Laurinoxylon aff. czechense Prakash, Březinová et Bůžek, 1971

Laurinoxylon aff. czechense Prakash, Březinová et Bůžek, 1971

Fig. 2 View Fig , photos a-I

Studied material. From the studied material, 12 samples showing similar lauraceous structure were selected as Laurinoxylon - Type 1 – ( Mantzouka et al., 2016), representing fragments of silicified wood, collected from lower Miocene volcano-sedimentary deposits of Lesvos, numbered with Lsv59, Lsv63, Lsv65, Lsv71, Lsv116, Lsv374, Lsv385, Lsv386, Lsv387, Lsv388, Lsv393, Lsv395. These samples are registered and kept in the Collections of the Faculty Geol. & Geoenviron. of NKUA .

Microscopic description. The growth rings – are distinct in cross-section, usually showing a difuse porous wood structure, with relatively distinct ring boundaries, marked by some rows of smaller fibres, abruptly followed by the early-wood with normal sized fibres and with larger vessels.

The vessels – in cross-section viewed, appear usually thick-walled, mainly solitary and in small clusters or small radial multiples or of 2-3, in radial patern between two successive rays, defining a diffuse porous arrangement. However, sometimes, in the final wood the vessels appear slightly smaller, suggesting a tendency to a semi-ring-porous arrangement. The solitary vessels are round to oval and have the radial / tangential diameter of 50-110(-150) / 40-85(-120) µm. When grouped, the vessels are slightly deformed by compression. Their walls are relatively thick, of 7-10 µm the double wall. In the late-wood the vessels could be slightly smaller than 50 / 40 µm r / tg.d. In the longitudinal view, the perforation plates appear of simple type, more or less inclined. The intervessel pits have an alternate arrangement, and are polygonal and medium-sized, with a diameter of around 10 µm. The vessel-ray pits are quite similar to intervessel pits, in size and shape: the cross-field pitting is described below. Helical thickenings in the vessel elements are not present. The mean tangential diameter of vessel lumina is around 65 µm. Vessel density is of 52–74 vessels per square millimeter (mean density 63). Mean vessel element length is around 550 µm (between 350 - 800 or more). Tyloses in vessels commonly appear. Deposits in vessels usually not present.

Tracheids, vascular fibres or vasicentric tracheids – not observed.

The fibres – constitute the major part of the ground tissue, and are sometimes septate and usually not pitted, or difficult to observe, due to poor preservation.

The axial parenchyma – appears relatively few, as scanty paratracheal and of vasicentric type, around the solitary or grouped vessels. On the vertical walls 1-2-seriate simple pits appear. The end-walls are horizontal to slightly inclined.

The rays – are 1-3 seriate, but commonly 2-3 seriate. Their height, in tangential sections, appear low to high, of 3 up to 25 cells, (up to 300-500 µm) with the terminal cells triangular, or flame-like. Radially, appear a heterocellular aspect, with body ray-cells all procumbent and with 1-2 rows of marginal cells taller, square and/or upright (of 4-12 µm), some of them as hypertrophied idioblasts, globular to oval shaped or flame-like, usually having dark or bright content. The cross-fields with vessels show some round pits, of 5-7 µm in diameter, in horizontal row arranged. Sometimes larger pits on the taller marginal fields can be observed. Sheath cells and tile cells are not present. Ray density - up to 12 rays/mm tangential.

Storied structures – not present, neither to rays nor to the axial parenchyma and/or vessel elements. Secretory elements – appear as oil and/or mucilage hypertrophied ray cells, as idioblasts associated with rays, as described above. Intercellular canals – as normal or traumatic axial or radial canals not observed. Cambial variants and included phloem absent. Mineral inclusions not observed. Affinities and discussions. From the here studied samples of petrified wood with dicotyledonous structure, 12 samples collected from Lesbos island, quoted above, showed a similar lauraceous structure, essentially characterized by the presence of typical flame-like idioblasts associated with rays. They usually show a diffuse porous structure, with vessels mainly solitary and in short radial multiples, thick-walled, with simple perforations, and alternate intervessel pits, with parenchyma few scanty paratracheal to vasicentric, with rays 1-3 seriate, heterocellular, having 1-2 marginal rows of taller or upright cells, often hypertrophied, oval or flame-like, and full of oil and/or mucilage, representing those specific idioblasts.

All these xylotomic details observed in the studied fossil specimens, but especially the presence of the typical idioblasts suggest a possible affinity with the Lauraceous taxa, as it appears specified in the papers of Metcalfe & Chalk (1950), Greguss (1954, 1959), Schweingrüber (1990), Watson & Dallwitz (1992), Schoch et al. (2004), Wheeler (2011), Akkemik & Yaman (2012) and Mantzouka et al. (2016).

Lauraceae is a rich plant family, having about 45 current genera with around 2850 species, which are spread mainly in the warm regions: tropical America, Brazil, Southeast Asia, Australia, and the Pacific islands. Laurus is the only genus living in Europe, with few species, appearing in the Mediterranean region and in southern Europe and warm temperate Asia, including Northern Africa and the Middle East ( Laurus - Wikipedia, accessed 05.09.2023).

Considering the location of the mucilaginous idioblasts as a main taxonomic indicator, Mantzouka et al. (2016) showed that there are 4 types of Laurinoxylon , as it follows:

• Laurinoxylon Type 1 – with idioblasts associated only with ray parenchyma cells, +/- crystals;

• Laurinoxylon Type 2a – with idioblasts associated with both ray and axial parenchyma, +/- crystals;

• Laurinoxylon Type 2b – with idioblasts associated both with rays, also present among the fibres, + crystals (more or less numerous);

• Laurinoxylon Type 3 – with idioblasts associated with ray and axial parenchyma and also among the fibres, +/- crystals).

Thus, Berger (1953b) described the species L. weylandi from around Wien ( Austria) as having one row of upright and/or square marginal ray cells, so a Laurinoxylon of Type 1, fairly similar to here studied specimens. In other paper (see Berger 1953a), he described L. ehrendorferi Berger , from the Aegean area (from Limnos, Tessaloniki) as having frequently grouped vessels and oil and/or mucilage cells, associated with ray parenchyma but, Mantzouka et al. (2016) suspected the presence of idioblasts associated to parenchyma cells and considered this species as Laurinoxylon of Type 2a, similar to L. mueller-stollii Greguss, 1954 and to L. microtracheale Süss, 1956 (in Süss, 1958).

Schönfeld (1956) have described a L. parenchymatosum from Germany, which have one row of upright and / or square marginal ray cells (a Laurinoxylon of Type 1), and is characterized by the presence of more numerous axial parenchyma cells and, so, is quite similar to our studied specimens.

Also, from Germany, Süss (1958) has described a new species of Laurinoxylon Type 1, as L. litseoides Süss , presenting idioblasts, associated with rays. This species, L. litseoides Süss was also recently identified in Turkey (see Akkemik et al., 2019; Akkemik, 2021). Other new species of Süss (1958) identified as L. hasenbergense Süss and L. microtracheale Süss are Laurinoxylon of Type 2a, and a L. endiandroides Süss is a Laurinoxylon of Type 3, both proposed for revision, having some xylotomical details which does not agree with the diagnosis of Laurinoxylon (see Mantzouka et al., 2016, p.470).

Huard (1967) has described another Laurinoxylon of Type 1 from some Neogenes lignites from Arjuzans, France, as Laurinoxylon perfectum Huard , which is quite similar to our specimens.

Also, from Transylvania, Romania, Iamandei & Iamandei (1997) have described a Laurinoxylon of Type 1, as L. neagui Iamandei et Iamandei , also slightly similar to studied specimens in the present research.

Prakash et al. (1971) have described from Czech Rep. two species of Laurinoxylon of Type 1: as L. oligocenicum , found and described also by Petrescu (1978) from Romania, and as L. czechense , also of type 1, found and described later again by Sakala et al. (2010) from Czech Rep., both quite similar to our studied specimens. Another similar form of Laurinoxylon Type 1, was described by Mantzouka et al. (2016) from Lesbos, and named Laurinoxylon aff. czechense Prakash et al. , suspecting that the original species L. czechense Prakash et al. is quite similar to the current Cinnamomum camphora (L.) J. Presl., which is of Type 3.

Thus, in the here studied specimens we described: growth rings with quite distinct boundaries and with porous; vessels with tg.d.<100 mm, relatively thick-walled, solitary or grouped in small radial multiples of up to 2-3 vessels, vertically showing usually simple perforation plates; alternate intervessel pits mean-sized, with 4-10 µm; vessel-ray pitting, similar; mean density 63 vessels per sq.mm.; fibres usually not pitted and sometimes septate; axial parenchyma scanty paratracheal to vasicentric few; rays 1-3 seriate, but usually 2-3 seriate, low to high, of 3 to 25 cells or more, with terminal cells triangular, high, ovoid or flame-like; ray density around 12 rays/mm tg.; radially show heterocellular character, with cells all procumbent in the ray-body, and 1-2 rows of marginals cells taller, square or upright, some of them hypertrophied, as globular to oval, or flame-like, usually having dark content; cross-fields with some round pits medium-sized in horizontal row arranged.

All these features clearly indicate a Laurinoxylon Type 1 ( Mantzouka et al., 2016), and are very similar, up to identity with Laurinoxylon aff. czechense Prakash, Březinová et Bůžek, 1971 , to which we assign the studied specimens, and we consider it as a perfect ancestor of the current Laurus nobilis L., a species still living in the Mediterranean region.