Pinuxylon halepensoides van der Burgh, 1973

IAMANDEI, STĂNILĂ, IAMANDEI, EUGENIA, VELITZELOS, DIMITRIOS & VELITZELOS, EVANGELOS, 2022, Palaeoxylotomical Studies In The Cenozoic Petrified Forests Of Greece. Part Two - Conifers, Acta Palaeontologica Romaniae 18 (1), pp. 65-111 : 93-96

publication ID	https://doi.org/ 10.35463/j.apr.2022.01.07
persistent identifier	https://treatment.plazi.org/id/03E64438-B50B-FFFE-B003-FB2149E5C40D
treatment provided by	Felipe
scientific name	Pinuxylon halepensoides van der Burgh, 1973
status

Treatment

Fig. 10 View Fig , a-i.

Material

From the studied samples of petrified wood collected from Aegean area (insular part), 21 specimens showed a particular pinaceous xylostructure were selected. Those samples of silicified wood, were collected from early Miocene deposits from Lesbos : the samples Lsv.353, 354, 355, 356, 359, 362, 462, 539, 547, 550, 551, 555, 559, 560, 560a, 564, 569, 569a, 572, 579, and one from Limnos : Li.201. The studied material is registered as “Velitzelos Collection” and stored in the Collection of the Faculty of Geology and Geoenvironment , of the NKUA .

Microscopic description

Growth rings – relatively wide, often of more than 60 cells, showing quasi-gradual transition, but often abrupt or quite abrupt from the early wood to the late-wood, which has some rows of thick to very thick-walled tracheids, smaller and radially flattened, marking distinctly the ring boundaries. Normal axial resin canals of Pinus - type (described below) are present and appear isolated or in small groups usually in the late-wood. In some specimens (Lsv.353-356), the entire structures are invaded by large zoned crystals, and some dark remains, most

probably of secondary origin. Sometimes false growth-rings are present, suggesting probably climatic variations. Also, sometimes the early-wood appears collapsed, due to compression.

Tracheids – have moderately thick walls in the early-wood (3-8 μm the double- wall) and appear polygonal with slightly rounded corners and with radial / tangential diameters of 25-45 / 17-35 μm. In some specimens the cell walls are slightly corrugated. Toward the late-wood there is quite abrupt transition. The final late-wood comprises 6-13 rows of smaller and radially flattened tracheids of 8-18 / 5-15 μm in diameters and thick-walled, of 10-12 μm the double wall. Between two rays, 2-11 radial rows of tracheids can be counted, rarely more. The density is of 1100-1600 tracheids per mm 2. Intercellular spaces throughout the wood structure are present. Often, in transversal view, radial rows of narrower tracheids can be n between the normal ones. The pitting on the radial walls appears of abietineous type, of 18-20(-22) μm in diameter and with round apertures of 4-7 μm. The tracheidal pitting is usually poorly preserved, the pits are predominantly uniseriately arranged and appear spaced or contiguous, without crassulae. The pits are 1-2-seriately arranged, spaced or contiguous and without crassulae. No visible detail on the torus. On the tangential walls small, round to oval pits appear, of 8-12(15) μm in diameter, with small, round aperture, uniseriately arranged, spaced, and usually badly preserved. The length of the tracheids could not be measured, due to poor preservation. In longitudinal view, helical thickenings are absent but, sometimes, inclined striations were observed. Organic deposits as resin inside tracheids are often present.

Axial parenchyma – is absent.

Rays – are of two types: uniseriate rays, sometimes with some biseriate storeys, and fusiform rays 2-3(-4)-seriate, having 2-16(-20) cells in height, so they are of low to medium type. The fusiform rays are of 2-3 cells wide, have long uniseriate endings of 3-6 cells and bear 1-3 resin canals of 15-35 μm in diameter, with thin epithelial cells, usually destroyed. Their height is of 12-20 cells. Resin canals may appear in the uniseriate rays also. Lateral, triangular intercellular spaces are common. The ray density is of 9-14 rays on tangential millimeter. In radial sections the rays appear heterogeneous, showing two kinds of cells, all procumbent. The parenchymal cells are of 15-20 μm tall have smooth walls or slightly rough and unpitted, not too thick (2.5-3.5 μm double wall), but the tangential end-walls have 1.5-2 μm (simple wall) and are slightly nodular. The ray-tracheids are slightly taller and appear either inside the ray-body, or more commonly, are marginally arranged and often they are difficult to differenciate from the parenchymal body-cells, having smooth walls and unpitted and not too thick (2.5-3.5 μm double wall). When marginal, the ray-tracheids are taller, of 25- 35(-45) μm, and show slightly wavy outer wall, rough or with small thickenings to inside, suggesting tiny denticles. In the cross-fields, which are poorly preserved, can be guessed 1-3 pinoid pits of 8-10 μm (or with taxodioid aspect), horizontally arranged, having large, inclined, oval to lens-like apertures of 3-4.5 μm. In the taller cross fields, there can be more pits, up to 6, in 1-2 rows. On the ray tracheids the pits are rounded. Indentures are absent. Spiral thickenings are absent.

Radial resin canals – appear in the fusiform rays, but in the uniseriates also, as 1-3 narrow canals, among the ray-body cells, having 15-35 μm in diameter, and lined with thin epithelial cells, usually destroyed. Sometimes resin grains appear inside.

Axial resin canals – are present, with large, circular to oval cross section and appear isolated or in small groups, usually in the late-wood or close to it. The canals are relatively large-sized, of 75-250 μm the tangential diameter (150 μm mean diameter) and are lined by thin-walled epithelial cells which are often partially broken or destroyed. Traumatic canals absent.

Mineral inclusions – are usually absent but they were observed in some specimens (Lsv.353-356) as polygonal, large, zonated crystals, together with granular dark remains, irregularly arranged over all the structural elements. It ms that they formed secondary, during petrifying processes.

Affinities and discussions

From the studied material, 21 specimens with a similar pinaceous xylostructure and were grouped here by their particular features. So, they show in cross-section distinct growth rings, well developed, with thick-walled tracheids and axial canals lined by thin-walled epithelial cells, usually destroyed, which is typical for the secondary wood of Pinus-type (Greguss, 1955, p.121-123). Horizontal resin canals within fusiform rays are also present, and the rays are heterogeneous, with taller ray-tracheids with tiny denticles, detail which suggest a pine of Diploxylon-type, i.e. from subgenus Pinus L. (Ickert-Bond, 2001, p. 361). In some specimens (Lsv.353-356), the sections reveal large, zonated crystals or granular dark remains, most probably of secondary origin since the entire structure is invaded .

• Based on the supposition that the studied fossil pines are the ancestors of the current subtropical or Mediterranean pines, we tried a comparison with the current Pinus halepensis Miller , commonly known as the Aleppo pine (Earle, 2018), as xylotomically described by Esteban et al. (2010) since we observed some similarities to our specimens, like the quite thick-walled tracheids, even in the early-wood, with uniseriate radial and tangential pitting, with no crassulae. Also, the parenchyma is absent and in the uniseriate and fusiform rays appear 1-3 resin canals, cross-fields have 1-3(-6) piceoid to pinoid small pits and ray-tracheids have tiny denticles.

• All these details are present also in the species Pinuxylon halepensoides , an equivalent fossil species was described by van der Burgh (1973) and which have also

95 been identified and described by Dolezych (2005) and Dolezych & Schneider (2006) as having "not too thick walled tracheids, with radial pitting usually uniseriate, with pits relatively small, with no crassulae and with pitted tangential walls; parenchyma sparse or absent; rays uniseriate and low, the multiseriates having resin canals and ray-height of 10-12 cells. The walls of the ray-cells are thick and pitted. In cross fields there are usually one, rarely two piceoid to pinoid small pits of 6 μm. The ray-tracheids appear mostly marginal, and have serrations of medium size in their walls suggesting small denticles. Resin canals of Pinus type, with thin-walled epithelial cells are present" (Dolezych & Schneider, 2006).

• Esteban et al. (2010), studying the current species Pinus halepensis , remark a great similarity with Pinus brutia Tenore , another Mediterranean species with xylostructure close to our studied specimens, having, for example, the axial resin canals located only in the late-wood. In fact, both Pinus halepensis and P. brutia have very similar woods and separating them with wood natomical features are almost impossible (Schweingruber, 1988; Akkemik and Yaman, 2012). For that reason, both two species may be evaluated in their fossil forms, as Pinuxylon halepensoides .

• In fact, long before them, Greguss (1955, p. 231) described Pinus halepensis and P. brutia , specifying that “there is no difference in the walls of early and late tracheids”, refering to their thickness, and “teeth barely emerge from the walls of transverse tracheids”, detail similar to our studied specimens. Also, Greguss (1972, p.127) has described Pinus brutia var. eldarica Medv. as having beside the typical features of the species, "thick walled to very thick-walled tracheids from early- to late wood", which is quite similar to our studied specimens. Anyway, this difference is not clear even in modern woods (Akkemik, 2021, pers. communication).

• Moreover, the short descriptions and figuration presented in Schweigruber (1990), Akkemik & Yaman (2012) and Crivellaro & Schweingruber (2013) for Pinus brutia are very similar to our studied material.

Our specimens present very similar xylotomy to the original description of Pinuxylon halepensoides and, also, to the description of the curren species Pinus halepensis as presented above after Esteban et al. (2010), compiled with those of other authors cited above, having axial canals isolated or in small groups, usually in the transitional and late wood and sometimes, close to ring boundary, heterogeneous rays with canals, crystals. Based on this discussion on the affinities of the xylotomy of the studied specimens, we decided to attribute all of them to the fossil species Pinuxylon halepensoides Van der Burgh, 1973 .