Conifers Garden US - World's conifers | Shipping Worldwide


Plum yew, P. Siebold & Zuccarini ex Endlicher  1842


Evergreen trees and shrubs, usually with multiple stems from at or near the ground. Trunks cylindrical, eccentric, or sometimes fluted or buttressed. Bark obscurely or evidently fibrous, smooth and flaking in scales or peeling in narrow strips and becoming coarsely furrowed. Crown dense and dome-shaped in shrubs and some trees, open and irregular in others, with slender, gently upwardly angled branches initially in near whorls. Branchlets all elongate, without distinction into long and short shoots, hairless, remaining green for at least the first year, completely clothed by and deeply grooved between the elongate attached leaf bases. Resting buds well developed, with numerous hard brown bud scales persisting on the stem after shoot expansion. Leaves attached in opposite pairs with successive pairs spiraling around the twigs but presented in two flat, drooping, or V-shaped rows by bending and twisting of the petioles. Leaves sword-shaped, straight or slightly curved forward, with nearly parallel sides or tapering gradually toward the tip, flattened top to bottom, sometimes arching around the midrib.

Plants dioecious. Pollen cones in tight, spherical, scaly-stalked, spirally arranged clusters of 5-11 in the axils of leaves all along both sides of and underneath 1-year-old otherwise ordinary foliage shoots. Each pollen cone united with the supporting bract (except the terminal cone of the cluster) and with 1-10(-16) highly reduced pollen scales. Pollen scales each bearing 2-3(-7) by fusion of adjacent scales) egg-shaped, hanging pollen sacs. Pollen grains somewhat irregularly spherical with a low papilla at one end, small (25-35 µm in diameter), without air bladders, minutely and unevenly bumpy over the whole surface. Seed cones single or in groups of two to eight on separate scaly stalks in the axils of scale leaves or foliage leaves at or near the tip of otherwise ordinary 1-year-old shoots. Individual cones very compact, remaining fleshy, with four to eight pairs of fertile bracts, the successive pairs at right angles to one another. Each bract bearing two ovules on a highly reduced, attached seed scale, usually with only one (or two) seeds maturing in a cone. Seeds large, oval, the fleshy outer layer of the seed coat intimately united with a surrounding fleshy aril that extends almost all the way to the tip, maturing in two seasons. Cotyledons two, each with one vein. Chromosome base number x = 12.

Wood hard and heavy, the white to light brown sapwood moderately distinct from the brown heartwood. Grain very fine and even, with almost undetectable to moderately evident growth rings marked by very narrow bands of slightly denser latewood. Resin canals absent but usually with scattered or grouped individual resin cells and tracheids with spiral thickening.

Stomates confined to pale green or white stomatal bands beneath on either side of and at least as wide as the midrib region, each band consisting of 10-25 lines of stomates. Each stomate deeply sunken beneath and tucked under the four to six subsidiary cells, which are sometimes shared between adjacent stomates in a row (but not between rows), sometimes with a partial second circle of subsidiary cells along the sides, and flanked on both sides by a low ridge of cuticle, not quite forming a Florin ring. Midvein single, prominent, raised both above and beneath, with one small resin canal surrounded by two or more layers of wall cells immediately beneath it and wings of transfusion tissue on either side. Photosynthetic tissue with an irregular palisade layer directly beneath the upper epidermis without an intervening hypodermis, the palisade opening up beneath into the looser spongy mesophyll that extends down to the lower epidermis and the stomatal bands.

Eight species in eastern and southern Asia from Japan and Korea to Indochina and eastern India.

The scientific name (Latin for “head yew”) refers to both the seed cones and the pollen cones, both of which are nearly spherical and very compact, constituting a head in botanical terminology. Members of the genus have been cultivated for centuries in eastern Asia and are now in modest general cultivation worldwide in suitable climates. Cultivar selection initially focused on the edible seeds but expanded subsequently to include variations in growth habit (especially fastigiated or spreading forms) and in size (longer or shorter than normal), attitude, and color of foliage (like golden or dark green).

Cephalotaxus is the only genus in the Taxaceae with seed cones that are readily identifiable as such. Because of this, Pilger in 1926 reversed his 1903 inclusion of the genus in Taxaceae and assigned it to separate family all by itself. This separation was further emphasized by Florin in 1948, who kept Cephalotaxus among the conifers when he separated Taxaceae from the other conifers as a distinct order. Placement of Cephalotaxus in a monotypic family away from Taxaceae has been almost universally accepted since then, despite its very strong morphological similarities to other Taxaceae. Except for the supporting (and rather small) cones, the large plumlike seeds are rather similar to those of Amentotaxus and Torreya, as are the leaves. The distinctive leaf arrangement (technically referred to as bijugate) is like that of Amentotaxus, while the arrangement of the pollen cones is like that of Torreya though more complex. The pollen resembles that of Pseudotaxus, and pollen scales similar to those of Taxus, Pseudotaxus, and Amentotaxus, with five or more pollen sacs, are found at the tip of the terminal cone in the pollen cone clusters of Cephalotaxus. Spiral thickening of the wood cells (tracheids) is found in all these genera but is rare elsewhere in the conifers. Confirming these and other morphological, anatomical, and biochemical similarities, DNA studies show quite convincingly that the family Taxaceae, including Cephalotaxus, is a monophyletic group. These studies also show that Cephalotaxus constitutes one of three groups of genera (subfamilies) within the family, the other two being. Amentotaxus and Torreya on the one hand and Austrotaxus, Pseudotaxus, and Taxus on the other. Which two of these subfamilies are most closely related is somewhat ambiguous, although Cephalotaxus may be slightly more distantly related to the other two groups than they are to each other.

The division of Cephalotaxus into species has also been controversial. There has been no modern botanical monograph of the genus since Pilger’s in 1903, and many floras and horticultural accounts recognize as many as 11 species instead of the eight accepted here. Some of the additional proposed species are based on features like the color of the stomatal bands, which varies with the age of the foliage, or the presentation of the leaves, which varies with the amount of shade. Nonetheless, it is possible that some of the extra taxa could be recognized as additional botanical varieties of the eight accepted species. On the other hand, Cephalotaxus harringtonii, Cephalotaxus mannii, and Cephalotaxus sinensis are similar enough to one another that they might be combined as a single species with further evidence. Clearly, more study of this group is needed. Unfortunately, this is becoming increasingly difficult as plum yews become rarer in nature due to direct exploitation of the larger species for wood and indirect damage through habitat destruction.

While Cephalotaxus is now confined to eastern and southern Asia, it was once much more widely distributed. Fossil foliage or seeds, or both, are known from the Eocene to the Pliocene of western North America (roughly 40 million to 4 million years ago) and from the Oligocene to the Pliocene of Europe (about 30 million to 4 million years ago) but are only known to extend back to the Miocene in eastern Asia (about 20 million years ago). However, some much older fossils, dating back to the Jurassic, more than 150 million years ago, share some similarities with Cephalotaxus and may be related to it, although this relationship is not firmly established.





Attribution from: Conifers Garden