Piranheoxylon perfectum, 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 : 72-75

Piranheoxylon perfectum sp. nov.

Fig. 15 , photos a-i.

Material

From a sample of dispersed petrified wood collected from Prăvăleni area, from Cremenea Hill (field number 171) from Mid-Miocene volcano-sedimentary deposits (Late Badenian-Early Sarmatian). The centimetric sized sample represent a silicified wood fragment of beige color or beige with rusty tint and is kept now in GIR collection at National Geological Museum - Bucharest under the inventory number 26,354 (field number: 171). Under the magnifying glass fibrous structure, less distinct annual rings and visible vessels and rays can be observed, suggesting dicotyledonate wood.

Microscopic description

The growth rings are less distinct in the secondary wood, slightly marked by terminal (latest) parenchyma as tangential discontinuous bands of 2-9 cells thick, devoid of vessels and rays slightly dilated at the limit of the annual ring. Some local traumatic aspects (as disorganizations) disturb the porous wood structure.

The vessels are usually solitary and in radial multiples also or irregular groups of 2-5, sometimes with tangential pairs included, defining a porous wood type. Sometimes the vessels are separated by a short radial row tracheid, or radially continue with 1-5 smaller vessels or vascular tracheid. The solitary vessels have polygonal-rounded or oval shape, sometimes irregular or star like, even crushed in the disorganized areas. The vascular walls are moderately thick, of 4-8 μm double wall. The lumen of solitary vessels has the radial / tangential diameters of 40-80(96) / 40-50 μm (mean values: 52 / 42 μm). The pores' size is relatively constant within a growth ring, from which the appearance of diffuse-porous wood and the density is 64- 90 pores per mm 2. The vessels have scalariform perforations relatively high, with 8-30 bars, sometimes corrugat- ed, with bifurcations and vertical anastomoses. The pitting is scalariform or with oval bodered pits, opposite or horizontally elongated, often coalescent to scalariformes and numerous, especially on the the vessel endings, since the vascular elements have length of 450-975 μm and present high "tails". Sometimes very short vessel elements, of 80-90 μm, appear. Frequently spiral thickenings on the narrower vessels appear and also on the vessel tails and even on the thicker vessel body. On some vessels, rare, large tyloses appear and content of granular gums isolated or agglomerated up to compact, clogging the lumen. In addition, fungi as hyphae and fruiting corps appear.

The axial parenchyma - is very few, diffuse or of scanty-paratracheal type as 1-2 (3) cells, crushed to the vessels, and as discontinuous bands of 2-9 cells in the latest wood, sometimes with cells wider than the fibers. Vertically is relatively difficult to detect, it occurs in strands of 6-8 vertical rectangular thin-walled cells, with rare simple pits, irregularly arranged. The terminal parenchyma appears as bundles of numerous rectangular vertical cells (more than 16), storied. Sometimes dark granular gumremains of and hyphae and fruiting corps of fungi are present. Dispersed among the fibers, chambered cells with rounded solitary crystals inside appear.

The medullary rays are uni- or biseriate, rarely triseriate, and in cross section appear constituted by radially elongated rectangular cells. The rays have linear trajectory and slight dilations and deviations at the annual ring boundary, and sometimes touch vessels. Tangentially they are frequently tall, of 2-52 cells in height or more (i.e. up to 1270 μm), compact and rarely articulated. The uniseriate rays have sometimes short biseriate storeys, with pairs of the same thickness as the uniseriate part. The ray-body cells appear rounded to polygonal and the uniseriate endings consist of 1-12 vertically elongated cells, the last being more elongated triangular. The frequency is 7-10 rays per mm tangential. Radially the rays are heterocellular, the ray-body cells having all procumbent cells, of 16-18 μm in height, and the marginals slightly higher or even upright, of 18-32 μm. In the cross fields with vessels the pitting is round or elliptical, to scalariform of 5-6.5 / 8-11 μm especially on marginal fields. In the ray cells also 1-3 crystals or more and gum remains appear.

The fibers - in cross section appear arranged in 1-15 radial rows between two successive rays. The fiber cells are moderately thick-walled, 4-5.5 μm double wall, and have a polygonal section rounded at the corners, causing frequent triangular or rhombic intercellular spaces, and have large polygonal-rounded lumina, of 8-25 μm. Often there are narrower fibers dispersed among the others, which sometimes can be confused with the intercellular spaces, since often they form discontinuous radial rows. In the areas with disorganized structure the fibers are also deformed, even crushed. Vertically, inside fibers, the septa are rare, and the longitudinal walls have rare pits in an irregular row.

The fibrotracheids have vertical bordered oval pitting to slightly horizontally elongated, even scalariform on the vascular tracheids of the rows with narrow vessels from the complex multiples of large vessels already observed in the cross section. They are obviously wider than the ordinary fibers and even the length of the tracheidal elements is smaller (length 40-250 μm, diameter 15-28 μm).

Affinities and discussions

The xylotomic characters of the studied specimen are similar to those of the "euphorbiaceous" woods of "phyllanthoideae group" type as it is presented in Metcalfe & Chalk (1950) and in Mädel (1962), and in a first instance would appear that genus Securinega is xylotomically similar to our specimen since it presents scalariform perforations, but also another "euphorbiaceous" genus, namely Piranhea . However, using the old taxonomy Metcalfe & Chalk 1950 (p. 1222) separated the Phyllanthoidee from a group of special characters (called "other phyllantoideae") that includes the current genera Piranhea , Uapaca , Savia , Androstachys , Breynia, Dissilaria , Longetia , Mischodon , Oldfieldia , Petalostigma , whose xylotomic characters appear to match those of our specimen.

Comparing our specimen with the fossil correspondent genus Piranheoxylon Grambast, 1961 which was created based on a species described from the Eocene of Belgium ( Piranheoxylon stockmansi Grambast, 1961 ), we found many similitudes related to the shape, size and distribution of the vessels in cross-section, the types of pitting and the perforations, the type of parenchyma and the presence of the crystalliferous chambered parenchyma cells, the type, the height and the cellular composition of the rays as well as the appearance of the fibers.

Our specimen has also some specific characters such as follows: the presence of growth rings marked by 2-9 cell parenchymal terminal bands, the slight dilation of the rays at the ring boundary, the predominant scalariform pitting, spiral thickenings on the vessel tails, on the narrow and on the large vessels also, the crystalliferous unchambered ray-cells, ray usually biseriate, higher, with elliptic to scalariform pitting on the marginal cross fields, fibers thick-walled, with polygonal-rounded section, oval elongated to scalariform pitted.

Following this critical discussion we believe that the studied specimen is a new species which we have named Piranheoxylon perfectum sp. nov., for the perfection of the anatomical details offered.

Diagnosis of Piranheoxylon perfectum sp. nov.: Porous wood with less distinct growth rings and terminal parenchyma. Solitary vessels and in radial multiples with indentations, and in irregular groups of 2-5 small vessels and tracheids, fibrotraheides. Solitary vessels roundedpolygonally shaped, to oval or irregularly star-like with moderate thick walls, radial/tangential diameters of 52/42 μm, density of 64-90 pores on mm 2. Scalariform perforations, storied, with 8-30 thin bars, corrugated, bifurcated and anastomosed. Intervascular pitting scalariform or oval bordered to horizontally elongate up to scalariform pits. Vascular elements length of 450-975 μm, having spiral thickenings on the high tails and tyloses. Parenchyma diffuse, scanty-paratracheal and in discontinuous bands in the latest wood. Storied vertical strands of 6-8- 16 cells with simple pitted walls, and chambered with rounded crystals inside. Rays 1-2(3)-seriate, with platanoid dilations, of 2-52 cells in height, uniseriate, with short biseriate storeys of the same size as uniseriate. Radially the ray cells appear all procumbent, with 1-12 marginal rows of slightly higher or even upright cells and with round or elliptical pits to scalariformes. Ray frequency is 7-10 rays on tangential mm. Often 1-3 or more crystals on fields and gums appear. Fibers with rounded polygonal large section of lumens (8-25μm), relatively thick walled, severed, rare septa and irregular pitting. Fibrotracheids and vascular tracheids with oval bordered pits, elongated to scalariformes.

Figures

Fig. 15 Piranheoxylon perfectum sp. nov. a - cross section: diffuse-porous to semi-ring-porous wood, solitary and grouped vessels - x50; b, c - cross-section: 2-3-seriate rays with obvious dilations at the ring boundary, solitary vessels, thick-walled fibres - x100; d - tangential section: biseriate rays, tall - x100; Photos e-f - tangential section: scalariform intervascular pitting - x200; g - radial section: storeyed scalariform perforations - x100; h, i - radial section: scalariform perforation (h), crossfields with numerous scalariform piting - x200.