Thujoxylon sp.

Iamandei, Stanila, Iamandei, Eugenia & Todea, Petru, 2020, Palaeoxylotomical Study Of A New Collection From Zarand Miocene Petrified Forest, South Apuseni Mts., Acta Palaeontologica Romaniae 16 (1), pp. 19-34 : 19-22

Thujoxylon sp.

Fig. 1 , a-i; Fig. 2 , a-i.

Material

Two samples of petrified wood collected from South Apuseni mts., Ociu area, Bisericii brook, from Mid-Miocene deposits (late Badenian-early Sarmatian), kept now in “ Todea Collection ”, in Crișcior- Brad locality, under the indicative OB-4 and OB-5 , both with standard oriented thin sections prepared, were submitted to the paleoxylotomical study.

Microscopic description

The growth rings are relatively wide, of 36-60 cells, with distinct boundaries, since the late wood is represented by 5-7 tangential rows of radially flattened and thick-walled cells, disperse few parenchyma cells often with black content. Normal resin canals are absent.

The tracheids, in the early-wood, are big, quadrangular or polygonal shaped, or slightly elongate, and are relatively thin-walled (4-6 μm the double wall). Their lumina have slightly rounded corners, and radial / tangential diameters of 25-35 / 20-30 µm, gradually diminishing through transitional 6-8 tangential rows of smaller lumened cells to the latewood, where they appear in 8-12 tangential rows of small, quadrangular, radially crushed and very thick-walled cells, of 8-12 μm double wall, and with r / tg diameters of 10-15/8-15 µm. There are 1-9 radial rows between two rays and the density is of 1900-2025 tracheids on sq. mm. The tangential tracheidal walls seem to be pitted, with small and spaced pits. The radial abietineous pitting is uniseriate, spaced or nearly contiguous and probably with crassulae, difficult to see due to bad preservation. The bordered pits are relatively small (8-12 µm the diameter), with round aperture, of 3-5 µm in diameter.

The axial parenchyma seems to be absent, or rare, or difficult to observe in cross-section, since is quite similar to the tracheids. However, it is obvious in tangential view, having horizontal nodular walls, and presenting glomeruli of resin inside, or plugs with round concavities.

The rays are uniseriate, not too high, of up to 8-12 cells. Radially the rays seem to be homogeneous and are constituted from cells of 12-14 μm taller marginals and with waved outer walls. No details on the inclined walls have been observed. Indentures probably present, difficult to observe due to bad preservation. In the cross-fields, 1-2 small round to oval, small, badly preserved cupressoid or taxodioid pits of 5-6 μm in diameter, horizontally arranged or in vertical pairs in the late-wood cross-fields, having rounded lens-like, inclined to vertical apertures. In the marginal cross fields 2-4, as superposed pairs of round pits are present.

Affinities and discussions

The palaeoxylotomical observations made on the studied specimens suggests, by the aspect of the structure in cross section, devoid of resin canals, with few parenchyma having horizontal nodular walls and cupressoid cross-fields with typical aspect of a cupressaceous structure of Thujidae group, especially of Thuja type, even if some badly preserved details do not allow identifying a species. The identification key of Vaudois & Privé (1971) explain that the cupressaceous structures have “zones d’acroissement distinctes, tracheides a ponctuations radiales abietineénnes uniseriées, parenchyme absent ou rare, a parois transversales noduleuses ou ponctuées, rayons généralement peu élevés, uniseriés, parfois biseriés sur un faible hauteur; champs de croisement contenant 1-4 ponctuations taxodioides, parfois cupressoides, indentures présentes” for Thuja type structure. The Chamaecyparis type has a lot of parenchyma and the Juniperus type has specific juniperoid nodules on the inclined tangential walls of ray cells in tangential view, details not observed in our specimens.

The fossil morphogenus, initially variably spelled as Thuyoxylum-Thuoxylon-Thuioxylon-Thuyoxylon, was correctly spelled as Thujoxylon by Hartig in 1848 (see Andrews, 1955, p. 251; Dijkstra & van Ameron, 2002).

Numerous morphospecies were described, in time (see also Vaudois & Prive, 1971 revising the Cupressaceous fossil lignotaxa). Between the last described species, we cite Thujoxylon antissum Süss & Velizelos, 1998 , described from Lesvos, Greece, a tertiary form representing root-wood with a special pattern of growth rings and cross section. The species was quoted and discussed again by Mantzouka et al. (2013). Also, a Cretaceous species named Thujoxylon beipiaoense Ding et al., 2016 , having similar features, was described from China.

Pretty badly preserved specimens were described from Romanian extra-Carpathian area as Cupressinoxylon sp. aff. Thujoxylon sp. ( Iamandei et al. 2008, 2011, 2012).

Anyway, taking into account the papers of Greguss (1967), Dupéron-Laudouéneix (1979), Zalewska (1953), the revised diagnoses of Kräusel (1949) and Vogellehner (1967, 1968), and using the key of identification proposed by Vaudois et Privé (1971), we assign our studied specimens to Thujoxylon sp. , and no more, due to bad preservation of the studied material.

Figures

Fig. 1 a-i (graphic scale, μm). Thujoxylon sp., Ociu, Bisericii brook, South Apuseni, Romania, sample OB-4. a-c. (cross section) – distinct growth rings, earlywood and latewood tracheids, few parenchyma dispersed, uniseriate rays; d-f. (tangential section) – uniseriate short rays, parenchyma with nodular horizontal walls and resin content; g-i. (radial section) – uniseriate pitting on tracheids, 1-2 round pits in cross-fields, in vertical and also horizontal pairs.

Fig. 2 a-i (graphic scale, μm). Thujoxylon sp., Ociu, Bisericii brook, South Apuseni, Romania, sample OB-5. a-c. Cross section – distinct growth rings, early-wood and late-wood tracheids, disperse parenchyma, uniseriate rays; d-f. (tangential section) – uniseriate short rays, parenchyma with nodular horizontal walls and resin content with round empty spaces and thick terminal walls; g-i. (radial section) – uniseriate pitting on tracheids, 1-2 round pits in cross-fields, vertical pairs also.