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Dacrycarp, (Endlicher) de Laubenfels  1969


Evergreen trees and shrubs, sometimes of giant stature. Usually with a single straight trunk that may be cylindrical, with little taper, or fluted and buttressed. Bole free from branches for half or more of its height but, in shrubby individuals of exposed places, dividing near the ground into a few divergent limbs. Bark basically smooth but often with abundant small warts on young trees, remaining thin and breaking up into checkers or shedding irregular flakes and scales with age. Crown conical at first, becoming cylindrical with maturity and finally open, spreading and flat-topped or shallowly dome-shaped. Crown framework with a few major limbs and more numerous slender, rising branches. Lesser limbs breaking up into many branchlets densely clothed with compact foliage. Branchlets green for at least the first year, grooved between the attached leaf bases, of two types. Short shoots limited to a single increment of growth and bearing elongate foliage leaves, confined mostly to juveniles, where they make up a large percentage of the annual growth, but also borne sporadically and in varying proportions on adult trees. Long shoots with continuing growth bearing photosynthetic scale leaves and making up the bulk of adult foliage. Resting buds relatively inconspicuous and unspecialized, consisting of undeveloped foliage leaves. Leaves spirally arranged, closely and evenly spaced along and radiating all around the twigs, of two main types. Elongate leaves of short shoots flattened into two rows by twisting of the twigs between successive leaves and flexure of the lower portion of the leaf. These leaves flattened side to side rather than top to bottom, slightly sickle-shaped. Midrib raised and flanked by lines of stomates on both sides. Scale leaves of long shoots maintaining their radiating orientation, flattened top to bottom, triangular to sword-shaped, and variably curled forward with their tips rather spreading to tightly pressed to the twigs.

Plants dioecious. Pollen cones spherical to cylindrical, single at the tips of short, scaly, axillary stalks or of short shoots. Base of cone with a few bracts transitional between the scale leaves of the stalk and the numerous, spirally arranged pollen scales, each bearing two pollen sacs. Pollen grains medium to large (body 30-60 µm long, 50-85 µm overall), with three rounded air bladders evenly speced around the body and nearly touching at their points of attachment. Each bladder about the same size as to substantially smaller than the body, with coarse, squiggly sculpturing on the bladders and minutely bumpy over the body. Cap thicker and more coarsely dotted than the germination face, sometimes with a three-pointed scar where the grain was in contact with its three sibling grains during development. Seed cones held upright at maturity, single at the tip of short leafy stalks in the axils of foliage leaves or at the ends of short shoots, maturing and falling in a single season. Cones highly modified and reduced, with a circle of variably developed, radiating free bracts at the base. Reproductive part with two to five bracts, these joining with the cone axis and each other, swelling, and becoming red to purple or black and juicy at maturity to form a warty podocarpium with leafy free bract tips. Upper one to three (or four) bracts fertile but only one usually maturing a single, plump, unwinged seed. Seed embedded in the leathery black or brown seed scale (the epimatium), covered with a thin, waxy film, the opening pointing down into the cone axis. Abortive seeds often enlarging considerably before their arrest and persisting as conical, black protuberances at the tip of the mature seed cone. Seeds roughly spherical, with a single or paired, generally low crest over the top formed by fusion of the fertile bract associated with the seed scale. Cotyledons two, each with two veins. Chromosome base number x = 11.

Wood hard, dense, on the heavy side for a softwood, not fragrant, the wide, white to creamy white sapwood slowly developing into pale to bright yellow od light brown heartwood. Grain fine and even, with growth increments delimited by narrow bands of inconspicuously darker latewood. Resin canals absent.

Stomates of scale leaves in patches confined to or more abundant on the upper side. Each stomate sunken beneath and partially hidden by the four to six subsidiary cells, which are sometimes shared between adjoining stomates in a line or flanked by a partial outer row of extra cells, or topped by a well-defined Florin ring. Midrib raised beneath and flat above, with one resin canal underneath and little development of sclerenchyma. Cross section of needle leaves with one resin canal beneath the midvein (but seeming to be on the trailing or outside edge of the leaf) and a wedge of sclerenchyma above (but seeming to be on the leading or inside edge of the leaf). Photosynthetic tissue with a thin palisade layer lining both the right and left faces.

Nine species in the southwestern Pacific region from northern Myanmar and southernmost China south through Indo-China and all of Malesia to New Caledonia and Fiji, and in New Zealand.

Two species in the genus, common dacrycarp (Dacrycarpus imbricatus) and kahikatea (Dacrycarpus dacrydioides), are among the largest trees in the family Podocarpaceae, forest giants rivaled only by broadleaf miro (Prumnopitys amara) and rimu (Dacrydium cupressinum), which also grow in the same region. They are also common enough to be important timber trees. The species are all so similar in appearance and overlapping in habitat and habit (most can be either shrubs or trees depending upon ecological conditions) that they are typically not distinguished by local people when two or more are found in the same region. For instance, in New Guinea, with five species of dacrycarps, the greatest concentration of any region, the name pau has been recorded for four of the species among Enga speakers, while umba is used for at least three by Chimbu speakers. Species of Dacrycarpus have basically not entered into horticulture beyond the limits of a few botanical gardens, and there has been no cultivar selection.

The species of Dacrycarpus were long included as one of the more distinctive sections within Podocarpus. As the same time, many authors recognized similarities of these species to other genera with respect to some features that are not found in true Podocarpus species. Pollen grains normally with three air bladders, for instance, are elsewhere found only in Microcachrys and Microstrobos among extant Podocarpaceae. The warty podocarpium with several fertile bracts and the juvenile leaves flattened side to side are both features found also in Acmopyle. The adult foliage, on the other hand, is reminiscent of species included in Dacrydium. This similarity is reflected in the name of the genus (Greek for “teardrop fruit”), proposed as a sectional name in Podocarpus 40 years after the publication of the generic name Dacrydium. In fact, DNA studies show that Dacrycarpus is closely related to Dacrydium and Falcatifolium and only more distantly to Acmopyle, Microstrobos, and Microcachrys, and to Podocarpus, from which it was segregated in 1969. Dacrycarpus differs from all other genera of the Podocarpaceae in the fusion of the fertile bract with the seed scale to form a crest along the side of the epimatium that ends in a sideways beak.

Although kahikatea and the New Caledonian Dacrycarpus vieillardii were each segregated into a genus separate from the other Dacrycarpus species (and Dacrycarpus dacrydioides was even placed in a separate family) in the extremely subdivided revision of the Podocarpaceae and Taxaceae by morphologists Melikian and Bobrov (2000), their proposals are unlikely to be widely accepted. Their proposed classification is based almost entirely on narrowly defined details of the structure of the seed coats and contradicts an enormous amount of traditional morphological evidence as well as all published DNA studies based on analysis of several portions of both the chloroplast and nuclear genomes. Hence their names are all treated as synonyms here. Nonetheless, the sampling of species used in DNA studies will need to be greatly increased before relationships among the genera and species of Podocarpaceae are fully resolved.

While Dacrycarpus species are overwhelmingly tropical today, with kahikatea of New Zealand as the only species in a (very mild) temperate region, the fossil record of the genus as found almost exclusively in presently temperate regions. The fossil record of its foliage is one of the richest among the podocarps of the southwestern Pacific region. The oldest confirmed fossils are found in Eocene sediments 40 million years old or more in southern South America and in southeastern Australia (including Tasmania), both regions where the genus is extinct today. Somewhat older fossils assigned to extinct genera may also be related to Dacrycarpus but do not match any living species in the structure of their epidermis, which provides most of the characters used for assigning fossil foliage to this genus. The record in Australia is particularly rich, and the progressive reduction in leaf size and in the amount of the leaf surface occupied by stomates after the early Eocene has been interpreted as reflecting the increasing aridity of that continent. The genus seemingly became extinct in mainland Australia during the Miocene, about 20 million years ago, but it persisted in Tasmania much later and may not have succumbed until the Pleistocene ice ages of the last 2 million years, although there is some doubt about the identification of these late fossils. Dacrycarpus  seems to be a relative latecomer to New Zealand, where the earliest  confined foliage specimens date from the Miocene, and the fossil record there is surprisingly sparse considering the historical abundance of kahikatea in swampy ground on both islands.





Attribution from: Conifers Garden