Araucarian pine,  A.L. Jussieu 1789
Araucariaceae

Araucaria - Araucarian pine description

Short to tall evergreen trees. Trunk usually single, straight, and slender to massive, with little taper beneath the crown. Bark thin to irregularly corky, often with horizontal lines of lenticels and enlarging persistent leaf bases when young, remaining smooth with age or peeling and flaking and becoming scaly and roughened and sometimes even moderately ridged and furrowed. Resin canals absent, but sometimes with scattered, individual resin-filled tracheids. Crown generally open, often becoming strikingly flat-topped with age either moderately shallow because of the shedding of lower branches or extending practically to the ground because such shed branches are replaced from adjoining buds on the trunk, such crowns (as in Araucaria columnaris) being narrowly cylindrical. Branches arranged in regular pseudowhorls, typically turned up at the ends, the lower ones sometimes pendulous. Branchlets all elongate, without distinction into long and short shoots, attached directly to the primary branches, often just out to the sides, but sometimes all around, elongating but usually not themselves branching further, coarse to very thick, remaining, green for several years until shed by themselves or  with the supporting branch. Resting buds unspecialized, without distinct bud scales. Leaves crowded, spirally attached, rarely (Araucaria bidwillii) somewhat two-ranked, stiff, clawlike to scalelike and slightly flattened top to bottom or side to side (in the 15 species of section Eutacta) or spearheadlike (in sharpness as well as in shape) and flattened top to bottom (in the four species in the remaining three section).

Plants monoecious or occasionally dioecious. Pollen cones single (or in small clusters) at the tips of branchlets or in leaf axils or at the end of short side shoots, cylindrical, to 22 cm long. Each pollen cone with a few sterile scales at the base of numerous, densely spirally arranged pollen scales. Pollen scales with a more or less triangular exposed blade at the end of a very slender stalk that is surrounded by some 4-20 elongate cylindrical pollen sacs attached only at one end to the base of the scale head. Pollen grains large to very large (50-100 μm in diameter), nearly spherical and generally featureless. Seed cones solitary and upright at the ends of branches, large, often nearly spherical, to 25 cm wide, some among the most massive of conifer seed cones, ripening in 2-3 years, then disintegrating. Seed scales fused to the bract for half or more of their length, leaving a slot between the two in the outer portion, very numerous (often in the hundreds), densely overlapping, thickened at the tip, often winged at the sides, the bract prolonged as a narrowly triangular point. Each seed scale with a single, large seed (some the largest among conifers) without wings and embedded in a depression in the seed scale, in which they are retained and fall with the scales from the shattered cones. Cotyledons two, each with two veins, or four cotyledons, each with one vein. Chromosome base number x = 13.

Wood soft and weak, of medium weight, with nearly white to yellowish sapwood not very distinct from the similar or slightly darker white to light brown heartwood that is sometimes streaked with darker brown or red. Grain very fine and even, usually with little or no evidence of growth rings, but sometimes with a few slightly flatter, thicker-walled latewood tracheids.

Stomates in a few to many regular (or somewhat irregular and interrupted) longitudinal lines (which may be arranged in bands or patches) on both the upper and lower surfaces (often nearly restricted to the lower surface in Araucaria bidwillii). Individual stomates highly varied among different species, sunken beneath and partially hidden by the one to three circles of four to six often crinkly walled subsidiary cells, the inner circle lacking a Florin ring but plugged with wax. Leaf cross section with a single midvein (clawlike and scalelike leaves) or with additional smaller veins paralleling it on either side (broader leaves),  at least the midvein flanked by some transfusion and sclerenchyma tissue. Epidermis underlain by an often multilayered hypodermis everywhere except next to the lines of stomates. Photosynthetic tissue consisting of a more or less well defined palisade layer on the upper side (and sometimes on the lower as well) and looser spongy mesophyll beneath the palisade. Resin canal usually single, centered under the midvein or sometimes with others off to the sides of the leaf and above the midvein.

Nineteen species in New Guinea, Northeastern Australia, Norfolk Island, New Caledonia, and southern Brazil to Chile.

The majority of species of Araucariaare tall rain-forest emergent, with massive columnar trunks carrying their canopies to 30-60 m (or even 89 m in Araucaria hunsteinii) above the forest floor. Many are important timber trees, or were before their stands were depleted. Species with the largest seeds, like Araucaria araucana, Araucaria bidwillii, and Araucaria brasiliensis, have also been important seasonal food resources for local people living in the vicinity of stands. In fact, the name Araucaria is the common name of monkey puzzle tree (Araucaria araucana) used by one of these peoples, the Araucanians of Chile. Two-thirds of the species are restricted to New Caledonia, where they occur primarily on serpentine soils. Few of these are in cultivation and all species on the island belong to section Eutacta, the largest of the four sections. A handful of species are widely and extensively cultivated, with Araucaria heterophylla and Araucaria bidwillii (Bunya-bunya) in the tropics and Araucaria araucana extending into cooler but still mild regions, like southern coastal British Columbia in Canada, and with Araucaria heterophylla also produced in millions as a house plant. Despite this there has been virtually no cultivar selection in the genus.

The living section from an almost continuous series in their distinguishing characteristics, even with respect to microscopic features (Stockey and Ko 1986). Nonetheless, there is reasonable paleobotanical and phylogenetic justification for recognizing the sections, and they are retained here also as a convenient first division in the identification guide. Were it not for fossil record, the three smaller sections (sections Araucaria, Bunya, and Intermedia), containing only four extant species among them, might well be merged into a single section that would be called section Araucaria because it contains the type of the genus, monkey puzzle tree (Araucaria araucana).

DNA studies reveal little genetic divergence among the New Caledonian species, implying that the taxonomic and ecological diversity of this group has been the result of a relatively recent radiation rather than relictual retention of ancient species that might have been anticipated from the long fossil record of the genus.

It is uncertain when Araucaria first evolved, but Araucarian seed scales that could belong to the genus first appeared in Eurasia, North America, and the then Gondwanan India in the late Triassic, more than 200 million years ago. Even earlier, in the Paleozoic, the earliest known conifers had foliage and growth habits remarkably similar to those of some extant araucarias, such as Norfolk Island pine (Araucaria heterophylla) and other species of section Eutacta, but their cone structures are not araucarian and they were presumably the ancestors of all extant conifers, not just Araucaria. Undoubted members of the genus had an essentially worldwide tropical distribution throughout the remainder of the Mesozoic, after which they became extinct in the northern hemisphere and progressively restricted to their present distribution in the southern hemisphere during the Tertiary. The fossil record contains some morphological features not found among the extant species so that additional taxonomic sections were named just for extinct species.

References

• Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
• Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
• IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.