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Pink pine, C.J. Quinn 1982

Halocarpus - Pink pine description


Evergreen trees and shrubs. Trunk(s) single or multiple, short or extended, straight, bowed, or crooked, cylindrical or asymmetrical. Bark obscurely fibrous, smooth or with horizontal ridges at first, later shedding in irregular flakes and scales. Crown dome-shaped or almost flat-topped, often extending to the ground and spreading much wider than high, dense is youth, remaining so or opening up with age, with heavy, horizontal to upwardly angled branches. Branchlets all elongate, without distinction into short and long shoots, hairless, remaining green for at least the first year, shallowly grooved between the attached leaf bases in juvenile foliage, completely hidden by the scale leaves in adult foliage. Resting buds not differentiated, consisting solely of the new, as yet unexpanded ordinary foliage leaves. Leaves spirally attached. Juvenile foliage sharply distinct from and giving way abruptly without extended transitional forms to adult foliage. Commonly with equally abrupt reverse transitions and both foliage types usually found on mature trees. Juvenile leaves needlelike, types usually found on mature trees. Juvenile leaves needlelike, sword-shaped, flattened top to bottom, standing out sharply from the twigs and usually gently curved downward along their length. Adult leaves scalelike, tightly pressed against the twigs and overlapping, the ex-scalelike, tightly pressed against the twigs and overlapping, the exposed portions more or less diamond-shaped, keeled or rounded, with a thin, papery fringe at the tip.

Plants dioecious. Pollen cones one (or three) at the tips of otherwise ordinary foliage shoots. Each pollen cone cylindrical, with a few bracts at the base and with 10-20 spirally arranged, roundly triangular pollen scales, each bearing two pollen sacs. Pollen grains small to medium (body 20-45 µm long, 35-75 µm overall), with two round, internally strongly striated air bladders. Bladders partially tucked underneath the conspicuously larger, minutely bumpy, oval body around the germination furrow, but also extending well beyond its ends. Seed cones single at the tips of otherwise ordinary foliage shoots, highly modified and reduced, maturing in one or two seasons. Cone with about 5-15 closely spaced, spirally arranged bracts, which may become slightly fleshy but do not unite into a podocarpium. Middle (one or) two to five bracts fertile, from which one to three (to five) seeds mature. Each fertile bract bearing a single seed that has its opening pointed back down into the cone axis and is completely covered by not united with the seed scale (the epimatium). Seed and epimatium hard, flattened, ribbed, and with a thick crest extending around the sides and over the top, nestled at the base in a thick, fleshy, cuplike aril (hence the scientific name, Greek for ‘halo fruit’). Cotyledons two, each with two veins. Chromosome base number x = 9, 11, or 12.

Wood fragrant, dense and hard, strong or brittle, and durable, the creamy white sapwood sharply or gradually contrasting with the light brown to pinkish brown heartwood. Grain very fine and even, with clear growth rings marked by variable widths of darker latewood. Resin canals and individual resin cells both absent.

Stomates in irregular patches on both sides that are not arranged in lines or in any one direction. Each stomate sunken beneath and largely hidden by the four to six inner subsidiary cells, which may be surrounded by a less organized circle of another four to six, and topped by a sunken, interrupted Florin ring. Cuticle in some species thicker than the epidermal cells that support it. Midvein single, inconspicuously buried in the leaf tissue of the adult leaves, with one resin canal immediately beneath it. Photosynthetic tissue on both sides of the leaf, not surrounded by hypodermis inside the epidermis.

Three species in New Zealand. The species in this small, geographically restricted genus of small trees and shrubs are all morphologically very similar to one another. Each species, however, has a genetic complement with a different number of chromosome pairs. These differences are actually underlain by a basic similarity since each complement is based on sixteen chromosome arms that are grouped together differently to make chromosomes in the three species. Similar differences in chromosome number in most other podocarp species are based on a complement of 20 chromosome arms. Nonetheless, DNA studies show that Halocarpus is reasonably closely related to Lagarostrobos of Tasmania, Manoao of New Zealand, and Parasitaxus of New Caledonia, all of which have the 20 chromosome arms standard in the family.

The loss of chromosome arms compared to the standard 20 found throughout most of the family might be a point in favor of a result found in only some DNA studies that suggests that Halocarpus is especially closely related to the bizarre celery pines (Phyllocladus), which have an intermediate number of arms (18). Both of these genera also have the mature seeds seated in an aril, an uncommon structure in the family, but their arils might not be directly comparable structures. While both develop late in the maturation of the seeds, the aril of Halocarpus is an outgrowth of the epimatium while that of Phyllocladus arises from the base of the seed itself. Whether there is an underlying common evolutionary origin for the arils of these two genera is worthy of further investigation and might shed some light on whether they are mutually closest relatives within the family as well. If so, features in Halocarpus might help in interpreting the highly unusual morphology of Phyllocladus. The species of Halocarpus are not in general cultivation, and no cultivar selection has taken place. There is no known fossil record of Halocarpus that could contribute to understanding these problems or reveal whether the genus was once more widely distributed.




Attribution from: Conifers Garden