Araucariaceae  

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Araucariaceae is a very ancient family of conifers. It achieved its maximum diversity in the Jurassic and Cretaceous periods, when it was distributed almost worldwide. At the end of the Cretaceous, when dinosaurs became extinct, so too did the Araucariaceae in the northern hemisphere.

Today 41 species are known, in three genera: Agathis, Araucaria and Wollemia. All are derived from the Antarctic flora^{[citation needed]} and distributed largely in the southern hemisphere. By far the greatest diversity is in New Caledonia (18 species), with others in Australia, Argentina, New Zealand, Chile, Southern Part of Brazil and Malesia. In Malesia Agathis extends a short distance into the northern hemisphere, reaching 18°N in the Philippines. All are evergreen trees, typically with a single stout trunk and very regular whorls of branches, giving them a formal appearance. Several are very popular ornamental trees in gardens in subtropical regions, and some are also very important timber trees, producing wood of high quality. Several have edible seeds similar to pine nuts, and others produce valuable resin and amber. In the forests where they occur, they are usually dominant trees, often the largest species in the forest; the largest is Araucaria hunsteinii, reported to 89 m tall in New Guinea, with several other species reaching 50–65 m tall. A. heterophylla, the Norfolk Island Pine, is a well-known landscaping and house plant from this taxon.

Fossils widely believed to belong to Araucariaceae include the genera Araucarioxylon (wood), Brachyphyllum (leaves), and Protodammara (cones). In Arizona, the petrified woods of the famous petrified forest in Petrified Forest National Park belong to several species of Araucarioxylon, the most common of them being Araucarioxylon arizonicum. During the Upper (Late) Triassic, the region was moist and mild. The trees washed from where they grew in seasonal flooding and accumulated on sandy delta mudflats, where they were buried by silt and periodically by layers of volcanic ash which mineralized the wood. Some of the segments of trunk represent giant trees that are estimated to have been over 50 meters tall when they were alive.

Further reading

• Cookson, I. C. and Duigan, S. L. (1951) "Tertiary Araucariaceae from South-eastern Australia, with notes on living species" Australian Journal of Scientific Research Series B (Biological Sciences) 4: pp. 415–449
• Kendall, Mabel W. (1949) "A Jurassic member of the Araucariaceae" Annals of Botany, New Series 13(50): pp. 151–161
• Kershaw, Peter and Wagstaff, Barbara (2001) "The Southern Conifer Family Araucariaceae: History, Status, and Value for Paleoenvironmental Reconstruction" Annual Review of Ecology and Systematics 32: pp. 397–414, doi: 10.1146/annurev.ecolsys.32.081501.114059
• Krasilov, Valentin A. (1978) "Araucariaceae as indicators of climate and paleolatitudes" Review of Palaeobotany and Palynology 26: pp. 113–124
• Pye, Matthew G.; Henwood, Murray J. and Gadek, Paul A. (2009) "Differential levels of genetic diversity and divergence among populations of an ancient Australian rainforest conifer, Araucaria cunninghamii" Plant Systematics and Evolution 277(3/4): pp. 173–185, doi: 10.1007/s00606-008-0120-1
• Setoguchi, Hiroaki et al. (1998) "Phylogenetic relationships within Araucariaceae based on rbcL gene sequences" American Journal of Botany 85(11): pp. 1507–1516
• Stockey, Ruth A. (1982) "The Araucariaceae: an evolutionary perspective" Review of Palaeobotany and Palynology 37: pp. 133–154
• Stockey, Ruth A. (1994) "Mesozoic Araucariaceae: morphology and systematic relationships" Journal of Plant Research 107(4): pp. 493–502, doi: 10.1007/BF02344070