Conifers Garden - Online Tree Nursery

Cedrus

Cedar  Trew
Pinaceae

 

Evergreen trees with a straight single trunk bearing numerous, spirally arranged horizontal branches. Lower branches sometimes turning up and becoming massive and trunklike. Bark smooth at first, nonfibrous, flaking in scales, cracking to pass through a more or less checkerboard pattern, and then becoming deeply ridged and furrowed with age. Crown conical when young, broadening and flattening markedly with age, often spreading wider than high. Branchlets of two kinds: outstretched long shoots and permanently condensed short shoots. Long shoots extending the growth of the tree, minutely hairy at first, slightly ribbed from the attached, peglike leaf bases. Short shoots bearing most of the foliage and the cones, ringed with alternating groups of leaf scars and persistent bud scales. Winter buds well developed but small, scaly. Leaves spirally arranged and radiating all around the twigs, widely spaced on long shoots, crowded in a ring on short shoots. Leaf blade needlelike, three- ot four-sided in cross section, wider than thick, straight stiff, the tip pointed, the base narrowed to its joint with the raised peg on the twig.

Plants monoecious or partially dioecious. Pollen cones single at the tips of short shoots, upright, with numerous, densely spirally arranged pollen scales. Each scale bearing two somewhat egg-shaped pollen sacs attached along the stalk. Pollen grains large (body 24-80 µm long), with two round, wrinkly air bladders that blend smoothly into the unusually thick cap of the oblong, minutely bumpy body. Seed cones barrel-shaped or cylindrical, single at the tips of short shoots, upright from pollination through to maturity, maturing in two or three seasons. Cones breaking up at maturity to shed both the seeds and the tightly packed, densely spirally arranged, woody seed scales, leaving behind a narrowly conical, long-persistent cone stalk. Seed scales wedge-shaped beyond a narrower stalk, the tiny, hidden bract attached only at the base. Seeds two per scale, the body and the much larger, asymmetrical wing each roughly triangular. Seed wing derived from the skin of the seed scale and covering it, cupping the seed body on one side and wrapping around it a little on the other side. Cotyledons 6-10, each with one vein. Chromosome base number x = 12.

Wood soft, medium weight, light brown, the heartwood sweetly and sharply fragrant, decay resistant. Growth rings well defined, marked by inconspicuous latewood. Vertical resin canals absent but developing resin canals in the rays in response to wounding.

Each face of the needles with a narrow stomatal band. Individual stomates slightly sunken in a shallow pit, the four to six surrounding subsidiary cells, smooth, often shared between adjacent stomates in (but not between) a row, sometimes with a partial second circle along the sides only, and without a Florin ring. Leaf cross section with one resin canal on each side near the lower epidermis more than halfway out from the two-stranded midvein to the outer corner. Midvein accompanied on its lower side by transfusion and sclerenchyma tissue, the whole surrounded by a conspicuous cylinder of endodermis. Photosynthetic tissue with cells more or less radially aligned out from the midrib, the outermost layer not always forming a definite, dense palisade inside the epidermis and adjoining, nearly continuous hypodermis.

The aromatic wood of the true cedars has given these trees their social importance since ancient times and has also contributed to the ambiguities surrounding them. Although they are referred to here as the “true” cedars, the Greek name kedros (from which the Latin common name for the trees, Cedrus is derived) was also applied to eastern Mediterranean junipers with equally fragrant wood, just as the name cedar is applied today to a number of other members of the family Cupressaceae unrelated to Cedrus and the Pinaceae. In fact, the name Cedrus was first formally applied in botanical nomenclature in 1755 to a genus of Cupressaceae, 2 years before Trew used it to give Linnaeus’s Pinus cedrus its own genus. However, the present usage was preserved by formally conserving the name, with the cedar of Lebanon (Cedrus libani) as the type, against the competing usage by Duhamel.

Members of the genus have been appreciated and cultivated in their native countries for centuries and are now grown worldwide in suitable climates. Cultivar selection has been fairly extensive, favoring foliage color (especially blue and golden variants) and growth habit (including many dwarf and weeping cultivars). Both the number of species of true cedar and the position of the genus within the family Pinaceae are controversial. Many features of structure, leaf pigments, and immunological reactions place Cedrus among the abietoid genera, with a particularly close resemblance to the true firs (Abies), which have the most similar seed cones to those of Cedrus. DNA studies, in contrast, are inconsistent in their placement of Cedrus and its relationship to Abies. These studies often suggest that Cedrus is an early branch of the abietoid group, or even an early branch of the whole family, and not closely related to any other genus. The isolated position of the cedars among the Pinaceae is reinforced by a number of unusual characteristics, including maturation of pollen cones and pollination in the autumn rather than in the spring as in other Pinaceae. The chemistry of the fragrant wood is also distinctive within the family in lacking the resin acids found in many other Pinaceae and replacing them with unusual oil compounds not found elsewhere.

The geologically recently separated regional populations of true cedars are variously treated by different botanists as distinct species, subspecies, or varieties. The close relationship among these populations emphasized by strongly overlapping or nearly identical characteristics for traits that usually vary among species within other genera of Pinaceae. For instance, while most genera of Pinaceae have species with distinctive microscopic sculpturing on the inner side of the protective cuticle layer covering the epidermis, the cedars cannot be told apart on basis. The Himalayan cedar (Cedrus deodara) is the most distinct population, and almost all botanists accept it as an independent species. This is not the case with the populations in the Mediterranean region, traditionally assigned to either two or three species, primarily by where the trees come from. These morphologically intergrading, if geographically separated, regional populations are treated here as subspecies of a single species. Given the lack of clear morphological distinctions among them, treating these cedars as separate species would only be justifiable if they were reproductively isolated from one another, and there is presently no available systematic information about this.

The fossil record is also ambiguous about the antiquity and position of the true cedars. Pollen grains resembling those of Cedrus are found as early as the Jurassic, some 150 million years ago, and are widespread in the northern hemisphere, including North America. It is not clear that these fossils really belong to Cedrus, however, and identifiable needles, seeds, and cone scales are much later and much more restricted, being confined to western Eurasia from about the Oligocene, some 25 million years ago. True cedars were common in Europe throughout the Tertiary from then on but became restricted to southern Europe early in the Pleistocene ice ages and were finally eliminated from the continent. At some times during the Pleistocene, Cedrus spread across the Sahara in response to cooler, moister conditions. The western Himalayan portion of the range of the genus dates back at least to the late Pliocene, about 2 million years ago. Thus the present fragmented distribution of Cedrus is geologically very recent, a product of the Pleistocene glacial cycles.

 

References

  • Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
  • Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
  • IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.


 

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