Thujoxylon sp.

Iamandei, Stănilă & Iamandei, Eugenia, 2017, New Trees Identified In The Petrified Forest Of Middle Miocene From Zarand, Apuseni Mountains, Romania., Acta Palaeontologica Romaniae 13 (2), pp. 37-90 : 43

Thujoxylon sp.

Fig. 5 , photos a-i.

Material

From a sample of petrified wood collected from North of Ociu area, on OciȘor brook, of Mid- Miocene volcano-sedimentary deposits (Late Badenian-Early Sarmatian). The sample has brown color and centimetric size, fragmented after oriented slides cut, and is kept now in GIR Collection at National Geological Museum - Bucharest under the inventory number 26,441 (724 as field number).

Microscopic description

Growth rings distinct, of 75-121 tracheids high, with gradual transition from early to late wood. The ring boundary is marked by 6-12(18) thick walled cells of late wood. Normal axial ducts are absent.

The tracheids have a polygonal cross section, with rounded corners. Between two successive rays there are 1-11 regular radial rows of tracheids, sometimes with intermingled rows of smaller tracheids. Usually the tracheid sizes vary between 20-48 / 20-48 μm the radial / tangential diameters, smaller in the late wood. The wall thickness is of 4-6 μm double walls, thicker in the late wood, up to 8-12 μm. The density is 1692-2116 tracheids per mm 2. On the tangential walls the pitting is uni- or biseriate, with pits spaced or contiguous or slightly irregularly arranged, with badly preserved round borders of 12- 15 μm in diameter, to which often only the chamber is visible, round to oval of 4-6 μm giving a false "taxodioid" aspect, and with elliptic vertical apertures of 2-4 μm when visible. On the narrower tracheids the uniseriate pits are circular, of abietinean type of 8 μm in diameter and apertures of 3.5-4 μm. The radial pitting is clearly of abietinean type, spaced or contiguous arranged in 1 or 2 vertical rows, when are opposite and with crassulae. The pits have round borders of 15-19 μm in diameter and round apertures of 4 μm in diameter. The pit chamber seems to be of vestured type (ornamented), has up 11-12 μm in diameter and is well preserved. The tangential walls are slightly molding the pits row, gaining a wavy appearance.

The axial parenchyma is absent.

The medullary rays are rectilinear in cross section, uniseriate in tangential view of (3)6-22(36) cells high, sometimes with 1-3 biseriate storeys isolated or grouped. The ray cells are square-rounded to vertical elliptic, of 12-20 μm in diameters, some of them irregularly simple pitted (sieved) or filled of resinous content. Lateral intercellular spaces are absent. Their frequency is of 5-7 rays on tangential millimeter. Radially the rays are homocellular, with cells all procumbent having 16-20 μm in height, the marginals taller, having 20-28 μm. The horizontal walls are smooth, slightly pitted and relatively thick, of 4 μm double wall. The tangential wall has 1-3 μm (simple wall), is smooth or slightly rugose, straight, inclined or arched and the indentures are indistinct. Cross-fields badly preserved have 1-2 cupressoid pits, rounded, of 4-5 μm in diameter, with round to elliptic inclined apertures of 1- 2 μm. The pair- pits are horizontally arranged or slightly diagonal. In the marginal fields 2-5(6) similar pits appear, in 2 rows arranged.

Affinities and discussions

The essential xylotomic characters shown by the studied specimen are very similar to those of Cupressaceae family: tangential pitting uniseriate or biseriate and slightly irregular, pits smaller, radial pitting 1-2 seriate, typically abietinean, axial parenchyma absent, ray cells generally circular and cupressoid pitting in cross fields (see Greguss, 1955). All these details suggest a cupressaceous structure of extant "Thujidae Group", especially of Thuja type, even if there are similitudes also with other members of the group as Microbiota , Chamaecyparis or Biota . All these genera belong now to the Subfamily Cupressoideae Rich. ex Sweet ( Farjon, 2005) .

Evaluating the combination of the xylotomical details of our specimen we observe similitudes with those specified in the diagnosis reformulated after previous authors (as Unger, Pierce, Penny, Beyer, Jacquiot and Greguss), cited by Vaudois & Privé (1971, p. 65-66), who made an identification key which explain that these 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.

They specified also that Chamaecyparis type has a lot of parenchyma, since Juniperus type has specific juniperoid nodules on the inclined tangential walls of ray cells in radial view, details not observed in our specimen. The described details of our specimen are included also in the more comprising diagnosis of Cupressinoxylon .

Excluding the similitude with Chamaecyparixylon by the absence of axial parenchyma, we consider a correct attribution of our specimen to the genus Thujoxylon , the correspondent fossil morphogenus for Thuja , 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). In time, numerous species of Thujoxylon were described (see also Vaudois & Privé, 1971 who revised the Cupressaceous fossil lignotaxa). Among the last described species we cite Thujoxylon antissum Süss & Velizelos, 1998 described from Lesvos, Greece, a Tertiary form representing a root wood with a special pattern of growth rings and cross section. The species was quoted and discussed again by Mantzouka et al. (2013). Some badly preserved specimens were described from Romani- an extra-Carpathian area as Cupressinoxylon sp. aff. Thujoxylon sp. ( Iamandei et al., 2008a; 2011; 2012). Also, a Cretaceous species named Thujoxylon beipiaoense Ding et al., 2016 was described from China. Also, taking into account the papers of Greguss (1967), Dupéron-Laudouéneix (1979), Zalewska (1953), the revised diagnoses of Kräusel (1949) and Vogellehner (1967; 1968), using the key of identification proposed by Vaudois & Privé (1971), and since our specimen has not sufficient details to support a specific identification we simply name it Thujoxylon sp.

Figures

Fig. 5 Thujoxylon sp. a, b - cross section: distinct growth-ring boundary, linear rays, very thick-walled tracheids in late-wood - x100-x200; c, d - tangential section: high uniseriate rays - x100; e, f - tangential section: rare small tangential pits on tracheids - x200; g, h - radial section: uniseriate spaced pitting - x200; i - radial section: cross-field pitting - x200.