Incense cedar, Endlicher  1847
Cupressaceae

Libocedrus - Incense cedar description

Evergreen trees and shrubs with a single, straight trunk clothed in fibrous, furrowed bark peeling in long vertical strips. Densely branched from the base with short, horizontal or upsweeping branches forming a conical crown. Branchlets usually in flattened, fernlike sprays with opposite or alternate branching only from the lateral leaf pairs, but sometimes in more three-dimensional arrangements of branchlets that are squarish in cross section. Without definite winter buds. Seedling leaves in alternating quartets, needlelike, standing out from and well-spaced on the stem, seedling phase short-lived, juvenile side branchlets appearing by the second year. Juvenile and adult leaves in alternating pairs, scalelike, dense, the bases running down a little onto the branchlets, the alternate pairs either all alike or differentiated into lateral and facial pairs. Lateral leaves of juveniles usually larger and more spreading than those of adults, generally keeled and folded around the branchlet, at least at the base. Facial leaves more or less oval, the successive pairs just overlapping or well separated by the lateral pairs. Leaves without glands.

Plants monoecious or dioecious. Pollen cones numerous but single at the tips of branchlets, oblong, with 5-12 alternating pairs of pollen scales, each scale with a heart-shaped blade bearing three to six pollen sacs at the base, around the short stalk. Pollen grains small (20-40 µm in diameter), nearly spherical, minutely bumpy and with an ill-defined, minute germination pore or slight projection. Seed cones typically in two to four pairs at the base of vigorous lateral shoots, each single at the end of a short branchlet, oblong, maturing in a single season. Cone with two obvious alternating pairs of thin woody scales and five smaller pairs grading into the leaves below, only the upper pair with two seeds each and about twice as long as the second pair. Each cone scale apparently with the bract completely fused to the seed-bearing portion and ending in a long, upcurved spine halfway up the scale or a little higher. Seeds oval, with two very unequal wings derived from the seed coat at the upper end, the outer wing a mere fringe, the inner expanding over the scale and overlapping with the wing of its neighbor. Cotyledons two, each with one vein. Chromosome base number x = 11.

Wood fragrant, light, soft, and moderately to extremely resistant to decay, with yellowish to light pinkish brown sapwood sharply contrasting with the dull red or dark yellow to dark brown heartwood. Grain fine to very fine and even, with well-defined or somewhat cryptic growth rings marked by a fairly gradual transition to a narrow band of much smaller and somewhat thicker walled latewood tracheids. Resin canals absent but with sparse to abundant individual resin parenchyma cells scattered through the growth increments or somewhat concentrated in open bands.

Stomates grouped in (often waxy) patches or bands primarily on protected surfaces of leaves, either on the inner face, hidden in grooves, or on the side facing down in horizontal sprays. Each stomate rectangular or a little rounded in outline, sunken beneath and largely hidden by the four to six surrounding subsidiary cells, which are often shared within and between rows and usually circled by a tall, steep, nearly continuous Florin ring. Subsidiary cells and other epidermal cells in stomatal zones also sometimes carrying additional rounded papillae. Midvein single-stranded above a single large resin canal and flanked in part by wedges of transfusion tissue. Photosynthetic tissue forming a palisade layer beneath the epidermis and accompanying thin hypodermis all around the external face or only on the up-facing side of flattened sprays, the remaining leaf volume occupied by looser spongy mesophyll, especially near the stomatal bands and patches.

Five species in Chile, New Caledonia, and New Zealand. Until the 1950s, most botanists included all of the incense cedars in both the northern and southern hemisphere, with their fragrantly resinous wood, in a single genus, Libocedrus (from the Greek “teardrop cedar” for the resinous exudate), the only conifer thought to have such a bihemispheric distribution. Then Li (1953) and Florin and Boutelje (1954) presented convincing arguments for breaking up this genus, and most subsequent authors followed their lead (de Laubenfels 1988 is one exception). DNA data generally support most of the distinctions. The northern hemisphere species, placed in the genus Calocedrus, are really more closely related to other northern genera, like Platycladus, than they are to any of the southern incense cedars, just as Li suggested. While the southern species are all related to one another, there is ample justification for separating the South American Austrocedrus and the New Guinean Papuacedrus. Since the New Zealand Libocedrus plumosa is the type species of the genus, the New Zealand and New Caledonian species retain the name Libocedrus. Some species of Libocedrus are cultivated to a limited extent outside of their native ranges in botanical collections indoors or outdoors in suitable mild, wet places, but no cultivar selection has taken place.

Both Austrocedrus and Papuacedrus have short projections of the bracts on their seed scales, at the top and bottom in the two genera, respectively, while the species of Libocedrus have a much longer prickle near or above the middle. Although the bract and seed scale in Libocedrus and its relatives are here referred to conventionally as fused, this is a theoretical interpretation of the evolutionary origin of these structures. The actual development of the seed cones presents no clear fusion of two separate structures but rather differential growth of the free and united portions of the bract and seed scale.

Ironically, the segregate that superficially appears most distinct and the one first generally accepted as such, Pilgerodendron uviferum is actually firmly nested among the five New Caledonian and New Zealand species in the DNA studies. Although its seed cones are similar to those of the other species, it has square branchlets that lack the wide lateral leaves often considered typical of incense cedars. However, Libocedrus bidwillii of New Zealand has similar adult foliage, and Libocedrus chevalieri of New Caledonia also has weak differentiation of lateral and facial leaf pairs. These three species occur at the ecological extremes of the range of the genus. Pilgerodendron uviferum and Libocedrus bidwillii occur in the coldest climates, and Libocedrus chevalieri in the driest. Expanded lateral leaves, like those of the other three species of Libocedrus (and the related Papuacedrus) are found in areas with a warm, moist climate. Fossils assigned to Libocedrus have been found in Oligocene sediments of Tasmania and later Mio-Pliocene deposits in New Zealand. Since the earlier fossils are contemporaneous with Tasmanian fossils assigned to Austrocedrus and Papuacedrus they also support the separation of these genera.  

Species:

Attribution from: Conifers Garden