Quercoxylon (Krausel) Gros, 1988

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 : 64-70

Quercoxylon sarmaticum Starostin et Trelea, 1969

Fig. 13 , photos a-i.

Material

From two samples of dispersed petrified wood, the first collected from Prăvăleni area, the left side of BodiȘteanu brook toward Cremenea hill and the second from Ociu village, on Church brook, from Mid-Miocene volcano-sedimentary deposits (Late Badenian-Early Sarmatian). The centimetric sized samples represent silicified wood fragments of beige color with whitish patches or gray, and are kept now in GIR collection at National Geological Museum - Bucharest under the inventory numbers 26381 and 26408 (field numbers: 79 and 282 respectively). Under the magnifying glass fibrous structure, annual rings distinct with visible large vessels and thick rays are visible, suggesting a dicotyledonate wood.

Microscopic description

The growth rings are distinct, the boundary is marked by the debut of the early wood with very large vessels, solitary or in small radial multiples, which reach in the late wood to very small size that they can be confused with fundamental elements, and usually appearing as irregular groups. The structure of the wood is ring-porous, the transition from the large vessels to the narrow ones of the transitional wood is abrupt. In a specimen (no. 79) a branch trace that locally disturbs the structure can be seen.

The vessels in the cross sections appear usually solitary, or in small multiples of 2(3) big vessels in the early wood, and solitary or radial multiples of 2-3 in the late wood or as irregular groups, sometimes with tangential development, of 2-5 or more small vessels mixed with vascular tracheids. The large solitary pores of the early wood are oval, sometimes deformed and radially elongat- ed, rarely circular. The smaller vessels of late wood are fairly uniform in size and are usually polygonal or slightly rounded to oval. Locally aspects suggesting a gradual decrease of the size of the vessels can be observed, but, globally appreciated, the structure has a typical ring-porous character. The vessel's walls are moderately thick, having 3-5 μm double wall. The lumen of the solitary pores has radial / tangential diameters (80)120-280(335) / (60)90-170 μm (even lower in the specimen 79, probably representing a branch fragment), and the late wood vessels have 35-64 / (20)32-64 µm. The vessel density is very variable in the early woods, there are interradial fascicles devoid of large vessels, but in the late wood, the vessel frequency is higher. In the longitudinal sections it is evident that the vessels have simple perforations on relatively inclined plates and intervascular bordered pitting, pits of 3-3.5 / 3.5-4 μm diameters, opposite, subopposite to alternate, numerous and relatively spaced, and with horizontal elliptical apertures of 1-2 μm. The pits to the ray cells are similar. The length of the vascular elements, difficult to measure, seems to be variable, of 80- 450 μm. Inside the vessels tyloses with recrystallised silica can be seen, and sometimes a dark content.

The vascular tracheids are very common, having similar pitting to the intervascular one, with pits rounded, or horizontal elliptic, spaced arranged in 1-3 vertical rows, with a diameter of 4-5 μm and large apertures of 3.5-4 μm.

The axial parenchyma - in cross section appear diffuse of apotracheal type, often difficult to observe, mixed between vascular tracheids, together constituting thick bands in early wood, but thinner, 1-2 seriate in the late wood. The parenchyma cells have of 16-20 μm in diameters, and generally have a dark content. Sometimes some parenchyma cells touch the vessels. In the longitudinal sections the parenchyma appear in strands of over 8 rectangular vertical cells with small, simple pitted, usually chambered and with large solitary crystals or small crystals and gum remains.

The medullary rays - in cross section seen have a wavy trajectory and are clearly two-sized. In tangential view they are either slender, numerous, 1(2-4)-seriate and of 6- 16 cells tall. The ray-cells are rounded to oval, of 8-16 μm in diameter. The multiseriate rays have 7-17 or more cells thickness (i.e. 80-380 μm) and are higher than 1 mm, vertically counting 94-115 or more rounded or polygonally shaped cells, relatively uneven in size (9.5-13- 20 / 12-20 μm) and with relatively not too thin walls (3- 5μm double wall). The frequency is 4-10 rays per tangential mm, the multiseriate rays are compact or composite, are rare and at relatively uniform distances in structure. In radial view the rays are homocellular, with cells all procumbent. In the cross fields with vessels numerous small bordered pits of 2-4 μm, spaced, sometimes indistinctly bordered or simple, rounded or oval, in 1-2 horizontal rows arranged, usually badly preserved. The ray cells are frequently crystalliferous and sometimes the crystals are slightly rounded.

The fibers - have a polygonal cross section with a fairly wide lumen of 8-13 μm in diameter and are moderately thick walled, of 4-5 μm double wall. Vertically are unsepted and unpitted.

Affinities and discussions

The appearance of the cross sections of the studied specimens is somewhat typical for the Fagaceae family in general (the wood with the ring-porous structure), and the presence of two sized rays, multi-seriate rays and numerous slender rays, especially uniseriate, and the aspects and the arrangement of the large vessels in the early wood and of the small vessels of the late wood are typical of quercineous taxa, especially for the genus Quercus L.

Shimanji (1962) made a comparative synthesis ( Table 3) of the essential xylotomic characters of the extant fagaceous taxa, based on the anatomical studies on phylogenetic relationships between the genera Fagaceae (in Suzuki & Ohba, 1991):

According to Hadziev & Mädel (1962) xylotomically there are four types of oak wood:

- Type "White oak" (Weisseichen) - the majority of the species of Lepidobalanus Endl. sectio, having ring-porous structure, polygonal vessels in the late wood, small and thin-walled;

- Type "Red oak" (Roteichen) - the species of Eritrobalanus Schwarz sectio and some species of Lepidobalanoideae - with ring-porous structure, round latewood vessels, large and thick-walled;

- Type "evergreen oak" - species of Quercus and Lithocarpus with diffuse-porous or semi-ring-porous structure, relatively small and rare vessels, most often radially arranged;

- Type "root wood oak" - corresponding to all the other wood types having diffuse-porous structure, with crowd- ed large pores.

In the same idea, Privé (1975) stated: the oak wood is characterized by vessels arranged in radial rows, more or less anastomosed (i.e. dendritic distribution), having simple perforations, two-sized rays, very thick, multiseriate, and slender, uni- or biseriate, such as in Quercus L. and Lithocarpus Bl. (= Pasania Oerst. ), fagaceous taxa represented by several dozen species in the temperate and warm regions of the northern hemisphere and islander also. The diffuse pore distribution characterizes at the both genera - the evergreen species; the ring-porous arrangement characterizes the Quercus deciduous species and most of the species of Lithocarpus from northern hemisphere. In root wood, the deciduous species often tend to lose their ring-porous arrangement, becoming similar to the evergreen species, and the thick rays are sometimes divided into false rays, i.e. aggregate rays (Privé, 1975).

Thus, there are useful observations for the identification of the wood structures of fossil Fagaceae that can be systematized (after Petrescu, 1976 - with modification, since Lithocarpoxylon was invalidated by Selmeier, 1997) as it follows:

I. Structures with solitary vessels and grouped (2-3 or more), fine rays (or 1-3 seriate) and multiseriate compact and with simple and scalariform perforations ( Fagus, Nothofagus - Fagoxylon, Nothofagoxylon );

II. Structures with solitary vessels, with simple perforations (sometimes scalariform, with few bars):

- Castanoxylon ;

- Rays uniseriate and multiseriate compact (sometimes compact-composed or parti

Quercoxylon of deciduous type;

-

Quercoxylon of evergreen type as equivalent of the extant Quercus of evergreen type and of Lithocarpus .

Studies on the fossil oak wood remains are numerous, and we cite only what we have consulted: Müller-Stoll & Mädel (1957); Brett (1960); Gottwald (1966); Greguss (1969); Nagy & Petrescu (1969); Kramer (1974); Hadziev & Mädel (1962); Petrescu (1969a,b,c;, 1976; 1978); Petrescu & Dragastan (1971); Petrescu & Liszkay (1974); Petrescu & Nuțu (1981); Starostin & Trelea (1969; 1984); Lupu (1984); Privé (1975); Privé & Brousse (1976); Gros (1983; 1988); Privé-Gill (1984; 1990); Samuel (in Lamouille et al., 1985); Selmeier (1958; 1971;1992; 1997); Suzuki & Ohba, (1991).

The fossil genus Quercoxylon was created by Hofmann (1929), but defined by Kräusel (1939) and emended by Müller-Stoll & Mädel (1957) and then by Gros (1983; 1988). Some authors consider Kräusel (1939) the author of the genre (see Selmeier, 1997). We could not consult the work published by Elise Hofmann (1929, in Ann. Sabariensis, 3: 81-87, plates 1-4) as is quoted by Müller-Stoll & Mädel (1957), by Greguss (1969), by Privé-Gill (1984; 1990) or by Suzuki & Ohba (1991), but because that first author has not designated a type-species and did not give a generic diagnosis, the genus name proposed was considered nomen nudum. Until to be established and broadly accepted genus name Quercoxylon , authors such as Goeppert, Felix, Unger, Conwentz, Mercklin, Schleiden, Edwards, Schuster, Platen, Knowlton, Pampaloni, Webber, Nee, Ogura, Watari, Shimakura used for fossil wood of Quercus type, names such as Kloedenia , Quercinium, Quercites or Quercus (see Müller-Stoll & Mädel, 1957).

The generic diagnosis for Quercinium was given by Unger (1842), and reviewed by Felix (1884). The diagnosis of the genus Quercoxylon was established by Kräusel (1939), having as a type species Q. retzianum Kräusel, 1939 , not mentioning that Hofmann (1929) has described the species Q. cerris , even without defining the newly created genus. However, the description of these species, reconsidered as a typical species, could have replaced the generic diagnosis. Anyway, denying Hofmann work and perhaps not knowing Kräusel's work from 1939, Andreánszky (1952) makes a new definition of the genus Quercoxylon , having the type Q. avasense Andreánszky 1952 .

Anyway, the correct generic diagnosis given by Kräusel (1939) was reviewed by Müller-Stoll & Mädel (1957) and is the following: Secondary wood with a porous or annular structure, with more or less obvious growth rings, usually with solitary vessels with simple perforations, large, alternate vascular pitting, increased to the parenchyma or to the ray cells, irregularly oval to polygonal, usually vertical, the ground tissue comprises libriform fibers, tracheids and vessels, parenchyma variably arranged, diffuse or in short tangential uniseriate bands, rays two-sized, the uniseriates not too tall, sometimes forming false rays.

The genus is however emended once again by Gros (1983, 1988), who confirm the correct fossil genus name as Quercoxylon . Ignoring this work, a new revision is made by Suzuki & Ohba (1991), who, describing a new species proposed to get out from confusion of all the quercineous generic fossil names. But they admit, and even emend, the genus Lithocarpoxylon Petrescu, 1978 later invalidated by Selmeier (1997). They also created new combinations by reviewing Quercoxylon species, coming back to the linnéan name of Quercus L., proposing the synonymy of Kloedenia , Quercinium, Quercites and Quercoxylon genera. Their proposal was not consistent with the ICBN recommendations, and was not taken into account by the scientific community. Of course, the use of the subgeneric taxonomic categories as is suggested by the authors may be interesting, but the proposal to return to the generic botanical name of fossil wood taxa was not followed by paleoxylologists in papers published after this "revision", which used only the name Quercoxylon (see Selmeier, 1997). The analysis of the characters presented by the here studied specimens shows their belonging to the Quercus - type white-oak ("Weisseichen"), of the Lepidobalanus section, because they present in the cross section the ring-porous structure and the vessels in the late wood are small, polygonal, thin-walled, and their distribution seems to be very diverse, as was observed also by previous authors, especially by Selmeier (1971) and Privé (1975). The combination of characters observed in the studied specimens, send to Quercoxylon bavaricum Selmeier, 1971 , a species where the author also observed a rather big variation in the vessels distribution in the late wood, separating even five types aspects found also by Privé (1975):

- Net dendritic arrangement, as radial complexes separat- ed by fiber rows;

- Diffuse arrangement;

- Few or absent vessels, of any arrangement;

- Late wood vessels separated by a fibrous area of the early wood;

- Gradual decrease of vessels' size arranged in radial complexes separated by fibers.

The different types of distribution of the vessels in the late wood can correspond to some environmental variations that have affected the growth of the trunk. The final (latest) wood well-developed wood indicates an irrigated soil, when a dry climate is manifested by the reduction of the final wood. In addition, the location of the sample in the tree can influence the different proportions of final wood, which appears to be larger at the base of the trunk, than just below the crown and to the trunk periphery. Also, the growth rings in the branches are smaller than those in the trunk. Privé (1975, p. 125), continues showing that the review of the species of "white oak" described shows that the divergences found from one species to another often represent intraspecific variations also observed in the extant oaks. However, as the Quercus genus shows a great interspecific anatomical homogeneity, we cannot determine the basis on which we can draw the boundary between the fossil species, so that they often have only a descriptive value.

Selmeier (1997) observes that the diameter of the vessels, the thickness of the rays, their frequency as well as their arrangement are variable, and even in the same species of fossil wood species different numerical values can be found. For this reason in the anatomical descriptions and in the current tree or shrub identification papers, no updated measurements are available. As a result, accurate measurements made with the usual paleoxylotomic descriptions are not always very useful in the identification process. The more, we believe that the normative indications contained in the " IAWA List of Microscopic Features for Hardwood" (Wheeler et al., 1989) require some method differences, to the expression mode of older measurements. Even in these conditions, comparing the structure highlighted by our specimens, with those already described, we believe that it is not wrong to attribute them to a genre that seems to have dominated the European Tertiary. However similar forms, even identical (see Petrescu, 1976), were described in the Pannonian space by Felix (1884), Andreanszky (1952), Hofmann (1929), Greguss (1969), Müller-Stoll & Mädel (1957). Also from the Carpatho-Balcanian region by Starostin & Trelea (1969), Lupu (1984), Nagy & Petrescu (1969), Petrescu (1969a,b,c; 1976; 1978), Petrescu & Dragastan (1971), Petrescu & Liszkay (1974), Petrescu & Nuțu (1981), Iamandei & Iamandei (2011a, b), Iamandei, E. et al. (2001; 2011), Iamandei et al. (2008b; 2012; 2013; 2014; 2016; 2017) some of them already cited upward.

In the spirit of ICBN Rules, we believe, as Petrescu (1976) did, that the species Quercoxylon bavaricum Selmeier, 1971 and Q. sarmaticum Starostin et Trelea, 1969 are identical, and we think that the species described in Romania, published by Starostin et Trelea (1969) with two years ago that the species of Selmeier (1971) has priority, so that the specimens described here will bear the name Quercoxylon sarmaticum Starostin et Trelea, 1969 . This type of oak corresponds most likely to the species Quercus robur L., a species present in the extant Romanian flora.

Figures

Fig. 13 Quercoxylon sarmaticum Starostin et Trelea, 1969. a, b - cross section: semi-ring-porous wood, two sized rays, ray dilation at the growth-ring boundary - x100; c - cross-section: usually solitary vessels, thick to very thick walled fibres - x200; d, e, f - tangential section: broad fusiform rays, high, dissected - x100; g, h, i - radial section: simple perforations (g, i), alternate pitting on vessels and on vascular tracheids pitted parenchyma (g, i), bad preserved cross-field (h, i) - x200.