Sequoiadendron
Giant sequoia, (Lindley) J. Buchholz 1939
Cupressaceae
Sequoiadendron - Giant sequoia description
Giant evergreen trees with thick, deeply furrowed, fibrous bark clothing the massive trunk. Crown cylindrical to narrowly dome-shaped, made up of relatively few massive limbs, typically turning up with elbowlike bends, the individual limbs as large as mature whole trees of many other conifers. Branchlets poorly differentiated into long and short shoots, densely clothed with leaves. Branched clusters of short shoots borne on a framework of permanent long shoots with slightly greater internodal elongation, falling intact after several years. Without definite winter buds. Leaves densely spirally arranged, awl-shaped to scalelike, the free tip spreading and longer than the attached base in young trees but gradually reduced and pressed forward with maturity.
Plants monoecious. Pollen cones unstalked, single at the ends of short shoots, spherical to oblong, with 12-20 spirally arranged pollen scales, each with two to five pollen sacs. Pollen grains small to medium (25-45 µm in diameter), flattened spherical with a pronounced germination papilla but otherwise almost featureless. Seed cones single at the ends of short shoots, maturing in their second year, remaining intact at maturity and persisting several years. Each cone oblong, woody, with 25-44 shieldlike seed scales. Each scale with the fertile portion and bract about equal and intimately fused to form a horizontally diamond-shaped external face bearing a triangular central protrusion from a horizontal groove. Seeds (3-)9-13 per seed scale in two rows, lens-shaped, with two equal wings derived from the seed coat along the whole length of and slightly wider than the body. Cotyledons usually three or four, each with one vein. Chromosome base number x = 11.
Wood odorless, light, weak, and brittle but very decay resistant, with a proportionately narrow band (of up to some 200 growth rings!) of almost white to very pale yellowish brown sapwood sharply contrasting with the red to purplish brown or dark brown, sometimes somewhat streaky heartwood. Grain very fine and even, with well-defined but somewhat waxy growth rings marked by an abrupt transition to a fairly narrow band of darker, smaller, thicker-walled latewood tracheids. Resin canals absent but with numerous individual resin parenchyma cells scattered primarily through the earlywood.
Stomates in irregular lines aggregated into two narrow bands on the inner face and bands or patches on the outer face, especially near the base. Each stomate sunken beneath and often almost hidden by the one to three concentric full or partial rings of four to six surrounding subsidiary cells that lack a Florin ring. Leaf cross section with a central, single-stranded midvein above a single small resin canal and flanked by wedges of transfusion tissue. Photosynthetic tissue with a poorly organized palisade layer (and scarcely identifiable as such) all the way around the leaf inside the epidermis and adjacent, very discontinuous, thin hypodermal layer reinforcing the corners.
One species in California. Buchholz used the name Sequoiadendron (hybrid Greek for “Sequoia tree”) to preserve the traditional association of the giant sequoia with the redwood genus from which he had segregated it. The separation of Sequoiadendron from Sequoia, while almost universally accepted today, was quite controversial when first proposed in 1939 and was greeted with intense resistance. Sequoiadendron is more primitive than Sequoia in most respects and has additional similarities to many other genera of Cupressaceae. Nonetheless, DNA similarities and chromosome structures confirm the close relationship of Sequoiadendron to Sequoia and Metasequoia, and their morphology overlaps in a variety of details, though not enough to justify merging them all under Sequoia, as has been suggested.
Because of its rather generalized morphology, the fossil record of Sequoiadendron is not entirely clear but appears to extend back to the Cretaceous in Europe and North America, without representation in Asia. Despite the apparent absence from Asia, however, additional specimens were reported from late Cretaceous sediments in New Zealand, although there are no other southern hemisphere records of the genus from that time to the present. There are several other described genera of sequoioid cones from the Cretaceous of the northern hemisphere, and their relationship to each other and to the three extant genera of the group have yet to be worked out. Giant sequoia (Sequoiadendron giganteum), the sole living species, has been in cultivation since the late 19th century, but it has not been exceptionally variable in cultivation and few cultivars have been named. These include dwarf and weeping forms as well as those with variegated or unusually bluish foliage.
Species:
Attribution from: Conifers Garden