Araucarioxylon arizonicum

Araucarioxylon arizonicum is an extinct species of conifer that is the state fossil of Arizona. The species is known from massive tree trunks that weather out of the Chinle Formation in desert badlands of northern Arizona and adjacent New Mexico and Chemnitz petrified forest in Chemnitz, Germany, most notably in the Petrified Forest National Park. There, these trunks are locally so abundant that they have been used as building materials.
Description.
The petrified wood of this tree is frequently referred to as "Rainbow wood" because of the large variety of colors some specimens exhibit. The red and yellow are produced by large particulate forms of iron oxide, the yellow being limonite and the red being hematite. The purple hue comes from extremely fine spherules of hematite distributed throughout the quartz matrix, and not from manganese, as has sometimes been suggested.
Paleoecology.
In the Triassic period (around ), Arizona was a flat tropical expanse in the northwest corner of the supercontinent Pangaea. There, a forest grew in which "A. arizonicum" towered as high as and measured more than in diameter. Fossils frequently show boreholes of insect larvae, possibly beetles similar to members of the modern family Ptinidae.
Taxonomy.
"Araucarioxylon arizonicum" is classified under family Araucariaceae. They were first described in 1889 by the American paleobotanist Frank Hall Knowlton.
The validity of the name "Araucarioxylon arizonicum" has been questioned. "A. arizonicum" may actually be composed of several different genera and species. A 2007 study on the syntypes used by Knowlton in describing the species has revealed that they belonged to three species. They were tentatively reclassified as "Pullisilvaxylon arizonicum", "Pullisilvaxylon daughertii", and "Chinleoxylon knowltonii". The genus "Araucarioxylon" may thus be superfluous and illegitimate; and the petrified logs of Petrified Forest National Park may be composed of a greater diversity than initially believed.