Coniferales

 

Araucariaceae

 

This evergreen, decorative family of conifers is found principally in the Southern Hemisphere. It is a relatively early development in the evolution of conifers and, although during the Jurassic was widespread and diverse, is now only represented by three surviving genera – Agathis, Araucaria and the very recently discovered Wollemia in Australia. The trees are generally large timber trees with whorls of branches developing on a single upright bole. The seeds are produced in large cones which only have one seed per scale – in some species these are individually very large and have a food reserve which is predominantly waxy. There are no endogenous or seed coat blocks to dormancy.

 

The genus Agathis consists of sixteen species, all of which are subtropical and tropical in distribution from Fiji through the Philippines to the Malay Peninsula – the most cold tolerant is the Kauri Pine (Agathis australis) from the very north of New Zealand - but it is not hardy enough to survive for long in temperate climates - even in the far south west of the UK.

 

They are tall, evergreen, very resinous trees with massive columnar trunks and whorls of horizontal branches – usually losing shape and grace as they mature and become large and aged. All the species are sought after timber trees.

 

Some of the more cool tolerant species could be grown in warm temperate areas but production would depend on importing seed. Seed is produced abundantly but much of it is not sound – however this cannot be separated readily by flotation as much sound seed also floats - it is therefore necessary to pick over the sample by eye. There are no apparent blocks to germination and seed emergence is rapid and uniform if the medium is maintained at c25ºC and moist. Because of the thin seed coat imbibition is rapid and efficient - and emergence is thus tightly synchronised. The only proviso is not to sow the seeds too deeply as the hypocotyl is weak and is unable to push through any significant depth of compost (c1cm).

 

The genus Araucaria is also chiefly subtropical and tropical in distribution and in the present time is found in Chile and Argentina, Australia and New Zealand, and the adjacent Pacific Islands - despite its virtually global distribution in the Jurassic and Triassic. However one species - A. araucana (the Monkey Puzzle tree or the Chilean Pine) - is cold tolerant and occupies particular niches in the high regions of the Southern Andes in both Chile and Argentina - where it is found as a dominant tree in the high forests and where it is associated with the Southern Beech (Nothofagus obliqua). This region, although having a cold temperate climate, is also subject to wildfire and the tree will sprout from epicormic shoots if killed out above. All the species are tall regular shaped trees and have single, strong, upright trunks and symmetrical crowns. The branches are produced in the characteristic whorls. They are native of climates with more than 1250mm of rainfall per annum and occur on well drained soils.

 

The species are normally monoecious but the cold temperate species can be dioecious. The flowers are produced in the spring and the cones mature after two or even three years. The cones are large, almost spherical to pineapple shaped and can weigh several pounds; they are initially green but as they dry and ripen they become dark tan coloured. The cones disintegrate on the tree to liberate the seeds but sometimes the whole cone falls and smashes on impact. There is little dispersal of the seed by wind – it would appear that they are generally moved by birds or animals.

 

The large three dimensional seeds, shaped rather like a WW II bomb, have rudimentary wings; they are carried one per scale to which it adheres initially. The seeds can be picked up from the ground or the harvested ripe cones can be dried for a short period when they will disintegrate and the seeds can be hand picked. These large seeds have a thin seed coat and an endosperm consisting of lipids; thus ordinary dry storage sees a fairly rapid deterioration in viability levels. Good viability levels however can be maintained if the fresh seed is kept in cold storage at c3ºC under moisture conserving conditions. This will give a longevity of three or four years. The seeds are elongate, to 30 to 35 mm long in some species and contain a large well developed embryo which is almost as long as the seed – it has two cotyledons.

 

None of the species exhibit any dormancy controls and the germination of all species will be rapid (c21 days) and uniform if the seeds are kept moist and subjected to a warm temperature of 20 to 25ºC.

 

The only other crucial feature for the production of good quality seedlings, during the germination process, is to sow these large seeds ‘the right way up’ (ie with the correct polarity). The seeds should be sown point downwards so that the orientation of the radicle and plumule within the embryo provides the correct juxtaposition for the components of the seedling at emergence, this produces an immediately upright seedling which will grow faster (it doesn’t have ‘to waste time’ in tropic growth to correct the polarity). As the seeds are large and produce a substantially sized seedling at germination, the seeds are best sown individually in suitable sized containers.

 

Although all the species of Araucaria are important timber trees in their natural habitats, the following species are useful as ornamental trees in temperate and warm temperate climates – A. heterophylla (the Norfolk Island Pine – which is very wind and salt tolerant), A. bidwillii (the Bunya Bunya from Eastern Australia), A. columnaris (the Cook or New Caledonian Pine) and A. cunninghamii (the Colonial Pine). These species are sometimes offered in the UK as container grown trees for cultivation in conservatories.

 

Wollemia nobilis was only recently discovered in an inaccessible gorge in the Wollemi National Park in New South Wales – it is apparently a very narrow endemic to this area where less than 200 trees of all ages were found. It has been widely propagated and distributed in order to protect it in its native habitat. Eventually seeds will no doubt be distributed commercially and one day mature specimens in cultivation will produce seeds.