West of Gokwe in Zimbabwe, Africa a 30km wide
Triassic aged forest is exposed to the surface (Dernbach, 1996,
of Araucarioxylon, Woodworthia, and Rhexoxylon can be found
(Daniels and Dayvault, 2006, p. 119). Popular among collectors
specimens with a green coloration. This green coloration is
created by the presence of chromium compounds (Daniels and
2006, p. 175).
Araucarioxylon is the wood of a conifer that is represented
in many of the forests of the Triassic and Jurassic (Tidwell,
1998, p. 206). Fossil wood assigned to this genus is though
to be related to members of the Araucariaceae family. The genus
is derived from the name of a tribe indigenous to the Andes
of South America. The Incas used arauco to describe any tribe
that remained unconquered (Dernbach, 1992, p. 14). Present
day well known araucaria are cultivated in the Southern Hemisphere.
These include the Norfolk Island Pine (Araucaria heterophylla),
Araucaria bidwilli, and Araucaria brasiliensis.
When looking at a cross-section of araucaria with a 10x loupe
one can clearly see the trachieds that make up the xylem. One
can also note the absence of resin canals. Dadoxylon may also
be an araucaria fossil wood. Traditionally, araucaria from
the Paleozoic was refered to as Dadoxylon, while araucaria-like
wood from the Mesozoic was assigned the genus Araucarioxylon (Derbach, 1992, p. 127). Most collectors of these fossil woods
consider them to be different species regardless of the time
period assigned. The collector identifies Dadoxylon with pith
that has distinct serrations formed by the primary xylem centers
of growth (Dernbach and Tidwell, 2002, p. 129). In some specimens
the pith can exhibit a star-shaped pattern.
Woodworthia is the wood of an araucarioid with numerous leaf
and shoot traces, which can be seen both in cross-section and
on the outer surface of well-preserved specimens.
Rhexoxylon, in cross-section, would remind one of Pentoxylon or Hermanophyton. Rhexoxylon has similar wedges of secondary
xylem, which surrounds pith that contains anomalous growth
and Rhomboidal-shaped leaf bases on the outer surface of the
stem. The wedges of xylem are very interesting in that they
have growth centers that produced wood towards the inside pith
as well as to the outside (Dernbach and Tidwell, 2002, p.199).
Rhexoxylon may represent an arborescent seed fern.
Daniels, F.J. and Dayvault, R.D. 2006. Ancient Forests: A Closer Look at
Fossil Wood. Western Colorado Publishing Company: Canada.
Dernbach, U. and Tidwell, W.D. 2002. Secrets of Petrified
Plants: Fascination from Millions of Years. D’ORO:
Dernbach, U. 1996. Petrified
Forests: The World’s 31
Most Beautiful Petrified Forests. D’ORO: Germany.
Dernbach, U. 1992. Araucaria.
Tidwell, W.D. 1998. Common Fossil Plants of Western North
America. [2nd Edition]. Smithsonian Institution Press: Washington,