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The 'Araucariaceae' are a very ancient family of conifers. They achieved maximum diversity in the Jurassic and Cretaceous periods, when they existed almost worldwide. At the end of the Cretaceous, when dinosaurs became extinct, so too did the Araucariaceae in the northern hemisphere.
There are three genera with 41 species alive today, ''Agathis'', ''Araucaria'' and ''Wollemia'', all derived from the Antarctic flora and distributed largely in the southern hemisphere. By far the greatest diversity is in New Caledonia (18 species), with others in southern South America, New Zealand, Australia and Malesia, where ''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.
The petrified wood of the famous Petrified Forest east of Holbrook, Arizona are fossil Araucariaceae. 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. The fossil trees belong generally to three species of Araucariaceae, the most common of them being ''Araucarioxylon arizonicum''. Some of the segments of trunk represent giant trees that are estimated to have been over 50 meters tall when they were alive.