Rhysocaryoxylon sp.

Iamandei, Stanila, Iamandei, Eugenia, Velitzelos, Dimitrios & Velitzelos, Evangelos, 2024, Palaeoxylotomical Studies In The Cenozoic Petrified Forests Of Greece. Part Three - Dicots, Acta Palaeontologica Romaniae 20 (2), pp. 61-96 : 88-89

Rhysocaryoxylon sp. aff. Juglans regia L.

Fig. 13 , photos a-i

Studied material. Other 21 samples of silicified wood, collected from Evros, from late Oligocene to early Miocene volcano-sedimentary deposits, showed a special juglandaceous xylostructure of Juglans type, marked by the presence of non-crystalliferous axial parenchyma. They are kept in the Collections of the Faculty of Geol. & Geoenviron. of NKUA, registered under these field numbers: Spp32, Spp34, Spp1074, Spp1075, Spp1076, Spp1078, Spp1079, Spp1080, Spp1082, Spp1083, Spp1084, Spp1085, Spp1086, Spp1087-32, Spp1088, Spp1089, Spp1090, Spp1091, Spp1091-31, Spp1092, Spp1093, Spp1094, Spp1098, Spp1100, Spp1101, Spp1102, Spp1104, Spp1105; Spp1106, Spp1107, collected from Sappes; one more, Lgn167, collected from Lagyna; and two collected from Trifili, Tf12, Tf13 .

Microscopic description. The growth rings – in cross-section appear with diffuse-porous to semi-porous aspects with less distinct ring boundaries, marked by a few smaller and slightly flattened ground-tissue cells of final wood, suddenly followed by the early-wood with normal sized ground tissue cells, where the larger vessels of the early-wood also appear. And, is to be remarked that, in cross-section, the rays often have a very ondulate trajectory and the axial parenchyma is few, is non-crystalliferous and, sometimes, appears as short, discontinuous, tangential bands.

The vessels – appear solitary or in small radial groups, defining a wood of diffuse-porous to semi-ring-porous type of structure, represented by quasi-equally-sized vessels in all the growth-ring, sometimes slightly diminishing in the late-wood. Vessels’ arrangement shows a radial pattern between two successive rays, but show a diagonal aspect in multiple neighboring interradial bundles. They appear commonly solitary (60% or more) and/or grouped in radial multiples of 2-4(-6). The shape of the solitary vessels is rounded or radial oval, slightly deformed when grouped. The solitary vessels have the lumina size of 75-150 / 50-100 μm the radial / tangential diameter, (decreasing to 30-60 / 20-50 μm in the late-wood). The vessel wall is not too thick, we measured 6-8 μm the double wall. In the longitudinal view, the vessels show exclusively simple perforated plates. The numerous intervessel pits of bordered type are contiguous and alternately arranged. The pits are mean-sized, of 8-10 µm diameter. The vessel-ray pits are similar, have much-reduced borders, and are smaller sized, corresponding to the cross-field pitting, described below. Helical thickenings in the vessel elements are not present. The mean tangential diameter of vessel lumina is around 85 µm. Vessels' density up to 20 vessels per sq. mm. or more, counting all the vessels as IAWA recommended (see Wheeler et al., 1989). The mean vessel element length is between of 350-500 µm, or more. Also, inside the vessels' lumina, sometimes, thin-walled tyloses and dark content can be seen. Tracheids – or vascular fibres or vasicentric tracheids usually absent .

The fibres – not very thick-walled, represent the major part of ground tissue, are minutely bordered pitted on the vertical walls, and are not septate, but difficult to observe, due to poor preservation.

The axial parenchyma – in cross section appears few, as apotracheal, diffuse among fibres or as narrow (1-2- seriate), short or discontinuous tangential bands, not crystalliferous and, also, few paratracheal appear.

The rays – after their width are fine rays, usually 1-2(-3)- seriate and have often an ondulate trajectory. The ray height is usually low to high. The analysis of ray-cellular composition shows rays of homocellular type, slightly tending to heterocellular: the body ray-cells are all procumbent and have 1-2 rows of square or procumbent marginal cells, slightly taller. In cross-fields with vessels, appear pits with much-reduced borders to almost simple, are polygonal and mean-sized, alternately arranged, in 2- 3 superposed rows in taller cross-fields. But often they are less visible, because of dark content or poor preservation. The rays are devoid of sheath-cells or of tile-cells. The ray density is between 10-13 rays/mm.

Storied structures – absent. Secretory elements – as oil/mucilage cells absent. Intercellular canals – not present. Cambial variants – as included phloem not observed. Mineral inclusions – are absent.

Affinities and discussions. A large number of specimens from the studied material showed a similar juglandaceous structure of Rhysocaryoxylon type, but slightly different from the above-described species, grouped here as having, in cross-section, a diffuse porous to semi-porous structure; with non-crystalliferous axial parenchyma few, diffuse among fibres or as narrow, short and discontinuous tangential, fine bands, but not in a reticulate arrangement. These features, besides the arrangement and size of the vessels in cross-section, as well as exclusively simple perforations and alternate bordered pits on vertical walls, could have a taxonomic value, as presented by Greguss (1954), Dupéron (1988), Schweingrüber (1990), Schoch et al. (2004), Wheeler et al. (2011) and Akkemik & Yaman (2012).

More details are presented above, at the identified species, regarding to the xylotomical features of the main current and fossil juglandaceous valid genera, as summarized by Dupéron (1988), Blokhina (2007) and Sakala & Gryc (2011). These authors discussed, especially, the presence or absence of the crystalliferous parenchyma in the structure, as well as the thickness of the vascular wall.

Thus, we observe the here studied specimens possible similarities of the xylotomy with the current species of Juglans L. The species Juglans nigra L., known as „Black North- temperate Walnut“ - which has crystalliferous parenchyma, as short vertical chains of no more than 5 chambers with solitary crystals, so it is different from the here studied specimens. The species Juglans regia L., (also known Gray Walnut, Persian walnut, Madeira walnut, Carpathian walnut, English walnut or common walnut), has a xylotomy more similar to our studied specimens. It is native to southeast Europe to central Asia, a region stretching from the Balkans eastward to the Hymalayas and southwest China ( Juglans regia - Wikipedia - accessed 05.02.2023).

The correspondent fossil genus, Rhysocaryoxylon Dupéron, 1988 includes in its diagnosis, the porous to semi-ring-porous structure, thick-walled vessels with simple perforations and intervascular pitting polygonal, alternate. The parenchyma apotracheal few, diffuse among the fibres or as narrow discontinuous bands is usually not crystalliferous and the rays are 1-3(5)-seriate and heterogeneous.

Considering the details observed in here studied specimens, as the diffuse-porous to semi-porous structure in cross-section, the non-crystalliferous axial parenchyma few, diffuse among the fibres, or as narrow, short and discontinuous tangential, fine bands, but not in a reticulate arrangement well as the comparison with other described European fossil species, we decided to assign them to Rhysocaryoxylon sp. aff. Juglans regia L., probably representing a fossil correspondent of the current Juglans regia L. (i.e. Gray Walnut), a native mediterranean species, still living in this region, from Balkans, eastward, to Himalaya.

Figures

Fig. 13. Rhysocaryoxylon sp. aff. Juglans regia L. (Specimen Spp1105). a–c. Cross section – semi-ring porous structure, quite indistinct growth-rings, parenchyma diffuse or as short or discontinuous tangential bands; d–f. Tangential section –1-3(4) seriate rays; g–i. Radial section – simple perforations; heterocellular rays with 1-2 square or upright marginal cells; pitting in cross fields. photos a-i (graphic scale).