Aceroxylon zarandense, Iamandei & Iamandei, 2017

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 : 77-78

Aceroxylon zarandense sp. nov.

Fig. 17 , photos a-i.

Material

From a sample of dispersed petrified wood (field number 26), collected from Prăvăleni area from the left side of Prăvăleni valley at the confluence with BodiȘteanu brook from Mid-Miocene volcano-sedimentary deposits (Late Badenian-Early Sarmatian). The centimetric sized samples representing a silicified wood fragment of whitish-beige color with brownish and is kept now in GIR collection at National Geological Museum - Bucharest under the inventory number 26,279 (field number: 26). Under the magnifying glass fibrous structure can be seen, distinct annual rings, short thin and sinuous medullary rays, and vessels, typical for a dicotyledonate wood.

Microscopic description

The growth rings are relatively distinct in cross section, not very wide, the boundary marked by the presence of a terminal wood made up of mainly ground tissue. Otherwise, the structure is diffuse-porous, smaller vessels appear only in the close proximity of the terminal wood, and the rays are slightly dilated at the boundaries of the annual rings.

The vessels in cross section are solitary and in radial multiples of 2-3, or groups of 4-5 pores. The solitary ones have an oval or circular cross section and show sometimes solid brown deposits. The walls are moderately thick of 4-8.5 μm double wall. The radial / tangential diameters for solitary pores are of 42-75(84)/42-51(60) µm and their density is 35-60(85) vessels per mm 2. The vessels have simple perforations on inclined plates. The vertical walls of vessels, especially of those vessels with lower lumen, exhibit relatively thick spiral thickenings, with repeated and obvious turns. Rounded to oval bordered pitting, relatively numerous, small of 4-7 μm, alternate to sub-opposite without touching each other, with circular apertures of 2-3.5 μm in diameter horizontally elongated or point like. The average length of the vascular elements is 500-640 μm. Inside vessels, rarely large thin walled tyloses appear.

The axial parenchyma - is of apotracheal type, a few short or long uniseriate lines interleaved with fibers, constituting the terminal bands of 3-4 cells thick, which are marking the distinct boundary of the growth ring. It occurs also diffuse, as cells dispersed among the fibers within the annual ring, and also as vasicentric uniseriate. In the longitudinal sections the parenchyma consists of nearly square empty rectangular cells in vertical strands of over 8 cells, pitted and sometimes with solitary crystals.

The medullary rays - in cross section appear 1-3(4)- seriate, and have a special behavior: the thicker rays have continuity on 2-3 annual rings, the uniseriates have continuity only on an annual ring. Near the vessels they have a slight inflection and may come in contact with them, but generally have a linear trajectory, and the thicker ones show a slight dilation at the boundary of the growth ring. Also, the cells have a dark content. In tangential section, the uniseriates appear relatively numerous, they have 3- 12 cells in height (up to 125 μm), the ray cells round or slightly vertically elongated, mixed. The 2-4-seriates rays have 15-77 cells in height, that is, 192-500 μm and have uniseriate endings of 1-8 rounded cells, the last being narrower and elongated. The ordinary ray body cells tend to be more rounded and more equal in size (8-11 μm), and contain residual gums. Sometimes marginal, noticeably larger rounded cells (of 15-24 μm in diameter) and brighter, which appear to be mucilaginous cells. The frequency is 8-10 rays per horizontal tangential mm. Radially the rays are homocellular, formed from procumbent cells whose length varies from the early to late wood, when the cells can be squared with the same height. Ray cells have very small spaced pits of 2 μm on two rows in the early wood, or a single, larger, round or oval pit with small circular aperture, in the late wood. Sometimes, the ray cells contain large, solitary crystals.

The fibers have a polygonal cross section of 15-20 μm in diameters, relatively thick walled of 4-6 μm, especially in the late wood made up of 6-10 radial rows. Vertically are pitted and sometimes have long rows of crystals.

Affinities and discussions

The xylotomical characters observed in this specimen are very similar to those described by Metcalfe & Chalk (1950), Greguss (1959), and Schweingruber (1990) for members of the former Aceraceae family, especially of Acer type, now belonging to the Sapindaceae family, the Hippocastanoideae subfamily ( APG IV, 2016).

We do not repeat the discussion on the affinities of the specimens described above to whom also we have seen similitudes, but note the description of the generic xylotomic characters of the Acer genus from Schweingruber (1990), which is more similar to our specimen description: the obvious growth rings, marked by some rows of flattened fibers, the diffuse-porous wood, with spaced solitary pores or as short multiples, with simple perforations, alternate pitting and spiral thickenings with diffuse apotracheal parenchyma, occasionally paratracheal, rarely terminal, slightly dilated rays at the ring boundary, 1-3-5(6)-seriate, of 40-50(60) cells high, homocellular, cells all procumbent, rarely marginals square with increased pits.

Comparing the xylotomy of our specimen with the fossil aceraceous species previously described, including the species described in this paper, we think we have studied here a wood structure more similar in terms of distribution and shape of the vessels, parenchyma, fibers and rays, the type of perforations, pitting and spiral thickenings with the current species Acer cappadocicum Gled , a species with a living area comprising the southern regions of Central and Eastern Europe and Asia , a maple native to central Turkey (ancient Cappadocia), east along the Caucasus , the Hymalaya, to southwestern China, areas marked by a temperate to warm-temperate climate up to the subtropical of the Mediterranean wetlands .

An advanced comparison with respect to other fossil forms described until present maybe could suggest a possible identification, but in the present case we believe we are in the face of a new species, which we named Aceroxylon zarandense sp. nov., according to the name of the region where it was found the holotype (inv. no. 26,279), as a fossil equivalent of the extant maple Acer cappadocicum . The material studied here was initially wrongly identified as a member of the Meliaceae family (Iamandei & Iamandei, 1998), with which it has possibly similar features, but the revision of the original material and the taxonomic reidentification, have denied the assignment of this specimen to the Carapoxylon cf. porosum (Felix) Mädel, 1960 .

Diagnosis of Aceroxylon zarandense sp. nov.

( Holotype: inv. no.: 26,279 kept now in GIR collection at National Geological Museum - Bucharest) .

Secondary wood diffuse-porous with relatively distinct growth rings, marked by slightly flattened terminal fibers and dilated rays at ring boundary. Vessels solitary and in radial groups of 2-3(5), the solitary oval or circular in cross section, of 42-75(84) / 42-51(60) µm, and thick-walled of 4-8.5 μm double wall, density of 35-60(85) vessels on mm 2, simple perforations, spiral thickenings frequent and relatively thick, bordered pitting, pits round to oval, numerous, alternate to sub-opposite without touching each other, small of 4-7 μm, with circular apertures of 2-3.5 μm to horizontally elongated, or point like. The vascular elements have 500-640 μm in length, large thin-walled tyloses inside and solitary crystals or colored crystal-sand. Parenchyma apotracheal diffuse, as short or long uniseriate bands interleaved in the latest wood, and rarely paratracheal. Vertically the parenchyma appears as near square empty cells in vertical strands of 2-4 cells, sometimes pitted and with crystals. Rays 1-4-seriate, the uniseriates of 3-12 cells tall, the 2-4-seriates fusiform, of 15-77 cells tall, with endings of 1-8 cells. In the ray-body sometimes larger mucillaginous cells appear. Ray frequency is of 8-10 rays on tangential mm. Rays homocellular, with ray-cells all procumbent, sometimes square, with spaced simple, very small pits, of 2 μm, on two rows arranged in the cross-fields with vessels and with solitary crystals. The fibers have polygonal section of 15-20 μm in diameter, thick walls, spiral thickenings, septa, and rare, small, simple pitting in a vertical row.

Figures

Fig. 17 Aceroxylon zarandense sp.nov. a - cross section: diffuse-porous wood, solitary and small grouped vessels, two sized rays with slight dilation at the ring boundary - x50; b, c - cross-section: fine and multiseriate rays with slight dilations at the ring boundary, solitary and grouped vessels - x100; d - tangential section: fine and multiseriate fusiform rays, tall, vessels with tilted simple perforated plates - x100; e-f - tangential section: remains of spiral thickenings and badly preserved pitting (e), intervascular alternate pitting - x200; g, h, i - radial section: simple perforations (h), bad preserved cross-field (i), bad preserved alternate pitting (g, h) - x200.