seed scales, consisting of six to eight crisscross pairs of outwardly keeled scalelike bracts at the base of a single seed surrounded by but free from a thickly fleshy, white, cup-shaped aril. Seeds plump, hard, slightly flattened, the seed opening straight opposite and pointing away from the stalk, maturing and falling with the aril in a single season. Cotyledons two, each with one vein. Chromosome base number x = 12.

Wood of medium weight and strength, very light brown. Grain fine and even, with well-defined growth rings marked by a broad band of denser latewood. Resin canals and individual resin parenchyma cells both absent, the tracheids (wood cells) with evenly spaced spiral wall thickening, sometimes at a very shallow angle.

Without stomates above and with a broad, waxy white stomatal band on either side of, and clearly broader than, the green midrib region and flanked in turn by a narrower green marginal zone. Each stomatal band consisting of 15-20 closely spaced, straight to wavering, intermittently interrupted lines of stomates. Each stomata aligned lengthwise in its row, shallowly sunken beneath and partially hidden by the four to six surrounding subsidiary cells, of which the end ones are often shared between adjacent stomates in a line, without a Florin ring, the other epidermal cells (in contrast to Taxus) also generally lacking papillae, except right along the edge of the leaf. Midvein single, prominent, narrowly and sharply raised above, broadly and shallowly raised beneath, without resin canals, flanked by cylinders of transfusion tissue. Photosynthetic tissue forming a double palisade layer covering the upper side of the leaves beneath the upper epidermis, which is not accompanied by hypodermis, the palisade giving way to looser spongy mesophyll throughout the remainder of the leaf down to the stomatal region.

One species in eastern China south of the Changjiang (Yangtze River). As might be expected from the name (Greek and Latin for “false yew”), Pseudotaxus is the closest relative to the true yews (Taxus) and, except for the white aril and without detailed examination, is superficially identical to them. The sole extant species of Pseudotaxus, in fact, was originally described as a species of Taxus in 1934, 13 years before it was nearly simultaneously independently transferred to a previously unrecognized new genus by both Cheng and Florin, who used different names, Cheng’s being the earlier by less than 3 months.

Despite their similarities, the generic separation of Pseudotaxus from Taxus is reinforced by the many small features that differ from those in all species of yews, including paired (rather than single) bracts at the base of the pollen and seed cones, the presence of two bracts among the pollen stalks, differences in pollen structure, quickly browning twigs, and waxy white (rather than pale yellowish green) stomatal bands without papillae on the cell surfaces (except at the leaf edge). DNA studies confirm both the close relationship to and the generic separation from Taxus species. These two genera are sister taxa, and their closest relative is the much more distinct New Caledonian yew (Austrotaxus). Pseudotaxus chienii is barely in cultivation, and there has been no cultivar selection. There is no known fossil record for Pseudotaxus, although it might be possible to recognize the relatively distinctive pollen grains of the genus if they were ever found in Tertiary deposits.

References

• Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
• Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
• IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.