Fagoxylon subcaucasicum Privé et Brousse, 1969

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 : 58-62

Fagoxylon subcaucasicum Privé et Brousse, 1969

Fig. 11 , photos a-i

Material

From nine samples of dispersed petrified wood collected from Prăvăleni area, at the confluence BodiȘteanu brook, from the cliffs of the base of Cremenea hill from Mid-Miocene volcano-sedimentary deposits (Late Badenian-Early Sarmatian). The samples represent quite friable silicified wood fragments of dark to black color and centimetric sizes, and are kept now in GIR collection at National Geological Museum - Bucharest under the inventory numbers 26,365; 26,366; 26,368; 26,471; 26,282; 26,371; 26,372; 26,376 and 26,378 (field numbers: 30; 31; 34; 42; 43; 44; 45; 55 and 59 respectively). Under the magnifying glass fibrous structure, annual rings distinct and thick rays appear, suggesting a dicotyledonate wood.

Microscopic description

The growth rings - are distinct, with boundary marked by thicker walled and flattened fibers. The early wood begins abruptly, with large vessels, the wood is diffuse-porous to semi-ring-porous, the diameter of the vessels gradually decreasing to the late wood. In the early wood predominate the groups generally radially oriented and in the late to final wood there are small, solitary pores. The rays show obvious "platanoid" dilations at the annual ring boundary. The histological elements seem to be obviously affected by the tafonomic processes, in which a probable initial wood charring is assumed, followed by silicification.

The vessels in the cross section are presented as solitary pores with oval-rounded or angular-rounded contour or star like, or in radial multiples of 2-5(8), or in irregular quasi-radial groups of 4-5(11) vessels, especially in early wood. In the late wood the vessels are slightly smaller, gradually decreasing and usually solitary, and the end zone of the growth ring is marked by fibers or parenchyma which seem to be arranged as terminal bands, the vessels being very small and rare or missing. The radial / tangential diameter of the vessel lumen is (13)25-60(84) / (8)20-58(76) µm. The density is quite variable, of 100-

284 pores per mm2, the vascular walls do not look too thick, they have a 4-6(8) µm double wall. Vertically, round to elliptical perforation can be seen but also scalariform, inclined, low, with 7-10-15 relatively thin bars sometimes bifurcated, and with numerous round to oval finely bordered pits, obviously passing to scalariform pits. They have circular or horizontal oval apertures to the horizontally elongated in the scalariform ones, having diameters of 3-5 / (5)8-13 up to 17-24 µm. Sometimes appear, intercalated among the horizontal scalariform pits, vertical elongated or triangular pits with relatively large apertures, breaking the order. The vessel lumina may exhibit yellow or black solid debris an also large tyloses moderately thick-walled (3-4 μm double walls) and slightly emaciated. Some vessels have isolated or grouped crystals. The length of the vascular elements is (160) 280-500 μm. In some cases, weak spiral thickenings can be seen.

The axial parenchyma is usually difficult to observe in cross sections, although it is present in longitudinal view as vertical strands of chambered cells with large solitary crystals. Frequently, strands of parenchyma cells devoid of crystals also appear.

The medullary rays - in cross section appear to be of two sizes: some finer, 1-5-seriate and some multiseriate, of 10-15 cells wide, usually with dark content in their cells. The rays have a relatively straight or slightly curved trajectory and show obvious dilation at the boundary of the growth rings. Sometimes, disjunctive aspect appear as tangential fissures of the thick rays, and is difficult to say if they are a consequence of fossilization processes or are formed during the life of the tree, although tubular processes between cells that kept alive the organ can be detected. Generally, however, the cellular structure of the rays in most of the studied samples, in particular those charred and silicified, is disorganized. In tangential view the multiseriate rays are thick (of 84-135 μm), and over 1 mm high. In the ray body, often large cells, either dark or bright-white colored, sometimes having polygonal or rounded crystals, locally outline the thick rays as incomplete cell-sheath. The thinner rays are usually low, but can have up to 30 cells in height. Ray frequency is 4-8 rays per horizontal tangential mm. Radially with tendency to heterocellular, the rays have up to 4 rows of marginal procumbent to square cells occur, slightly higher than the regular ones, rarely tall cells, of 17-22 μm. The body ray-cells are moderately thick walled and are usually narrow, procumbent, and of 8-16 μm tall in the multiseriate rays, but sometimes mixed with square cells empty or with solitary crystals or small crystals or sand of crystals, transparent, floating in a dark content. Some other cells have only yellow-orange content. The uniseriate rays have taller cells, of 18-24 μm. So, we can speak of weak tendency of heterogeneity in the ray architecture, which is however relatively homogeneous. The cross fields have small, opposite, round to oval bordered pits or elongated to scalariform, especially in the marginal fields, with diameters of 3.5-5/5-10 μm, arranged on (1)2(3) horizontal rows.

The fibers are sometimes difficult to observe when the structure is crushed among numerous vessels, especially in early wood, but occurs in large quantities to late wood, where the vessels are smaller, rare, or even missing. The fibers have a polygonal cross section, usually rectangular, relatively large lumina and thick walls. In the longitudinal sections are usually difficult to observe, because they are crushed and sometimes have a black, compact content, horizontal cracks, difficult to interpret them as parenchyma or fibers.

Affinities and discussion

The semi-ring-porous wood, the aspect and size of vessels in cross-section, the intervascular bordered opposite pitting with pits oval-elongated to scalariform, the vessels with simple and scalariform perforations and the presence of two sized rays with dilations at the ring boundary, are good xylotomic arguments to consider that the studied sample might come from a member of the Fagaceae family (in Watson & Dallwitz, 1992). Among the current fagaceous taxa, most affinities were found to be with the genus Fagus , the species F. sylvatica L. and F. orientalis Lipsky whose current living area comprises western and central Europe respectively meridional-oriental Europe, Turkey, Caucasus and Iran area (see Metcalfe & Chalk, 1950; Greguss, 1959; Privé-Gill & Watelet, 1980; Schweingruber, 1990).

The correspondent fossil genus Fagoxylon was established by Stopes & Fujii (1911), revised Süss (1986), having F. hokkaidense (Stopes & Fujii) Süss, 1986 as type species and has the next diagnosis: Wood structure with wide growth rings, with clearly defined early and late wood, less obvious in root wood, usually with solitary vessels and in radial short multiples or otherwise grouped, regularly distributed within the growth ring, with a mean radial / tangential diameters of 50-90 / 35-60 μm (smaller in branches, of 30-40 / 20-25 μm), density is 70-300 vessels per mm 2 (for branches - up to 600). Spiral thickenings on the ends of the vessels often appear, simple perforations and scalariform with 1-30 bars, intervascular pitting opposite to scalariform, pitted fibers, irregularly arranged or radial rows (in roots and branches appear fewer). Diffuse apotracheal parenchyma, in short uniseriate bands and few paratracheal. Two sized rays either very tall and thick, of 20 or more cells wide (in roots and branches there are no more than 15), but also thinner, of 1-7 cell in thickness, with dilation at the boundary of growth ring, homogeneous to slightly heterogeneous, ray cells of 12-20 μm average diameter, with half-bordered pitting to vessels usually horizontally elongated to scalariform, opposite or irregular. Idioblasts with crystals sometimes present in rays.

Süss (1986) made a revision of the species of Fagoxylon previously described and described two new species, the list of the valid species is the following:

- Fagoxylon acerinum (Windisch) Süss, 1986 ;

- F. caucasicum (Felix) Süss, 1986 ;

- F. subcaucasicum Privé et Brousse, 1969 ; Privé-Gill & Watelet, 1980;

- F. crystallophorum van der Burgh, 1973 ;

- F. francofurtense (Mädler) Süss et Müller-Stoll, 1984 ;

- F. grandiporosum (Beyer) Süss, 1986 ;

- F. hokkaidense (Stopes & Fujii) Süss, 1986 ;

- F. hondoense (Watari) Süss, 1986 ;

- F. kraeuselii Hofmann (see Hofmann, 1952);

- F. mikofalvense Süss, 1986 ;

- F. radiatum Süss, 1986 . Generically are also considered to be well attributed some other specimens studied by Slijper, Shimakura and Andreanszky (Süss, 1986), but many species of Fegonium (or Phegonium ) described by various authors (see again Süss, 1986) and also Fagoxylon australe Salard, 1961 - are not considered valid. In fact, the confusion was based on the fact that Plataninium Unger, 1842 was a too comprehensive taxon according to the diagnosis emended by Page (1968), who included fossil wood specimens from Fagaceae ( Fagus ), Platanaceae ( Platanus ), Eupteleaceae ( Euptelea ) and Icacinaceae ( Citronella, Ottoschultzia ), whose family relationships can not be definitely determined, but which have similar xylotomic characters (see Süss & Müller-Stoll, 1977 and Selmeier, 1996). Of these, Plataninium aceroides (Goeppert) Windisch, 1886 and Plataninium sp. (in Edwards, 1931) became Fagoxylon acerinum (Windisch) Süss 1986 , and other valid species remained nomen ambiguum until a revision of the original material. In the spirit of the principles and rules of botanical nomenclature ( ICBN, 1999) we believe that the invalidation of the name Plataninium proposed by Süss & Müller-Stoll (1977) must remain valid.

The characters taken into account by Süss (1986) in identifying Fagoxylon species are the following: the distribution of vessels and fibers in the cross section, the variation in size of the vessels within the growth ring and the height of the ray cells. Using the model of the cited author, we have completed the data of the material studied by us, in the Table 2:

From this table it is obvious that the specified species slightly differ of our studied material regarding the ray-cells size, the disposition of the vessels in the growth ring, and the comparison of all the described aspects of these species do not conform to those presented by the material studied by us here.

However, there is a similarity up to the identity of the figurative aspects described in our specimens with those described by Privé & Brousse (1969) from Bastide-du-Fau, found again at the same level, at Aubart (Cantal Massif), from late Miocen (Privé-Gill & Watelet, 1980). This similarity suggested us to attribute the here studied material to the species Fagoxylon subcaucasicum Privé et Brousse, 1969 , initially considered a fossil correspondent of the extant European Fagus sylvatica L. even if xylotomically this fossil species has a structure mostly similar to F. orientalis Lipsky (Privé-Gill & Watelet, 1980) , both living yet today in the Romania.

The comparative approach, in order to identify the correct taxonomy of the studied material, forced us to reconsider the determination of sample 43 (Inv. No. 26,282) which was originally published as Platanoxylon bohemicum Prakash, Březinová et Bůžek, 1971 (see Iamandei & Iamandei, 1997). In fact, Süss & Müller-Stoll (1977, p. 57) have invalidated this species, considering that it does not have the characters of a plane wood. The xylotomic characters of the specimens studied here are almost identical, including those of specimen 43, all representing Fagoxylon subcaucasicum Privé et Brousse, 1969 .

Figures

Fig. 11 Fagoxylon subcaucasicum Privé et Brousse, 1969. a, b - cross section: difuse-porous wood, two sized rays, ray dilation at ring boundary - x50; Photo c - cross-section: distinct ring boundary, diffuse porous structure - x100; d, e - tangential section: broad fusiform rays, vessels - x100; f - tangential section: badly preserved pitting - oval horizontal opposite pits to scalariform - x200; g, h - radial section: simple perforation, and scalariform piting on vessels - x200; i - radial section: scalariform cross fields with vessels - x200.