Redwood, Endlicher  1847
Cuprassaceae

Sequoia - Redwood description

Giant evergreen trees with a single, straight trunk bearing thick, deeply furrowed, fibrous bark. Branchlets weakly differentiated into long and short shoots, both elongate and clothed with dense or well-separated leaves, but short shoots having just a single year’s growth without further extension in later years and in branched clusters falling intact after several years. Annual growth terminating in loose, scaly, winter buds. Leaves spirally arranged, the attached bases clothing the twigs, of two intergrading types in adult plants: flattened needlelike leaves and scale leaves. Scale leaves borne at both ends of each growth increment, on upright twigs, and on twigs ending in seed cones. Needle leaves longest in the middle portion of each twig, narrowing abruptly to a point at the tip, and having the petiole twisted to bring the needles into a flattened row on either side of the twig.

Plants monoecious. Pollen cones single at the tips of ordinary twigs and of very short reproductive shoots in leaf axils near the tips of the twigs. Individual cones with 6-15 spirally arranged pollen scales, each scale with two to six pollen sacs. Pollen grains small (30-40 µm in diameter), spherical, with a small germination papilla but otherwise almost featureless. Seed cones single at the tips of very short reproductive shoots at or near the ends of foliage twigs, maturing and opening in the first season, oblong or nearly spherical, with 15-30 spirally arranged, shieldlike seed scales. Each scale with (two to) five to seven seeds in one row (or with two additional seeds in a partial second row). Seeds flattened, the body oval and lens-shaped with two wings derived from the seed coat running along both sides of and narrower than the seed body. Cotyledons usually two, each with one vein. Chromosome base number x = 33 (in three sets of 11).

Wood essentially odorless, light, soft, and brittle, but extremely decay resistant, with a narrow band of white to light brown sapwood sharply contrasting with the red to purplish brown or dark brown heartwood. Grain very even to somewhat uneven and fine to moderately coarse, often attractively figured, with obvious growth rings of quite varied widths (including irregular and false rings), marked by a somewhat gradual to abrupt transition to a narrow band of much smaller, thicker-walled latewood tracheids. Resin canals absent but with numerous individual resin parenchyma cells scattered primarily through the outer half of the growth increment, including the latewood.

Stomates of needle leaves in a few irregular lines on both sides of the upper surface and in more lines collected in two bands beneath. Each stomate sunken beneath and partially hidden by the two (or three) circles of four to six surrounding subsidiary cells, which may rise in a low Florin ring around the opening. Leaf cross section with a single-stranded midvein flanked by small wedges of transfusion tissue above a large resin canal and with two additional resin canals above the lower epidermis out near the outer corners of the blade. Photosynthetic tissue forming a somewhat irregular palisade layer beneath the upper epidermis and accompanying incomplete layer of hypodermis and either grading into or giving way abruptly to the spongy mesophyll that extends down to the stomatal bands and lower epidermis, which lacks an adjacent hypodermal layer.

One species along the Pacific Coast of the southwestern United States. The name of the genus is generally thought to honor Sequoyah (c. 1765 - 1843), inventor of the Cherokee syllabary, who died just 4 years before its description, but Endlicher, who described the genus, did not explain his choice of name. Sequoia sempervirens is fairy tender but is widely cultivated in mild, moist temperate regions. Few cultivars have been selected, but those include variations in habit (such as dwarf, compact, and weeping) and foliage from (persistently juvenile) and color (including blue and variegated).

Traditionally included in the family Taxodiaceae since 1926 and lending its common name to that family as “the redwood family,” my suggestion in 1976 that this family be merged into an enlarged Cupressaceae has been supported by several subsequent studies, including comparison of DNA structures. Sequoia, Sequoiadendron, and Metasequoia are closely related, and a few authors treat all three living redwoods as species of Sequoia. The suggestion, made soon after the discovery of Metasequoia, that the dawn redwood is one of the ancestors of coast redwood, is not borne out by detailed analysis of the chromosomes nor by DNA studies.

Sequoia has rather generalized leaves and shoots that also resemble those of various Podocarpaceae and Taxaceae. As a result, many similar fossil shoots from the Triassic and Jurassic once assigned to Sequoia are now considered not to be referable to the redwood. The oldest fossils reasonably securely recognizable as redwoods date from the Cretaceous, like those of most related genera. The discovery of Metasequoia made paleobotanists realize that many of the Cretaceous and Tertiary fossils, especially those of northern lands described as species of Sequoia really belong to Metasequoia or Taxodium. Nonetheless, the genus was widespread at midlatitudes in Eurasia and North America during the Tertiary and did not finally disappear from Europe and Japan until after the Pliocene. Specimens from the Pliocene of Japan were already hexaploids (with six sets of chromosomes), so we do not know when the increase in chromosome number from the typical diploid condition of other Cupressaceae occurred.

Species:

Attribution from: Conifers Garden