Rodney A. Savidge (2007). "Wood anatomy of Late Triassic trees in Petrified Forest National Park, Arizona, USA, in relation to Araucarioxylon arizonicum Knowlton, 1889" (PDF). Bulletin of Geosciences. 82 (4): 301–328. doi:10.3140/bull.geosci.2007.04.301.

Here is a brief synopsis of Dr. Savidge's detailed study of petrified wood from this beautiful national park:

There are two major problems with the binomial Araucarioxylon arizonicum, originally named by F.H. Knowlton in 1889 ("New Species of Fossil Wood (Araucarioxylon arizonicum) From Arizona and New Mexico," U.S. National Museum Proceedings 1888 11: 1-4):

1. There were three type specimens deposited in the Smithsonian Institute. According to the International Code of Botanical Nomenclature, a valid species can have only one type specimen or holotype. Consequently, one of the three specimens must be renamed and designated as the new type or lectotype.

   Lectotype: Specimen later selected to serve as definitive type when the original author of the name did not designate a legitimate holotype. This applies to illegitimate name Araucarioxylon arizonicum because a new type must be selected even though original type was not lost. If the original type specimen (holotype) was lost, a new type called neotype must be selected and the process is called neotypification. If a neotype is once again neotypified the process is called re-neotypification! I was personally involved with the following controversy:

   Very Complicated Duckweed Controversy Involving Proposed Re-Neotypification!

2. The original three type specimens represented three different species.

I planned to use some of my images from Petrified Forest National Park in my article for Pacific Horticulture entitled "The Araucaria Family: Past and Present." However, I am not sure which of the logs (if any) are related to the araucaria family. Based solely on the xylem structure of permineralized wood (including resin canals, rays and tracheid pitting), and without seed cones or DNA evidence, it is difficult to be certain which trees in the complex are ancestral relatives of the Araucariaceae. Trees of "Araucarioxylon arizonicum" supposedly grew to a height 200 feet (61 m) with a trunk diameter from 4 to 9 feet. According to Sidney R. Ash and Geoffrey T. Creber ("The Late Triassic Araucarioxylon arizonicum Trees of the Petrified Forest National Park, Arizona, USA," Paleontology Vol. 43 No. 1: 15-28, 2003), the living tree did not closely resemble any of the present-day Araucaria trees of the southern hemisphere as postulated in past reconstructions. The branches did not occur in whorls as they do in most conifers, instead they grew irregularly along the trunk. Sydney Ash and Rodney Savidge also studied the bark anatomy of Araucarioxylon arizonicum ("The Bark of Late Triassic Araucarioxylon arizonicum from Petrified Forest National Park, Arizona," IAWA Journal 25 No. 3: 349-368, 2004), and concluded that it was quite unlike the banded bark of extant Araucaria heterophylla.