We are awed by tall trees, such as redwoods and sequoias. As with elephants or whales, their very size leaves us feeling puny. Their antiquity is also awesome.
Araucarias, trees from the Southern hemisphere, are also in that category. Araucaria araucana, the Monkey Puzzle Tree to the English in the 1850s, can live for 1,800 years and grow to more than 60 m-tall.
These conifers are indeed 30-60 m tall, a feat that raises the question of the ascent of sap to their tip — a point not yet fully understood. This is not their only interesting feature, though.
Another is their leaves, broad and multiveined, which allows for ample water supply to the flat part of the leaf. This feature differentiates them from most conifers whose univeined leaves limit the maximum of leaf width.
The French writer Edmond Baudoin recently (2004) wrote about the araucaria he saw in Chile : ‟It is a tree with hands at its extremities. Offering hands. It is one of the oldest trees on the planet.‟
The overall shape or architecture of these trees conforms to either the Rauh or Massart model. In the Rauh model, an apex may produce either a lateral branch or a lateral inflorescence at any developmental step.
Temperate examples of Rauh’s model include ash, oak, pine, maple trees. In the Massart model, the growth of the trunk is monopodial, rhythmic, and indeterminate. An example is the Norfolk Island pine (Araucaria heterophylla), whose shape is familiar.
Female cones, not quite globe-shaped to ovoid-shaped, are usually borne erect. They take two years to mature. Upon maturity, they fall. Each scale bears a single seed. Seeds from Chilian Araucaria araucana are edible and they are sold in markets. Cones from Australian Araucaria bidwilli can weigh up to 10 kg. Their seeds are likewise edible. Male cones are relatively large, cylindrical, with numerous sporophylls and with about 12 inverted pollen sacs. The pollen grains are wingless.
Today, the genus Araucaria includes only 19 species, 13 of which are endemic to New Caledonia.
The genus originated in the Triassic era, 251.9-247.2 mya. It both expanded and diversified in both hemispheres during the Jurassic (201.3-145 mya) and early Cretaceous (146-100 mya).
They then survived on the Gondwana continent until the Cenozoic (65 mya to the present). Gondwana was the southern portion of the super-continent Pangaea. It stretched from the Equator to the South Pole. In the early Cambrian, between 500 and 600 mya, Gondwana rapidly rotated 60 degrees, which accelerated climate change in all of its regions.
After separating from Pangaea, in the early Mesozoic, 200 mya, Gondwana broke into five fragments which would form the continents of Africa, South America, Antarctica and Australia, and the subcontinent of India, as well as clusters of associated islands of which the biggest are Madagascar, New Guinea and New Zealand.
Those were trees almost entirely restricted to rainforests. Accordingly, their pollen record maps the extent of rainforests in past times. This is documented for southern Brazil, northeastern Australia and New Caledonia, all at a similar latitude. The expansion of Araucaria forest is seen twice in this record, from ca. 190,000-130,000 years ago and from 80,000-45,000 years ago. Now, these magnificent trees face extinction.