Araucariaceae: systematics
Araucariaceae is the most primitive of extant conifers. Popular species such as the pine are thought to have derived from Araucariaceae. There are a few important features that separate Araucariaceae from other conifers. The leaves of Araucariaceae are very broad as opposed to the usual needles found on many conifers. There is no distinct mid-vein in Araucariaceae leaves. The wood also has very characteristic tracheids with several rows of bordered pits as opposed to the one or two rows in other conifers. The male cones of Araucariaceae are also distinctly larger (up to 15cm!) than most conifers. The pollen is also distinct from other conifers because it is wingless. The female cones are also fairly distinct in having a fused bract and scale with the ovule sitting on top of the scale, whereas the scale and bract in other conifers are separate.
Distinguishing Factors Defining between Agathis, Araucaria, and Wollemia
Agathis is distinguished by larger leaves and by the seed being free from the scale. Agathis has one developed wing on the seed, and in Araucaria the seed is combined with the scale, which is usually winged on the edges. The branches in Agathis fall off later than in Araucaria, and the leaves are more sparse in Agathis. The male cone in Agathis is smaller than in Araucaria. Wollemia differs from both genera in that it has a spongy nodular bark, which sheds in papery scales. It also differs in that it has terminal male and female cones on first-order branches. Wollemia's differences will become more apparent and its placement will become more defined as more studies are conducted on this new discovery.
Agathis and Araucaria have each about 21 species, and there is 1 species in Wollemia. The one specie of Wollemia is one of the rarest extant trees know to us today.
