Wollemi pine, W.G. Jones, K.D. Hill & J.M. Allen 1995
Araucariaceae

Wollemia - Wollemi pine description

Evergreen trees with one to many (by natural coppicing) straight, slender trunks clothed with unique bark made up entirely of densely packed bumps. Original branches in distinct tiers, upright at first, then flattening and arching with age until a pollen or seed cone is initiated at their tip after several years of growth increments and they fall after cone maturation and are replaced by new ones growing out from the trunk in irregular positions. Resting buds loosely wrapped by short needle leaves but without specialized bud scales. Leaves opposite or nearly so, needlelike, broadly sword-shaped, flat, without a midrib and with numerous parallel veins, their bases running down onto the stem without an intervening petiole, remaining on the branch until it falls. Juvenile leaves in two horizontal rows, proportionately longer, narrower, and more sharply pointed than the adult leaves. Adult leaves in four rows, with two horizontal rows and two rows forming a V-shaped trough above these, each leaf pair contributing one leaf to a horizontal row and another to the opposite row of the trough.

Plants monoecious. Pollen cones solitary and hanging at the end of branches in the lower portion of the crown. Individual pollen cones not stalked, large, cylindrical, with hundreds of pollen scales, and cupped in a ring of about eight small bracts. Each scale shieldlike, with a large angular boss projecting from the surface and with four to nine elongate pollen sacs. Pollen grains small to medium (30-60 µm in diameter), spherical, minutely bumpy with interspersed larger and smaller granules but otherwise nearly featureless. Seed cones solitary and horizontal to partially upright at the end of branches in the upper portion of the crown after 3-6 years of growth, maturing in 2-3 years and shattering at maturity leaving the bare cone axis and a few basal scales behind. Individual seed cones spherical in outline but the shape obscured by the long, bladelike tips of the hundreds of spirally arranged cone scales, which almost double the apparent cone diameter. Each cone scale with complete fusion of the bract and seed scale portions, broadly winged on either side to yield a rhombic outline overall, contracting abruptly to the free tip that emerges from the broadly and narrowly diamond-shaped external face. Seeds solitary at the midline of the scales, inverted (attached near the far tip and with the original pollination opening pointed toward the cone axis), detaching separately and more or less evenly narrow-winged around the margin. Cotyledons two, each with six to eight veins. Chromosome base number x = 13.

Wood odorless, somewhat glossy, soft and medium in weight, with brownish white sapwood not sharply delimited from the light brown heartwood. Grain very fine and even, with clearly defined growth rings marked by a gradual transition to a narrow band of much smaller but not much thicker walled latewood tracheids. Resin canals and individual resin parenchyma cells both absent.

Stomates not in definable bands, in numerous discontinuous lines beneath and absent (juvenile leaves) or in fewer lines (adult leaves) above. Each stomate sunken beneath and partly hidden by the four to six surrounding subsidiary cells, which are themselves sunken beneath the level of the other epidermal cells (and are thus neither shared between neighboring stomates nor topped by a Florin ring). Leaf veins midway between the top and bottom, parallel, more or less evenly spaced across the width, numbering (5-)8-15 in the widest portion, overlying a cap of transfusion tissue, alternating with large resin canals midway between each pair of veins. Photosynthetic tissue with a well-developed palisade of two or three cell layers beneath the epidermis and well-developed associated patches of hypodermal cells above and a less complete one below, the space in between occupied by spongy mesophyll containing scattered small resin canals and special compartmented cells packed with dark material.

One species in southeastern Australia. Since the two known stands of the sole living species, Wollemia nobilis, in Wollemi National Park (hence the scientific and common names) are about as close to being a single clone as one can get, and are highly homozygous to boot, they have the least natural genetic variation known among the conifers. As a result, we cannot expect much cultivar development once the tree comes into general cultivation, even when it is propagated worldwide, and not just by the massive effort to save the tree undertaken by the Royal Botanic Garden, Sydney. It is now widely available in the form of clonal plantlets produced by tissue culture.

Each pair of living genera in the Araucariaceae shares traits that are absent in the third genus. Wollemia shares more such traits with Araucaria than it does with Agathis, even though two of those shared with the kauris (Agathis), opposite leaves (but in a very different arrangement in each genus) and winged seeds attached atop the cone scale rather than embedded within it, are more conspicuous than most similarities with Araucaria. Because of the phylogenetic structure revealed by DNA studies, traits shared with Araucaria, such as the bristle-tipped cone scales or the special, substance-storing compartmented cells, may be traits inherited from the common ancestor of all three genera. At least, this is a hypothesis that can be explored using a variety of techniques, including genetic, developmental, and paleobotanical studies.

Announcement of the discovery of the sole extant species, Wollemia nobilis, in 1995 created an overnight international sensation exceeding, but nowhere near as long lasting, as the one surrounding the announcement of the discovery of Metasequoia glyptostroboides in 1948, in part because of different world circumstances, closer proximity to large urban centers (if not easier access), and vastly improved communications. The two genera (one species each) were actually quite similar in scientific importance, both having long, geographically extensive fossil records that required reevaluation, and comparable taxonomic and evolutionary implications within their respective families. DNA studies placing Agathis and Araucaria together before they join with Wollemia suggest that many older araucarian fossils previously identified as Araucaria and dating back to the Triassic, more than 200 million years ago, may actually belong to groups ancestral to all three modern genera.

The known fossil record of Wollemia itself (or a close relative) extends back to the mid-Cretaceous, some 95-125 million years ago in the Barremian to Cenomanian stages, making it one of the oldest living conifer genera. Juvenile and adult foliage, pollen and seed cones, and seeds are all present in eastern Australian deposits. Related seed cones are also known from the late Cretaceous of New Zealand. Fossil pollen (reasonably securely) presumed to have been produced by ancient Wollemia trees (and called Dilwynites when dispersed in sediments) was also in Antarctica during the Paleocene, some 60 million years ago. It reached peak abundance during the Paleocene to mid-Eocene (some 60-40 million years ago) in the eastern half of Australia, declined in range and abundance thereafter, and is last recorded as a fossil in Tasmania as recently as 2 million years ago.

References

• Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
• Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
• IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.