What’s in a Name? The Araucarioxylon Problem

Petrified Wood Layers in Petrified Forest National Park

NPS

One question we receive over and over again at Petrified Forest National Park is: “What kind of trees were the logs?” The easiest response is that the trees were a type of gymnosperm as there were no angiosperms at the time. Some people are willing to accept this, but others persist. The next response is that the trees were conifers and gingkoids, again, some are satisfied, but others are not. This problem will continue forever as many of the petrified logs are so agatized that the microscopic details of their structure are totally obliterated. The old name of Araucarioxylon arizonicum is pretty much out.

The park paleontologist comments that every single log would have to be thin sectioned and that sample examined microscopically to determine its genus and species as you just can’t tell with the naked eye. Identification of the tree species requires microscopic examination of thin sections of the xylem tissue. 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 park are related to what living trees in our world. Some have suggested that the name “Agathoxylon” be used, but eventually that name will experience the same issues as Araucarioxylon.

We currently recognize 14 different species of wood in the park and there were probably many more. To date we have recovered wood from nine different geologic levels in the park with millions of years separating these layers. No doubt over time the types of trees in the environment changed.

All of our recent wood work has been done by Dr. Rodney Savidge of the University of New Brunswick. He is currently studying more samples that the park paleontologist has collected and sent to him from the various geological levels.

Websites on the Araucarioxylon problem:
http://waynesword.palomar.edu/pfnp.htm
http://chinleana.blogspot.com/2011/01/agathoxylon-wood-morphogenus-previously.html

Some of the recent tree species in the park named by Dr. Rodney Savidge:
Pullisilvaxylon arizonicum
Pullisilvaxylon daughertii
Chinleoxylon knowltonii