Brachyoxylon sp.

Uhl, Dieter, 2004, Anatomy and taphonomy of a coniferous wood from the Zechstein (Upper Permian) of NW-Hesse (Germany), Geodiversitas 26 (3), pp. 391-401 : 394

? Brachyoxylon sp. ( Figs 2 ; 3 ; 4 A-E)

DESCRIPTION

A fragment of partly pyritized wood, possibly originating from a small trunk or a branch, without cortex. In radial longitudinal view tracheids are 20-30 µm wide. Tracheids exhibit uniseriate bordered pits on the radial walls. Pits circular (to elliptical) (18-25 µm diameter) with circular or oval apertures and often contiguous (then flattened) and sometimes spaced more than one pit diameter apart. In some areas, tracheids occur which seem to have spirally thickened cell walls. Rays very scarce and composed of parenchymatous cells, 25-35 µm long and 20-30(50) µm high. Rays uniseriate and 2-4 cells high. Crossfield pitting very badly preserved, but probably araucarioid consisting of 1-4(?) alternately arranged circular pits per field. No growth rings visible. Pith of a twig or small branch(?) 200- 250 µm wide, consisting of parenchymatous cells, 20-80 µm wide. In an area, probably representing a small branch or a leaf trace, tracheids and rays are arranged irregularly. In this area, bordered pits occur on tangential tracheid walls and rays can be seen in tangential view.

REMARKS

This is the first record of a wood with a “mixed” type of pitting (araucarioid and abietoid) from the Upper Permian of the euramerican floral province. This type of pitting is diagnostic of woods of the Protopinaceae (e.g., Vogellehner 1967, 1968; Müller-Stoll & Schultze-Motel 1989), a phylogenetically artificial group with mainly Mesozoic occurrence. Taken all characters together, the wood described here shows great similarities to the protopinacean form-genus Brachyoxylon (cf. Bamford & Philippe 2001). However, an important character for such an assignation is the type of cross-field pitting (cf. Bamford & Philippe 2001). Although the crossfield pitting is very poorly preserved in this specimen it seems to be of the araucarioid type. Therefore this wood is here only provisionally identified as? Brachyoxylon sp.

Despite the type of pitting on the radial tracheid walls, the wood described here shows great similarities with the wood of the conifer Pseudovoltzia liebeana (Geinitz) Florin , which has been described by Schweitzer (1962) based on a 2 mm thick axis from the Zechstein of the Lower Rhine (W-Germany). Unfortunately, Schweitzer (1962) gave no quantitative data concerning the measurement of the individual anatomical details. The only measurements given by Schweitzer (1963) come from a cone axis of Pseudovoltzia liebeana and can probably not be compared with wood originating from a stem or even large twig. However, Schweitzer (1962) could not find any significant differences between the wood of this taxon and other Upper Permian conifer taxa from the same area (see also Table 1). Due to the poor preservation and scarcity of fossil woods from the Zechstein of the Lower Rhine area, Schweitzer (1962) could not describe these woods in great detail and several important characteristics are still not known for most of the woods described by this author ( Table 1). Therefore it is not yet possible to assign the wood described here to any of the known conifer taxa from the Zechstein. Lemoigne & Schaarschmidt (1968) were able to give a more detailed description of the wood of the conifer Ulmannia bronnii Göppert than Schweitzer (1962). Their description, which was based on the wood of a small, partly pyritized shoot with attached needles from Frankenberg-Geismar, does not match this wood. In contrast to the wood described here, these authors observed abundant rays and they reported that the always contiguous, bordered pits were not only arranged uniseriately, but also biseriately. Though we cannot exclude that these differences are due to positional variations within a single plant, a unification of the wood described here with this taxon is absolutely not justified. However, some details (scarcity of rays, dimen- sions of tracheids, uniseriate arrangement of pits) of this wood are similar to “woodtype 5”, described by Uhl & Kerp (2003) based on charcoalified material from the same locality. However, both modes of preservation differ too much to allow a certain unification of both types of wood.

Figures

FIG. 2. —?Brachyoxylon sp. from the Zechstein (Upper Permian) of Frankenberg-Geismar (NW-Hesse); A, complete specimen in tangential view; B, complete specimen in perpendicular view; C, radial section, showing pyritized and non-pyritized areas with anatomical preservation (Pb-WB-H-1/d); D, cross-section, showing pyritized and non-pyritized areas with anatomical preservation (Pb-WB-H-1/a);E, radial section,showing details of the central pith (Pb-WB-H-1/b).Scale bars: A, 3 cm;B, 2 cm; C, D, 1 mm; E, 200 µm.

FIG. 3. —?Brachyoxylon sp. from the Zechstein (Upper Permian) of Frankenberg-Geismar (NW-Hesse); A, cross-section, showing cracks filled with pyrite (Pb-WB-H-1/a); B, radial section, showing “spirally thickened” (probably checked during desiccation) tracheid walls (arrows) (Pb-WB-H-1/d); C, radial section, showing remains of a ray (arrow) with very poorly preserved cross-field pitting (Pb-WB-H-1/d); D, radial section, showing uniseriate, circular bordered pits (arrow) (Pb-WB-H-1/d). Scale bars: A, 1 mm; B, 150 µm; C, D, 100 µm.

FIG. 4. — A-E,?Brachyoxylon sp. from the Zechstein (Upper Permian) of Frankenberg-Geismar (NW-Hesse); A, radial section, showing the central pith, flanked by cracks filled with sediment (Pb-WB-H-1/b); B, radial section, showing remains of a branch(?) (Pb-WB- H-1/b); C, detail of B, showing tracheids and rays adjacent to the branch(?) (Pb-WB-H-1/b); D, cross-section, showing cracks filled with sediment (Pb-WB-H-1/a); E, radial section, showing cracks filled with sediment (Pb-WB-H-1/b); F, G, charcoal from the Zechstein (Upper Permian) of Frankenberg-Geismar (NW-Hesse), exhibiting checked cell-walls, resulting from desiccation prior to charring. Scale bars: A, 500 µm; B, 1 mm; C, 100 µm; D, E, 1 mm; F, 90 µm; G, 30 µm.