Rare Conifers

Calocedrus

Incense-cedar, W. Kurz  1873
Cupressaceae

 

Evergreen trees with a single straight trunk bearing smooth, scaly bark when young, becoming fibrous, deeply furrowed, and peeling in thin strips with age. Densely branched from the base with short, horizontal or gently ascending branches. Crown remaining narrowly columnar through life or broadening to a dome with age. Branchlets in flattened fernlike sprays held vertically. Without definite winter buds. Seedling leaves in alternating quartets, needlelike, standing out from and well-spaced on the stem, seedling phase generally short-lived, giving rise to adult branchlets by the second year. Adult leaves in alternating pairs that resemble aligned quartets because their bases are so close, scalelike, dense, the bases running down onto the branchlets, the lateral and facial pairs dissimilar, without glands or with inconspicuous glands near the tips of facial leaves.

Plants monoecious. Pollen cones numerous, single at the ends of short lateral branchlets, oblong, with 6-10 alternating pairs of pollen scales. Each scale with three or four round pollen sacs. Pollen grains small (25-40 µm in diameter), nearly spherical, with a minute germination bump, otherwise almost featureless. Seed cones relatively sparse, single at the ends of short side branchlets that may be as long as the cones. Leaves of cone-bearing branchlets tightly crowded, without the elongation of the leaf bases characterizing foliage leaves. Cones maturing in a single season, oblong, with three alternating pairs of scales. Each seed scale bearing a bump just below the tip corresponding to the fused bract portion, only the middle pair fertile, with two ovules on each scale, the inner pair as long as the fertile pair but united as a flat plate between them, the outer pair much smaller. Seed oval, with two very unequal wings derived by outgrowth of the seed coat at the top, the larger, inner wing spreading out to the tip of the seed scale. Cotyledons two, each with one vein. Chromosome base number x = 11.

Wood somewhat fragrant, light, soft and weak but highly decay resistant, with very pale yellowish white sapwood sharply contrasting with pinkish heartwood that browns with age. Grain moderately to very fine and even, with weakly defined to prominent growth rings marked by an abrupt transition to a few rows of much smaller and somewhat thicker walled latewood tracheids. Resin canals absent but with abundant individual resin parenchyma cells scattered throughout the growth increment or concentrated in and near the latewood.

Stomates in elongate bands in the grooves between leaves and on the more protected side of the branchlets and fewer and scattered on the more exposed side. Each stomate sunken beneath the four to six (or seven) subsidiary cells and surrounded by a nearly continuous, bumpy Florin ring. Subsidiary cells and other epidermal cells in the stomatal regions also often bearing additional large, round to elongate papillae. Leaf cross section with a single midvein near the twig in the attached leaf base and scarcely entering the free tip. Midvein accompanied toward the outside of the lateral leaves only or both types by a very large resin canal and flanked by small wings of transfusion tissue. Photosynthetic tissue forming a complete but shallow palisade layer all along the exposed portion of the leaves beneath the epidermis and the adjoining thin hypodermis. Scattered sclereids lie just beneath the palisade layer, and the remainder of the leaf is occupied by the looser photosynthetic spongy mesophyll.

Four species in western North America and eastern Asia.

Although originally placed with southern hemisphere incense cedars in Libocedrus, DNA evidence shows that the northern hemisphere incense cedars are more closely related to Platycladus and Microbiota on the one hand, and to Cupressus and Juniperus on the other, placing them squarely among the northern hemisphere genera. The paddle-shaped seed scales must have evolved independently in the northern and southern incense cedars. The southern hemisphere genera lack the flat plate between the fertile scales that is so prominent in Calocedrus. The arrangement of the leaves is apparent whorls of four leaves of equal length, and the consistently alternate branching are also clear points of distinction for Calocedrus. The fragrant wood that gives them their common name is found much more widely among Cupressaceae than in just genera called incense cedars. Nor are the three species of Calocedrus the only ones that merit the translation of the Greek- and Latin-derived name “beautiful cedars”. The North American Calocedrus decurrens is in general cultivation while the Asian species are largely confined to botanical gardens. A modest number of cultivar selections emphasize dwarf forms and foliage color variants. The fossil record for Calocedrus is modest but extends back to the Oligocene in western North America. This record is based on foliage and cones since pollen is not reliably distinguishable from that of related genera.

 

Species:

Calocedrus formosana

 

Attribution from: Conifers Garden


 

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