Japanese umbrella pine, (Thunberg) P. Siebold & Zuccarini  1842
Siadopityaceae

Sciadopitys - Japanese umbrella pine description

Evergreen tree with fibrous, smoothish bark, peeling in narrow strips on the single trunk. Branches short, slender, densely arranged, sweeping gently upward, often initially in whorls of three to five above a whorl of needles. Branchlets with a swollen portion at the tip of each growth increment showing little internodal elongation and a variable-length, thinner portion beneath with extensive internodal elongation, each twig thus resembling both a short shoot and a long shoot in different portions, grooved between the attached leaf bases, hairless, green at first, becoming brown within the first year. Leaves spirally arranged, of two types: brown scale leaves scattered along the twigs and in two or three close, dense, pseudowhorls at the end of each growth increment; and radiating, linear, photosynthetic, double needles in the axils of the whorled scale leaves (hence the scientific name, Greek for “umbrella pine”). The needle leaves are conventionally interpreted as a pinelike dwarf shoot in which two needles have become fused side to side, the compound origin reflected in two widely separated, complete vascular bundles and a median groove both above and below.

Plants monoecious. Pollen cones in a dense, spherical cluster of 20-30 in the axils of scale leaves at the tip of a branchlet just above a whorl of double needles. Individual cones with numerous spirally arranged pollen scales, each scale with two pollen sacs. Pollen grains small to medium (30-40 µm in diameter), spherical, completely covered with rounded bumps, except at the thin, round, germination pore, this sometimes within a furrow. Seed cones woody, single at the tips of twigs, replacing an annual vegetative increment, maturing and opening in their second season. Individual cones with 50-85 overlapping, spirally arranged seed scales (of which the middle 30-60 are fertile). Each cone scale diamond-shaped externally, with the bract partially overlapping with and fused to the larger fertile portion for about half its length, the fertile portion bearing five to nine seeds in single, angled row. Seeds elliptical, flattened, with lateral wings derived from the seed coat slightly narrower than the seed body but exceeding it in length. Cotyledons two, with one vein. Chromosome base number x = 10.

Wood sharply fragrant, light and soft, moderately decay resistant, the whitish sapwood only weakly distinguished from the light brown heartwood. Grain very even and fairly fine, with obvious growth rings set off by an  abrupt transition to a variably narrow band of much smaller, thicker-walled latewood tracheids. Resin canals and individual resin parenchyma cells both absent.

Lower groove unique among living conifers in having a single stomatal band. Individual stomates only a little lowered beneath the level of the (four to) six eight surrounding subsidiary cells, which bear prominent, rodlike papillae that may partially over-arch the opening. Midveins tilted away from each other, surrounded by transfusion tissue, but mostly extending in wedges out to the sides. Each needle with a pair of resin canals at the lower, outer corners and with none to eight additional canals spaced around the rest of the periphery. Photosynthetic tissue with a single palisade layer all around the needle on both faces (but much thinner and interrupted beneath by the stomatal band) inside the epidermis and single extra layer of hypodermis.

One species in Japan. The plant was first introduced to Europe by John Gould Veitch in September 1860.  In modern times, Sciadopitys was typically aligned with the redwoods, which it broadly resembles in seed cone structure. However, even when included in the family Cupressaceae (or the former Taxodiaceae), because of the very distinctive leaves and growth pattern, it was often given a separate subfamily, equivalent to all other members of the family. Now, the weight of evidence from cone development, chromosomes, paleobotany, and DNA strongly supports assigning it to its own family. This evidence shows that it belongs to the group of families including Cupressaceae and Taxaceae but that it is sister to both and is no more closely related to one than it is to the other.

The nature of the double needles has also been controversial. Besides the conventional interpretation as a pair of needles fused side to side, they were considered to consist predominantly of highly modified stem tissue, which really does not explain their separate vascular bundles. Under either interpretation, they are technically referred to as cladodes, shoots that function like leaves. They have to be shoots because, like the seed scales of conifer cones, they are in the axils of leaves (scale leaves and bracts, respectively, for these two structures). Thus they are also technically short shoots, homologous to those of Pinus, but for ordinary communication it seems less confusing to refer to them as double needles, or even just needles, which they very closely resemble in structure, rather than as short shoots. Developmentally, they arise as a pair of primordia (embryonic leaves) on the bud apex in the axil of a scale leaf, followed by intercalary growth beneath those primordia, rather than by continued growth of the primordia themselves. Thus, even if they did evolve from a pair of leaves, they do not now grow by simple side-to-side fusion but by expansion of a region that is neither quite leaf nor stem in origin. This is a rather common theme in examining plant structures that are considered to represent evolutionary fusions of originally separate structures, like the bract and seed scale that make up many conifer cone scales, or the tubular corolla (petals) of a petunia flower.

Fossil leaves, cones, and pollen of Sciadopitys are found from the late Cretaceous through the Tertiary in the northern hemisphere. Similar leaves, with a single median band of stomata, are common in mid-Jurassic to early Cretaceous sediments of the arctic and were used to support an earlier occurrence of the family, because such leaves are not found in any other living conifer. Careful studies of their structure show that they are simple leaves, unlike the double needles of Sciadopitys, and they are now assigned to an extinct family, Miroviaceae, of uncertain relationship to other conifers. Sciadopitys verticillata has been grown in gardens for centuries in Japan, but few cultivars have been selected. Still, those few include dwarf globes, weepers, and narrow, upright cones and cylinders as well as yellow needles and ones that remain green in winter, when they typically bronze.

Species:

Attribution from: Conifers Garden