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Arartree, M.T. Masters  1892

Tetraclinis - Arartree description


Evergreen shrubby trees with one to several frequently much branched and crooked trunks clothed with thin, fibrous bark gradually roughening into broken ridges. Branchlets strongly flattened, vertically oriented, brittle at the joints between successive leaves, arranged in flattened sprays because virtually all branching (which is mostly alternate) arises in the axils of lateral leaves. Within the transient juvenile phase needlelike; those of adults scalelike, with long attached bases clothing the twig and very short free tips sometimes fringed with tiny hairs. Adult leaves differentiated into facial and lateral pairs, the lateral pairs completely separated by the facial pairs and parallel to them, thus seemingly in whorls of four, like those of Calocedrus, with small glands at the tip.

Plants monoecious. Pollen cones single at the ends of short branchlets on a short, slender stalk emerging from a few alternating pairs of bracts that are transitional to the foliage leaves of the supporting branchlets. Individual cones oblong, with five or six alternating pairs of pollen scales. Each scale shield-shaped, the face triangular to pentagonal, with a slender central stalk and four or five pollen sacs. Pollen grains small (25-35 µm in diameter), nearly spherical, almost featureless. Seed cones single at the ends of short branchlets, maturing and gaping open in a single season. Individual cones almost spherical, with two nearly equal alternating pairs of woody seed scales attached at their bases around a common base. Each cone scale composed of an intimately united seed-bearing scale and bract, with a distinct triangular point (of the bract) below the tip, the smaller (upper) pair meeting at their tips, sterile (or with a single abortive seed) and strongly grooved, the larger, more convex pair not touching each other, with (one or) two (or three) seeds. Two additional seeds sitting at the center of the cone and possibly representing an otherwise lost third the related (Calocedrus). Seeds oval with two roughly equal wings forming an obtuse angle with and running along the seed body and beyond, and much wider than it, the wings derived from the seed coat. Cotyledons four, each with one vein. Chromosome base number x = 11.

Wood very fragrant, relatively heavy and hard, the whitish to yellowish sapwood sharply contrasting with the reddish brown to dark chocolate brown or almost black heartwood. Grain very fine and somewhat wavy, with weakly developed growth rings marked by an abrupt transition to one to three rows of smaller but not notably thicker-walled latewood tracheids. Resin canals absent but with a scattering of individual resin parenchyma cells.

Stomates confined to very limited stomatal zones near the tips of the leaves on their inner face and especially lining the grooves between the bases of adjoining lateral and facial leaves. Each stomate sunken beneath and largely hidden by the four to six surrounding subsidiary cells, which are topped by a steep,  lobed Florin ring, the remaining epidermal cells in the grooves also often topped by rounded or irregular papillae. Midvein weak, close to the inner edge of the attached leaf base, petering out quickly in the free tip, with little or no accompanying transfusion tissue. Photosynthetic tissue with a single palisade layer inside the epidermis and thin hypodermal layer lining all exposed leaf surfaces, including the attached bases, but displaced from the area of the leaf tips where the centrally located, spherical to oblong resin gland lies directly beneath the epidermis. Spongy mesophyll filling the remainder of the leaf and merging with the stem tissue of the facial leaves.

One species in the western Mediterranean. Tetraclinis was historically considered the sole northern hemisphere member of the southern hemisphere group of Cupressaceae, with special similarity to Widdringtonia. Although the cones superficially resemble those of Widdringtonia, details of their structure and development do not. The foliage is more like the northern Calocedrus, and leaf pigments and DNA studies also demonstrate a relationship to northern genera, particularly Calocedrus, Microbiota, and Platycladus. Tetraclinis articulata, while of moderate economic importance, in not terribly ornamental and is scarcely in cultivation outside of its native range and botanical gardens so no cultivar selection has taken place.

The oldest known fossil remains of Tetraclinis are from early Eocene (or latest Paleocene) sediments in Europe more than 50 million years old. By the Oligocene, more than 30 million years ago, similar trees were also growing in North America. While they died out in North America during the Miocene, there is a more or less continuous record in Europe into the early Pliocene, some 3 million years ago. There are no records for either Asia or the southern hemisphere, providing further evidence for the northern affinities of the genus.




Attribution from: Conifers Garden