Quercoxylon intermedium Petrescu & Velitzelos, 1981

Quercoxylon intermedium Petrescu & Velitzelos, 1981

Fig. 7 View Fig , photos a – i.

Studied material. Numerous petrified (silicified) wood remains (87 samples) showed a similar oak xylostructure. They were collected from late Oligocene deposits of Evros, more specific from Aetohory – 16 samples numbered with the field numbers: Aet238, Aet303, Aet304, Aet305, Aet317, Aet319, Aet322, Aet326, Aet327, Aet330, Aet332, Aet984, Aet985, Aet994, Aet1135, Aet1136); 11 samples from Fylacto with field numbers: Fy25, Fy157, Fy158, Fy159, Fy160, Fy161, Fy162, Fy163, Fy1137, Fy1138, Fy1139; 6 samples from Dadia, with field numbers: Dd710, Dd711, Dd712, Dd713, Dd714, Dd715; 10 samples from Likofi, with field numbers: Lkf239, Lkf 240, Lkf 241, Lkf 242, Lkf 243, Lkf 244, Lkf 245, Lkf 246, Lkf 247, Lkf 248; 23 samples from Provatonas, with field numbers: EP1 D1, EP2 D4, EP3 D4, EP7 D5, EP8 D6, EP11 D7, EP13 A D8, EP13 D9, EP14 D10, EP15 A D11, EP15 D12, EP17 D13, EP19 D15, EP20 D22, EP20 A D16, EP27 D17, EP34 D18, EP35 D19, EP40 D20, EP1999 D21); 9 samples from Lefkimi, with field numbers: Lfk267, Lfk276, Lfk278, Lfk280, Lfk285, Lfk287, Lfk289, Lfk324, Lfk328a; one from Sappes – field number: Spp1084; and two from Chalkidiki – field numbers: Ckdk439 and Ckdk440. Also, 4 samples from Limnos island, with field numbers: Li78, Li224, Li225, Li482; and 5 samples from Lesvos island, with field numbers: Lsv7, Lsv82, Lsv407, Lsv410, Lsv546. They are all registered under these field numbers and kept in the Collections of the Faculty of Geol. & Geoenviron., of NKUA.

Microscopic description. The growth rings – are present in the secondary wood, but with less distinct ringboundaries, that difficultly can be guessed there where, after the late-wood with small vessels, and some final rows of ground tissue devoid of vessels are suddenly followed by the early-wood with normal sized fibres and large vessels. Also, the presence of two-sized rays gives to the structure a typical aspect. In some studied specimens the structure is crushed or poorly preserved, so fewer well-preserved xylotomical details can be recognized, but the general aspect of the structure is typical.

The vessels – appear, in cross section, almost exclusively solitary, rarely in pairs or small groups and their arrangement define a wood structure of semi-ring porous type, with larger solitary vessels in the early-wood, gradually diminishing to the late-wood. Sometimes, a tendency to porous or even ring porous aspect appears, possibly as intraspecific or climatic variability. The large solitary vessels have the lumina size of 100-260(-290) / 100-220 μm the radial / tangential diameter, gradually diminishing to 60-90 / 50-90 μm in the late- wood. The shape of the solitary pores is usually round to radial oval and have thick walls, of 5-8 μm the simple wall. Vessels' arrangement is very specific due to the presence two-sized rays, i.e. between two thick rays there appear a composite general bundle with radial pattern and/or diagonal, sometimes even with dendritic aspect. It comprises all the vessels which, between two successive thin rays, are radially arranged. Often, between two thin rays, few vessels appear or not at all, but all together contribute to that diagonal or dendritic aspect of the structure. However, in some specimens, between two uniseriate rays appear radial rows of vessels of almost similar size (in many specimens from Provatonas area). In other bundles some irregularities can appear, but usually, all these bundles show obvious gradual diminishing vessels' size to the late-wood, which gives the typical semi-ring-porous aspect of the structure. In longitudinal view, the vessels show exclusively simple perforation plates, sometimes less visible, because the presence of tyloses or of bad preservation. On the vertical walls, numerous, round intervessel pits appear, or toward the vasicentric tracheids, having opposite, subopposite to alternate arrangement, contiguous or spaced. These pits of bordered type are mean sized, of 5-10 µm in diameter. The vessel-ray pits are quite similar to the vascular pits, in size and shape, having much reduced borders, to apparently simple, corresponding to the cross-field pitting, which is described below. Helical thickenings in vessel elements were not observed. The tangential diameter of vessel lumina varies between 50-220 µm and the mean tangential diameter is around 100 µm. Vessels' density is of 5-20 vessels/mm 2. The mean vessel element length is around 350 µm or slightly more. Inside the vessels' lumina, visible in all sections, more or less numerous and relatively thick-walled, big and/or small tyloses commonly can be seen. Also, sometimes appears in vessels or inside tyloses, fungi as hyphae, or some tanninous dark content.

Vasicentric tracheids – are present, surrounding the vessels, having pitted vertical walls with 1-2(3)-seriate, bordered pits of 4-5 µm in diameter.

The fibers – constitute the major part of the ground tissue, are relatively thick walled and, on the vertical walls have small bordered pits. Also, they are not visibly septate.

The axial parenchyma – constitute the major part of the ground tissue, are relatively thick walled and, on the vertical walls have small bordered pits. Also, they are not visibly septate.

The axial parenchyma – in cross section appears as few cells, dispersed between among the fibers, often difficult to identify each other, in cross-section, having quite similar aspects, but usually the parenchyma appears as narrow bands (1-3 cells wide), visible as tangential shorter or longer bands, even suggesting an almost reticulate arrangement. Sometimes those bands of parenchyma are slightly irregular as direction or thickness. In longitudinal view, the parenchyma can be recognized as rows of vertical-rectangular cells, often chambered and crystalliferous, usually with big or small rounded crystals inside, floating in a tanninous dark content, in which appear round empty spaces, like variably sized bubbles (especially in the samples from Licofi and from Lefkimi).

The rays – after their thickness are rays of two distinct sizes: thin rays, usually exclusively uniseriate, rarely 2-3- seriate (as in many specimens from Provatonas), which in cross-section appear as molding the vessels, and thick rays, multiseriate, commonly more than 10-seriate, of compact type or, mostly, of compound type, i.e. dissected by numerous libriform fibres, so giving typical aspect of almost aggregate rays, or are even of typical aggregate type, as it appear in almost all the studied specimens. Regarding the ray height in tangential view, the fine rays are usually low, but the multiseriate rays are high to very high, often more of 1 mm. Also, the ray cellular composition, observed in radial view, shows that the rays are in some cases homocellular, with all ray cells procumbent, but usually are heterocellular, having the body ray cells procumbent and 1-2(-3) marginal rows of taller cells, as square or even upright cells. In cross-fields with vessels, large quadrangular simple pits 8-12(-15) / 4- 5 µm, in palisade arrangement appear, sometimes with rounded corners or lens-like (of 15-20(25) / 5-6 µm), usually vertical, but sometimes tilted up to horizontal, but often poorly visible, because the ray cells are full of dark content and or rounded crystals or, simply, are poorly preserved. Between the horizontal ray cells, the tangential wall is relatively thick and is vertical to inclined. Ray density is between 4-12 rays/mm horizontal, sometimes more. Sheath cells or tile cells are not present.

Storied structures – absent. Secretory elements are absent. Intercellular canals – absent. Only in the sample Pvt8 appears, in cross-section, a traumatic rounded canal of big dimensions with lumen of 120/90 μm in diameters and with very thick walls, of 20-25 µm. It could be, also, an insect gallery, since is intersecting other structural elements. Cambial variants – as included phloem absent. Only in the sample Aet1135 appears a primary structure with pith and primary wood, suggesting a branch fragment. Mineral inclusions – are present as usually small, rounded crystals, in chambered axial parenchyma cells and in ray parenchyma cells. Also, is good to specify that in the specimens Pvt24 and Pvt35, clearly appear important deposits of suber.

Affinities and discussions. We had in study a big number or specimens (87) that showed a similar quercineous xylo-structure, characterized by wood semi-ring-porous, with almost exclusively solitary vessels, rarely in small groups, having simple perforations; with two-sized rays - the broad ones as compact-compound and/or aggregate rays and with typical cross-field pitting as quadrangular pits, „ in palisade “ arrangement. All these details are presented in a synthetic description of all the available specimens and strongly suggest a structure of Quercus type – Ilex Section, as it appears in the consulted papers of Greguss (1954), Hadziev & Mädel (1962), Schweingrüber (1990), Schoch et al. (2004), Wheeler et al. (2011).

Thus, in their study of some petrified oaks from Bulgaria, Hadziev & Mädel (1962) showed that the xylotomy of the current oaks corresponds to four structural wood types, as follows :

• „ Weisseichen“ – the white oak type, comprising most of the species included now in the section Quercus (see Denk et al., 2017), a group of species living now in Europe , Asia and North Africa, and characterized by a ring-porous structure, with small, polygonal and thin-walled vessels, in the late-wood .

• „Roteichen“ – the red oak type, comprising the species from Eritrobalanus section (now Lobatae section - see Denk et al., 2017), as well as some species of the Lepidobalanoideae (now Quercus section - see Denk et al., 2017), characterized by ring-porous structure, with relatively large, round, thick-walled late-wood vessels.

• The „evergreen oak“ type ( Ilex section), including species of Quercus and Lithocarpus , with diffuse-porous or semi-ring porous xylo-structure, the relatively small and spaced vessels, often being radially arranged.

• The „root wood“ oak- type, corresponds to all the oak types, showing diffuse-porous structure, and large and crowded pores.

Later, Privé-Gill (1975), noted in her studies that the oak wood is characterized by vessels in radial rows more or less dendritically distributed and showing only simple perforations. She emphasized, also, as a feature of taxonomic value, the presence of two-sized rays: multiseriate, very thick and, respectively, fine rays, uniseriate or biseriate, usually present in actual or fossil wood of Quercus and Lithocarpus . These genera have numerous species living in the temperate or warm regions of the northern hemisphere. The wood structure can also be diffuse-porous, typical of evergreen species, whereas the ring-porous structure is characteristic of deciduous Quercus species and the most northern Lithocarpus species. In the root-wood, the deciduous species often tend to lose their ring-porousness, becoming similar to the evergreen species, and the broad rays become divided into false rays, i.e. aggregate rays ( Privé-Gill, 1975). All these observations are in perfect accord with the observations of Hadziev & Mädel (1962).

A fossil species with very similar features was described from Evros, by Petrescu et Velitzelos (1981), as Quercoxylon intermedium , identified also by us in Rhodopes, Bulgaria (Iamandei et al., 2014) and, the xylotomy of the numerous specimens studied here is very similar, up to identity with the cited species.

Thus, comparing description of the studied specimens with the species diagnosis and based on the above discussion, we assign them to the fossil species Quercoxylon intermedium Petrescu et Velitzelos, 1981 , considering it as a fossil correspondent of Quercus ilex L. or, possibly, to Q. suber L., both native to SW-Europe, NW-Africa and Mediterranean basin (see Quercus ilex - Wikipedia - accessed 05.02.2023; Quercus suber - Wikipedia - accessed 05.02.2023).

Also, we consider that this type of oak had evergreen foliage, described from Aegean area as Eotrigonobalanus furcinervis (Roosm.) Walter et Kvacek, 1989 , (in Kvaček & Walther, 1989) and as is mentioned in other previous studies on fossil remains of oak, from Greece (see Selmeier & Velitzelos, 2000; Velitzelos et al., 1999; 2008).