Araucariaceae – also known as araucarians – is a very ancient family of coniferous trees. The family achieved its maximum diversity during the Jurassic and Cretaceous periods, when it was distributed almost worldwide. Most of the Araucariaceae in the Northern Hemisphere vanished in the Cretaceous–Paleogene extinction event, and they are now largely confined to the Southern Hemisphere, except for a few species of Agathis in Southeast Asia.
|Araucaria araucana in Chile|
Henkel & W. Hochstetter
Members of Araucariaceae are typically very tall evergreen trees, reaching heights of 60 m (200 ft) or more. They can also grow very large stem diameters; a New Zealand kauri tree (Agathis australis) named Tāne Mahuta ("The Lord of the Forest") has been measured at 45.2 m (148 ft) tall with a diameter at breast height of 491 cm (16.11 ft). Its total wood volume is calculated to be 516.7 m3 (18,250 cu ft), making it the third-largest conifer after Sequoia and Sequoiadendron (both from the Cupressaceae subfamily Sequoioideae).
The trunks are columnar and have relatively large piths with resinous cortices. The branching is usually horizontal and tiered, arising regularly in whorls of three to seven branches or alternating in widely separated pairs.
Male cones are among the largest among all conifer cones, on average. They are cylindrical and drooping, somewhat resembling catkins. They are borne singly on the tips of branches or the axils of leaves. They contain numerous sporophylls arranged in whorls or spirals. Each has four to 20 elongated pollen sacs attached to the lower surface at one end. The pollen grains are round and do not possess wings or air sacs.
Female cones are also very large. They are spherical to ovoid in shape and borne erect on thick, short shoots at branch tips. The numerous bracts and scales are either fused to each other or separate for half of their lengths. The scales almost always bear only one seed on its upper surface, in contrast to two in true pines (family Pinaceae). They are very large, among the largest seeds among conifers. They are dispersed by wind, usually using wing-like structures. On maturity, the female cones detach and fall to the ground. Due to their size, they can cause serious injuries if they hit a person. The cones of the bunya bunya, Araucaria bidwillii, for example, weigh 10 to 15 lb (4.5 to 6.8 kg), about the size and weight of a large pineapple. They can drop from heights of 23 m (75 ft).
Classification and generaEdit
Araucariaceae is classified under the order Pinales, class Pinopsida of the division Pinophyta. The division includes all living conifers. Recently however, some authorities treat Araucariaceae as a separate order, Araucariales.
- Araucaria Jussieu contains 19 living species found in New Caledonia (where 13 species are endemic), Norfolk Island, Australia, New Guinea, Argentina, Chile, and Brazil.
- Agathis Salisbury contains 21 living species found in New Zealand, Australia, Vanuatu, New Caledonia, Papua New Guinea, Indonesia, Malaysia, and the Philippines
- Wollemia W.G. Jones, K.D. Hill & J.M. Allen contains only one living species endemic to Australia. It was known only from fossil remains before the discovery of the living species in 1994.
Relationships between living members of Araucariaceae.
Distribution and habitatEdit
By far the greatest diversity is in New Caledonia (18 species), with others in Australia, Argentina, New Zealand, Chile, southern Brazil, and Malesia. In Malesia, Agathis extends a short distance into the Northern Hemisphere, reaching 18°N in the Philippines.
Several species 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.
Skillful artisans in the Erzurum Province, Turkey, have used fossilized wood of Araucariaceae for centuries to manufacture jewelry and decorative items. It is known as "Oltustone", the name deriving from the town of Oltu, where it is most commonly excavated. Despite the fact that this semiprecious gemstone is classified as “stone”, wood anatomy reveals it was fossilized pieces of trunks of Araucariacea. Oltustone, also called ‘Black Amber’ is unique to Turkey. It is dull and black, but when polished, acquires an attractive black sheen.
Fossils widely believed to belong to Araucariaceae include the form genera Araucarites (various), Araucarioxylon (wood), Brachyphyllum (leaves), Araucariacites and Dilwynites (pollen), and Protodammara (cones).
The oldest definitive of records Araucaria are Araucaria mirabilis and Araucaria sphaerocarpa from the Middle Jurassic of Argentina and England respectively. The oldest records of the Wollemia-Agathis lineage are Emwadea microcarpa from the Albian aged Winton Formation of Australia and Wairarapaia mildenhallii from the Albian-Cenomanian of New Zealand.
In Arizona, the petrified woods of the famous 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 m tall when they were alive.
The occurrence of Araucariaceae in the Dutlu Formation (Late Cretaceous) Erzurum-Turkey, possibly reflects the southernmost record of the family in the northern supercontinent Laurasia, as well as one of the latest examples ever recorded in southern Eurasia. Araucariaceae possibly grew in forests in the coastal areas of Laurasia which was separated by the Tethyan Ocean from the supercontinent Gondwana.
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