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Celery pine, L. Richard et A. Richard  1826

Phyllocladus - Celery pine description


Evergreen trees and shrubs, with multiple trunks or a single, upright, cylindrical to slightly fluted main trunk. Bark obscurely fibrous, thin, smooth and with numerous warty lenticels or scaly and sometimes becoming shallowly and irregularly ridged and furrowed. Crown dense, broadly conical to dome-shaped, initially with regularly spaced whorls of upwardly angled branches. Branchlets dramatically differentiated into long and short shoots. Long shoots forming the trunk and branching framework of the plant, of ordinary twiggy appearance, hairless, grooved between the attached bases of the scale leaves, remaining green for at least the first year. Shoot shoots in the form of phylloclades: flattened, leaflike, and photosynthetic twigs (hence the scientific name, Greek for “leaf stem”). Phylloclades lobed or toothed and, like true foliage leaves, either simple (a single segment attached directly to a long shoot) or compound (with few to many segments attached pinnately to a common axis). Each phylloclade segment flattened side to side, usually with photosynthetic tissue on both faces, stomates only on the underside, and with a more or less well developed midrib, representing the main axis of the branchlet, and bearing many branch veins extending out to minute scale leaves at the periphery. Both simple and compound phylloclades, as well as phylloclade segments, may resume growth and produce new phylloclades or whole long shoots and hence are not, strictly speaking, short shoots, but often grow as if they were. Resting buds as the tip of long shoots, well developed, tightly enclosed by specialized bud scales. Leaves spirally attached on long shoots, in a flattened plane around phylloclades, scalelike and often quickly shed in adults, needlelike and flattened top to bottom in juveniles. Juvenile foliage giving way quickly in the second year or much later to scale leaves and phylloclades of adult foliage.

Plants monoecious or dioecious or sometimes even with a few cones of mixed sex. Pollen cones in spirally arranged clusters of 1-25 on short stalks or directly in the axils of bracts near the end of a short branch. Each pollen cone cylindrical, without a ring of bracts at its base and with numerous (25-75), spirally arranged, roundly triangular pollen scales, each bearing two pollen sacs. Pollen grains small (body 15-35 µm long, 20-40 µm overall), with two small, smooth or wrinkled air bladders tucked underneath around the germination furrow and barely protruding beyond the ends of the minutely bumpy, oval body. Seed cones single or in tight clusters of two to four on short stalks or directly attached in various positions on the phylloclades, in notches at the tips or sides of simple phylloclades or of segments of compound phylloclades, or replacing whole lower phylloclade segments. Each seed cone compact, with 3-40 spirally arranged bracts, of which the middle 1-10(-20) are fertile and bear one ovule apiece. Bracts often uniting and becoming fleshy with maturity, what could be the equivalent of seed scales (or epimatium) developing late in the form of an aril. seeds without wings, egg-shaped, slightly flattened, the opening pointed upward rather than down into the cone axis, surrounded at the base by a thin, leathery or fleshy cuplike aril, maturing in one (or two) season(s). Cotyledons two, each with two veins. Chromosome base number x = 9.

Wood heavy, strong, hard, and fragrant, the white to very light brown sapwood strongly contrasting with the small core of yellowish brown to orange-brown heartwood. Grain fine and even, with well-developed growth rings marked by obvious bands of darker latewood. Resin canals and individual resin parenchyma cells both absent.

Midvein of juvenile leaves single, prominently raised beneath, with one or two resin canals immediately beneath it. Juvenile leaves with photosynthetic tissue along the upper side and lines of stomates in stomatal bands on either side beneath, each stomate surrounded by a sunken Florin ring.

Five species in Malesia, New Zealand, and Tasmania. The common name celery pine refers to the appearance of compound phylloclades, which are somewhat reminiscent of the leaves of celery above the stalk. Despite their distinctive and attractive appearance, species of Phyllocladus are cultivated to a very limited extent outside New Zealand and Australia. The few cultivars selected have blue-green phylloclades because of extra wax. Natural hybridization occurs between some species and may become a source of new cultivars in the future.

The extraordinary phylloclades of the celery pine are unique among the conifers making this group one of the most distinctive conifer genera. To this can be added other features unusual among the Podocarpaceae, including the aril of the seeds and the reduced air bladders of the pollen grains with a corresponding shift in mode of pollination. Small wonder, then, that many authors separate Phyllocladus into its own family, called Phyllocladaceae, while still acknowledging its closeness to Podocarpaceae. A few workers went even further and essentially denied any more particular connection of Phyllocladus to the Podocarpaceae than it has to some other groups. For instance, Keng (1974), emphasizing the phylloclade, suggested that Phyllocladus represents a direct link to the Paleozoic progymnosperms, a seedless group generally viewed as containing the ancestors of all seed plants. Similarly, Melikian and Bobrov (2000), emphasizing the aril and other seed features, placed Phyllocladus close to the yews (Taxaceae). When all features are taken together, however, including wood anatomy, chemistry of the wood and foliage, structure of the pollen and seed cones, embryo development, cotyledon structure, and organization of the chromosomes, the inclusion of Phyllocladus within the family Podocarpaceae seems inescapable. DNA studies generally confirm this assessment but suggest conflicting placements within the family. Depending on the genes examined, it has been seen either as sister group to all of the remaining genera or as a member of one of the two main groups of genera within the family, the one containing Prumnopitys and the scale-leaved genera like Halocarpus and Parasitaxus. In either case, it would not be closely related to the other genera with condensed, multiscaled cones, Microcachrys and Saxegothaea, which belong to the other grouping in the family, the one containing Podocarpus itself.

The pollination mechanism in Phyllocladus, with pollen captured directly in a small, upright pollination droplet, is different from that in the vast majority of Podocarpaceae, which produce a large, hanging drop in which pollen grains that have landed on the dry seed cone are later swept up and float into the opening (micropyle) of the ovule. The method of pollen capture in Phyllocladus is more similar to that found in many unrelated conifers in the families Cupressaceae and Taxaceae but is also not all that dissimilar from the one found in Acmopyle, another genus whose ancestors may have had a fairly early divergence within the Podocarpaceae. After successful pollination and fertilization, embryo development follows a pattern found in all other genera of and known only from Podocarpaceae in which one group of cells (the E tier) within the proembryo all have two nuclei rather than the single one found in other conifers. Thus the preponderance of evidence favors inclusion of celery pines within Podocarpaceae but in a relatively basal position.

The distinctive phylloclades of the genus are found as fossils in sediments dating back to the late Eocene (about 40 million years ago) in southeastern Australia, both in Tasmania, where the genus persists to this day, and on the mainland, where it became extinct, presumably due to increasing aridity since all of the living species live in wet climates. The earliest records from New Zealand, where three of the five extant species grow, only date from the Miocene, about 20 million years ago, based on both phylloclades and wood. Pollen grains apparently referable to Phyllocladus are more widespread and extend further back in time. Even the records from the Jurassic, 150 million years ago, could really belong to Phyllocladus and not to some extinct genus if the celery pines are the sister group to all other extant Podocarpaceae, as some DNA studies suggest.




Attribution from: Conifers Garden