Fagoxylon cristallophorum van der Burgh, 1973

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 : 62-64

Fagoxylon cristallophorum van der Burgh, 1973

Fig. 12 , photos a-i

Material

From eleven samples of dispersed petrified wood some of them collected from Prăvăleni area, the left side of BodiȘteanu brook from the cliffs of the base of Cremenea hill (field numbers: 36; 56; 71; 72) and from Ociu village area (104 and 599 on MarinaȘu valley; 239 in Ociu; 434; 444; 736 on Church brook and 675 on North Ociu brook) from Mid-Miocene volcano-sedimentary deposits (Late Badenian-Early Sarmatian).

The samples represent silicified wood fragments of gray to whitish color or beige to brown and of centimetric sizes, and are kept now in GIR collection at National Geological Museum - Bucharest under the inventory numbers 26,355; 26,377; 26,379; 26,380; 26,391; 26,404; 26,413; 26,414; 26,425; 26,432 and 26,445 (field numbers: 36; 56; 71; 72; 104; 239; 434; 444; 599; 675 and 736 respectively).

Under the magnifying glass fibrous structure, annual rings few distinct, vessels and thick rays can be seen, suggesting dicotiledonate wood.

Microscopic description

The growth rings are distinct, with the boundary marked by some rows of very thick-walled fibers, devoid of vessels. The early wood begins abruptly with large vessels, the wood is semi-ring-porous, the diameter of the vessels gradually decreasing to the late wood. In the early wood prevails the solitary pores. The rays show obvious "platanoid" dilations at the limit of the annual rings.

The vessels appears in cross section as solitary pores, prevailing in the early wood, with oval-rounded or angular-rounded contour to fairly star like, with corrugated walls, or in small radial or tangential multiples of 2-3(4) pores or as irregular groups, especially in early wood. To the late wood, the vessels are slightly smaller, gradually decreasing and are usually solitary, and to the final wood become smaller or are rare or missing. The radial / tangential lumina diameters of the vessels are of 24-65(125) / 20-60(90) μm. Their density is 100-140(184) pores per mm 2. The vascular walls are fairly thick, having 4-7 μm double wall (2.5-4 μm simple wall). The vessels have round to elliptical simple perforations but also scalariform, inclined, usually low, with 7-12(17) relatively thin bars, sometimes with rare bifurcations, and pitting numerous, opposed, rounded to oval with thin borders and evident tendency to scalariform. They have circular or oval apertures horizontally elongated to scalariform (3.5- 5 / 4-8 µm). The length of the vascular elements is 260- 330 μm. In some cases, weak spiral thickenings on the walls can be seen. The lumen of the vessels may show solid black granules or crystals, isolated or clustered, and sometimes large tyloses appear, visible even in cross sections.

Vascular tracheids are present, more visible in the longitudinal sections, close to the vessels, with large-round or elliptical-horizontal pits to scalariformes, on a single vertical row similar to those on the walls of the vessels.

The axial parenchyma - in cross section appear as obvious apotracheal, either diffuse as rare solitary cells among fibers, or as short tangential lines slightly waved, with polygonally-rounded cells or slightly deformed, larger than the very thick-walled fibers from around and have 11-15(18) µm in diameter. They appear also in the final wood and are visible in the longitudinal sections as obvious strands of chambered crystalliferous cells. Frequently strands of 6-8 unchambered non-crystalliferous cells appear. Paratracheal parenchyma is very few and difficult to observe.

The medullary rays - in cross section are two-sized and have a linear or slightly curved trajectory, and show obvious dilations at the boundaries of the growth rings. The two sized rays are: fine rays, 1-5-seriate, and thick rays, 10-17-seriate. The multiseriate rays have up to 200 μm wide and over 1 mm in height. The ray cells usually have the horizontal diameter of 10-18 μm, but frequently in the ray body appear wider, often with dark or bright-white content, and with white or black polygonal, slightly rounded, crystals. Their uniseriate endings have 1-5 high- er cells, somewhat similar to the uniseriate rays. Frequently, the rays are dissected by fibers or do not end fusiform but round, and in the cross section give strange aspects, probably caused by the cells exposure in other positions. Thinner rays are relatively low and can have up to 30 cells in the height. The ray frequency is 4-12 rays per horizontal tangential mm. Radially the 1-5 rows of marginal procumbent cells are slightly higher than the ordinary ones, or square or even upright 18-25(28) µm. The ray-body cells are usually procumbent, of 8-16-17 μm tall in the multiseriate rays, sometimes mixed with cells almost square of the same height and are empty or with solitary crystals. The normal thick-walled cells usually have dark content, and visible crystals. The similar crystalliferous cells of marginal rows appear to be hypertrophied. The unseriate rays usually have higher normal cells of 16-20-25 μm. The rays are relatively homogeneous and homocellular, with tendencies of heterogeneity. The cross-fields of rays with vessels show opposite half-bordered small pits, quasi-rectangular, rounded, elongat- ed up to scalariform, with diameters of 3-4 / 3.5-8 μm, on 1-2 (3) horizontal rows arranged.

The fibers in the cross section are slightly irregular arranged. They are polygonal, with a diameter of 8-10 μm, have very thick walls with very small, circular punctuation. On the vertical walls there are 3-5 μm small dots, vertically contiguous, sometimes difficult to observe.

Affinities and discussions

Not repeating the discussion of the precedent identified taxon, we must however show that the xylotomical details regarding the aspect and distribution of vessels, type and aspect of perforations, simple and/or scalariform, finely bordered pitting and the two sized rays observed in all these elven specimens studied here obviously fit with those of Fagaceae family, especially of Fagus L., sending to the fossil correspondent genus Fagoxylon (Stopes et Fujii) Süss, 1986 .

Süss (1986) revised and confirmed the validity of 11 species described until the date of the revision which are the following: Fagoxylon acerinum (Windisch) Süss, 1986 ; F. caucasicum (Felix) Süss, 1986 ; F. subcaucasicum Privé et Brousse, 1969 , found again by Privé-Gill et Watelet (1980); F. crystallophorum van der Burgh, 1973 ; F. francofurtense (Mädler) Süss et Müller-Stoll, 1984 ; F. grandiporosum (Beyer) Süss, 1986 ; F. hokkaidense (Stopes et Fujii) Süss, 1986 ; F. hondoense (Watari) Süss, 1986 ; F. kraeuselii Hofmann, 1948 ; F. mikofalvense Süss, 1986 ; and F. radiatum Süss, 1986 .

Thus, the xylotomic characters of our studied specimens compared with those of the cited species are the next: obvious growth rings; typically solitary vessels and short radial multiples or grouped, radial / tangential diameter of 50-90 / 35-60 μm, density of 70-300 vessels per mm 2, simple perforations and scalariform with 1-30 bars, intervascular pitting opposite to scalariform, parenchyma diffuse or in short line, two-sized rays: thin of 1-2 cells and thick of 10-17 cells, ray dilation at ring limit, homogeneity with tendency to heterogeneity, cross fields with half-bordered elongated to horizontal, opposite or slightly irregular scalariform, sometimes idioblasts with crystals present in rays, pitted fibers, irregularly arranged, or radial rows.

The comparison with the valid species of the Fagoxylon genus described (see Süss, 1986) showed similarity up to identity with the species F. crystallophorum van der Burgh, 1973 , although when it was described this species, the author (van der Burgh, 1973), did not gave a species diagnosis, considering the very good description, accompanied by the correct figuration (drawing, photomicrographs) quite suitable for comparative study. Thus, the semi-ring-porous wood described by the cited author presents solitary vessels or in irregular or ordered groups in tangential or radial thin rows, thick walled vessels with perforations simple and scalariform, sometimes reticulat- ed, and rounded to elliptic pitting to scalariform, sometimes irregularly arranged, tracheids accompanying vessels, parenchyma paratracheal, diffuse and in tangential uniseriate bands, having a cell diameter of 15-17 μm, or more, two-sized rays, slightly heterogeneous, with hypertrophied ray cells bearing solitary crystals and cells with very thick and pitted walls, aspects also found in our studied specimens. It is true that we have not reticulated perforations, but this is a more special character that probably does not have a very high incidence in the wood architecture.

From the table with biometric characters comparison ( Table 2), also results a high similitude with the species Fagoxylon crystallophorum van der Burgh, 1973 which determined us to attribute the here studied specimens to this species specifying that, in the cross sections, the appearance and layout of vessels, fibers, and parenchyma are identical to those given by Schweigruber (1990) for Fagus orientalis Lipsky even though in the longitudinal sections the differences do not appear to be too high of F. sylvatica L. species, as is also reported by Privé-Gill & Watelet (1980, p. 138). Thus, the studied material, consisting of 11 samples, is identified as Fagoxylon cristallophorum van der Burgh, 1973 .

Figures

Fig. 12 Fagoxylon cristallophorum van der Burgh, 1973. a, b - cross section: difuse-porous wood, two sized rays, ray dilation at the distinct growth-ring boundary - x50; c - cross-section: vessels, fibres, rays - x100; Photo d - tangential section: broad fusiform rays, high, disected, vessels - x100; e, f - tangential section: fusiform broad rays, scalariform perforation (e), scalariform intervascular pitting (f) - x200; g, h, i - radial section: scalariform piting on vessels (g), scalariform perforation (h), cross field with vessels (i) - x200.