Brachyoxylon cristianicum Iamandei, Iamandei and Grădinaru, 2018

Iamandei, Stanila, Iamandei, Eugenia & Grădinaru, Eugen, 2022, Contributions To The Study Of The Early Jurassic Petrified Forest Of Holbav And Cristian Areas (Brașov Region, South Carpathians, Romania), 2 Part., Acta Palaeontologica Romaniae 18 (1), pp. 25-48 : 33-35

Brachyoxylon cristianicum Iamandei, Iamandei and Grădinaru, 2018

Fig. 4 , a-i.

Material

The studied material is represented by 13 samples of silicified wood collected from the Holbav locality, on Maiului brook. All the studied samples are fragments of trunk or thick-branch fragments, with centimetric to decimetric size, dark color and, by hand lens or even naked eye, the regular fibrous structure without vessels is visible, evidence of a conifer wood. The specimens, with the following field numbers: 1071, 1072, 1073, 1075, 1076, 1080, 1081, 1101, 1103, 1108, 1110, 1112, 1113b belong to “Grădinaru Collection” and are stored at the National Museum of Geology , in Bucharest, under the inventory numbers 27678, 276789, 27680, 27681, 27682, 27684, 27685, 27686, 27717, 27687, 27688, 27689, 27690 .

Microscopic description

Growth rings – in cross-section show a tracheidoxylic structure without resin canals, usually with abrupt transition from early- to late-wood, and with rather distinct growth-ring boundary. Resin canals absent.

Tracheids – with polygonal (quadrangular) cross-section with rounded corners, unequal in size, diameters of 20- 35-(45-65) μm and with thick walls, of 5-8(9) μm the double wall, usually curled by compression. The late-wood is represented by 2-3 rows of thick-walled and radially flattened cells (radial diameter of 5-10 μm). Intercellular spaces are present. The interradial bundles have 1-10 radial regular rows of tracheids. Density is of 992- 1518 tracheids per mm 2. Tangential pitting is absent. Radial pitting is usually uniseriate or biseriate of mixed type. When biseriate, the pits appear alternate or opposite and contiguous on short rows often continued by uniseriate portions and do not occupy all the length of the wall. The pits have round to hexagonal borders, diameters of 18-22 μm, and are variably flattened when contiguous (d/D=0.65-0.88), bearing round or tilted elliptic apertures of 7.5-10 / 2-3 μm. Sometimes crassulae or helical thickenings can appear.

Axial parenchyma – in cross-section appear few, dispersed, often difficult to identify among the tracheids. Vertically, sometimes they can show simple pits. The horizontal walls are thin and smooth, or slightly nodular. Sometimes, a resin content is present inside the cells, as plugs or granules.

Rays – in cross-section appear usually uniseriate and linear. In tangential section, the rays show 1-20(-25) cells in height (i.e. 30-570(-650) μm). The taller uniseriate rays have biseriations, which give sometimes a fusiform aspect. The ray-cells have polygonal rounded to oval section, marginal spaces and sometimes have dark content. The ray density is of 5-11 rays per horizontal millimeter. The rays appear homogeneous, with cells all procumbent, of 20-30 μm tall, relatively thick walled, of 4-5(7) μm the double wall. Within the marginal rows, but not only, the ray cells are taller, of 30-40 μm, and have slightly corrugated outer walls. The cross-fields are of araucarioid type, have 1-6(-8) pits, hexagonal or slightly rounded to oval, of cupressoid type, tending to podocarpoid or araucarioid. They have 15-19/8-12 μm in diameters, and show circular or short elliptic tilted apertures of 10-14/5-7 μm. The pits are arranged in 1-2(3) rows per cross field, within ray body fields, or in the marginal fields and are alternate to slightly irregular.

Resin canals – are absent.

Mineral inclusions – are absent.

Affinities and discussion

From the microscopic study of all the standard oriented thin sections, we selected 13 specimens having similar generic characters, represented by tracheidoxylic structure, radial pitting of mixed type on tracheids and araucarioid cross-fields, which are consistent with the structure of Brachyoxylon wood-type (see Philippe, 1993; Philipe and Bamford, 2008), but a slightly different from the above-described species.

We do not repeat the discussion from above on the genus creation and about the previously described species, but, consulting the comparative Table 1, from Iamandei et al. (2018), we observed beside the generic characters some other specific details that are different of those of the above-described species.

Thus, we observed that the radial tracheidal pitting of mixed type are commonly discontinuous, the axial parenchyma is present, as dispersed cells with slightly nodular horizontal walls and with resin content inside.

Other features are: the relatively tall uniseriate rays with biseriations, up to fusiform aspect, homogeneous and with cross-fields with 1-6(-8) hexagonal to rounded cupressoid oculipores, alternately arranged (araucarioid) to slightly irregular. All these details almost identical to those of the species Brachyoxylon cristianicum , which was previously described from the same area ( Iamandei et al., 2018).

From these characteristics, we attribute all the 13 here studied specimens coming from Holbav and Cristian to the above specified form: Brachyoxylon cristianicum Iamandei, Iamandei and Grădinaru, 2018 .

Figures

Fig. 4 Brachyoxylon cristianicum Iamandei, Iamandei and Grădinaru, 2018 - inventory no. 27690(field no. 1113b). a-c: Cross section - thick-walled tracheids, polygonal, with rounded corners and curled walls; dispersed parenchyma cells; linear rays; d-f: Tangential section - uniseriate rays with polygonal ray-cells and biseriate storeys; unpitted tracheids; parenchyma with end-walls smooth or nodular and resin content inside; g-i: Radial section - radial pitting on tracheids of mixed type; cross-fields with 2-3 cupressoid or araucarioid in a single row or, when more numerous, in 2-3 superposed rows.