In the wild Wollemi Pine trees grow to about 40 metres and their trunks can grow up to 1 metre in diameter.
Like other conifers, it bears cones (male and female), which appear at the very tip of branches with adult phase leaves.
The bark is particularly unusual, looking very much like ‘chocolate crackles’ or bubbling chocolate, making it quite different from the bark of other related species.
The Wollemi Pine has two types (or phases) of leaves. It does not have needles like pine trees in the northern hemisphere. Its young broad-based juvenile leaves are bright lime-green and grow in low light under the rainforest canopy. The adult leaves, which grow in much harsher conditions above the canopy, are tougher and a deeper bluish-green.
The leaves at the beginning and end of a growing season are shorter than those formed during the middle of the season, creating a repeating diamond shaped pattern along the branch. The leaves also have an in-built system to help reduce water loss.
How do the leaves of the Wollemi Pine reduce water loss?
Its leaves have a thick cuticle (a very thin film covering the outer, or epidermis, layer of the leaf), a fibrous hypodermis (a layer of cells just under the epidermis) and sunken stomata (pores), a survival characteristic which helps it reduce water loss.
Further reading: Leaf Anatomy of Wollemi Pine (Wollemia nobilis, Araucariaceae), by Geoffrey Burrows and Suzanne Bullock, Australian Journal of Botany, 47(5): 795-806 (1999).
What is unusual about the bud formation of Wollemi Pine?
Most flowering plants, though not conifers, have dormant buds in the axils (the angles between the upper side of each leaf and the stem) - so if a plant is damaged by insects or pruning, these buds can sprout. In the genus Araucaria and in the Wollemi Pine, each axil has a small group of cells that’s somewhere between a fully formed bud and no bud at all. A unique feature of the Wollemi Pine is that these buds on upright branches develop normally to form a multi-stemmed and multi-branched tree.
Further reading: The Wollemi Pine (Wollemia nobilis, Araucariaceae) possesses the same unusual leaf axil anatomy as the other investigated members of the family, by Geoffrey E. Burrows, Australian Journal of Botany, 47(1): 61-68 (1999).
The Wollemi Pine has two kinds of growth, vertical and horizontal, how does that work?
There are two types of branches on the Wollemi Pine:
1 - one grows upright (orthotropic), forming a stem or another trunk, depending on where it starts.
2 - the other grows sideways (plagotropic) from an upright branch and the leaves develop on these branches. Unlike trees in the genus Araucaria, the sideways branches do not divide unless the growing tip (apical meristem) is damaged.
Upright branches start from buds borne along the trunk, eventually maturing with foliage and a branching structure resembling the initial trunk, so that older trees develop a branched crown. Upright branches that develop from buds at the base of the trunk, referred to as coppicing, form a multi-trunked tree.
Young seedlings, from as early as one year old, can develop more than one upright branch - unlike Araucaria trees where additional upright branches develop only after the growing tip has been damaged or wounded.
Is it normal for a Wollemi Pine to have more than one trunk?
Some dormant buds may sprout along the trunk or from the base of the trunk. This is called coppicing, resulting in large old plants with multiple trunks of different ages - see age and ancestry. This may be a defence against damage from drought, fire or rock fall in the steep canyons where they grow. It‘s probably the reason that the Wollemi Pine has survived the increasing aridity of Australia over millions of years.
Further reading: Architecture of the Wollemi Pine (Wollemia nobilis, Araucariaceae), a unique combination of model and reiteration, by K D Hill, Australian Journal of Botany, 45(5): 817-826 (1997).
Why does the Wollemi Pine shed branches?
The leaves don’t have stalks (petioles) to attach to the branch. Instead, the whole base of the leaf wraps halfway round the branch. So the tree sheds entire lateral branches rather than individual leaves, which is another unusual feature it shares with the genus Araucaria.
Using samples from a trunk collected by the NSW National Parks and Wildlife Service rangers we have been able to examine the anatomy of the wood. See our Image Gallery for these spectacular images taken using a Scanning Electron Microscope.
Further reading : Wood anatomy of Wollemi pine (Wollemia nobilis, Araucariaceae), by R D Heady, J G Banks & P D Evans, IAWA Journal 23(5): 339-357 (2002).