Araucariaceae

Araucariaceae – also known as araucarians – is an extremely ancient family of coniferous trees. The family achieved its maximum diversity during the Jurassic and Cretaceous periods and the early Cenozoic, 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.

Description

Members of Araucariaceae are typically extremely tall evergreen trees, reaching heights of 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 tall with a diameter at breast height of . Its total wood volume is calculated to be , 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.

The leaves can be small, needle-like, and curved, or they can be large, broadly ovate, and flattened. They are spirally arranged, persistent, and usually have parallel venation.

Like other conifers, they produce cones. Each tree can have both male and female cones (monoecious) or they can have only male or female cones (dioecious).

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 , about the size and weight of a large pineapple. They can drop from heights of .

Classification and genera

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.

Araucariaceae contains three extant genera and about 41 species.

Phylogeny

Below is the phylogeny of the Pinophyta based on cladistic analysis of molecular data. It shows the position of Araucariaceae within the division.

Relationships between living members of Araucariaceae.

Molecular evidence supports Araucariaceae and Podocarpaceae having diverged from each other during the late Permian.

Distribution and habitat

Today, 41 species are known, in three genera: ''Agathis'', '' Araucaria'' and ''Wollemia'', 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 Brazil, and Malesia. In Malesia, ''Agathis'' extends a short distance into the Northern Hemisphere, reaching 18°N in the Philippines.

Uses

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.

Fossil record

Fossils widely believed to belong to Araucariaceae include the form genera ''Araucarites'' (various), ''Agathoxylon'' and ''Araucarioxylon'' (wood), ''Brachyphyllum'' (leaves), '' Araucariacites'' and '' Dilwynites'' (pollen), and '' Protodammara'' (cones).

The oldest definitive records of Araucariaceae are from the Early Jurassic, though there are potential earlier Late Triassic records. Early representatives of ''Araucaria'' are widespread across both hemispheres by the Middle Jurassic, such as ''Araucaria mirabilis'' and ''Araucaria sphaerocarpa'' from the Middle Jurassic of Argentina and England respectively. The oldest records of the ''Wollemia''-''Agathis'' lineage from the Cretaceous, including '' Emwadea microcarpa'' from the Albian aged Winton Formation of Australia and '' Wairarapaia mildenhallii'' from the Albian-Cenomanian of New Zealand. The oldest fossils currently confidently assignable to ''Agathis'' are those of ''Agathis immortalis'' from the Salamanca Formation of Patagonia, which dates to the Paleocene, approximately 64.67–63.49 million years ago. ''Agathis''-like leaves are also known from the slightly older Lefipán Formation of the same region, which date to the very end of the Cretaceous.

See also

*Paleobotany
*Te Matua Ngahere

References

Further reading

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{{Authority control

Pinales families
Extant Hettangian first appearances
Araucariales