Pinuxylon sp.
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publication ID |
https://doi.org/ 10.35463/j.apr.2022.01.07 |
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persistent identifier |
https://treatment.plazi.org/id/03E64438-B508-FFC3-B3A4-F8CF49F4C75A |
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treatment provided by |
Felipe |
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scientific name |
Pinuxylon sp. |
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Pinuxylon sp. aff. Pinus canariensis C. Sm.
Fig. 11 View Fig , a-i.
96 Material
Some samples of petrified wood showing similar pinaceous xylostructure, were grouped as having parenchyma of a special type. These four samples with field numbers Lsv.4, 357, 389, 543 represent fragments of petrified (silicified) wood and were collected from Lesbos Island . 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 – are well developed, wide of more than 60 cells, with gradual transition from early- to late-wood, sometimes quite abrupt and with distinct growth-ring boundaries, in cross-section. Normal axial resin canals of Pinus - type are present, with thin-walled epithelial cells often destroyed and accompanied, sometimes, by some axial parenchyma as subsidiary tissue, details described below. The wood structure is quite compressed in the early wood, or is locally collapsed.
Tracheids – are relatively thin-walled in the early-wood, showing a quasi-polygonal cross section, large and often deformed by compression and show slightly corrugated walls. They have radial / tangential diameters of (25)40- 60 / (20)35-50 μm, and wall thickness of 4-6 μm (double wall), in the early wood. When transition is gradual a well-developed transitional wood is visible, with tracheids relatively thicker-walled (of 6-8 μm the double wall), and their cross-section is of 10-20 / 20-30 μm in diameters (ra/tg), gradually diminishing to the final rows of late-wood where they appear as radially flattened cells, thick-walled (8-10 μm the double wall), marking the growth-ring boundary. Between two successive rays 1-9(- 15) radial rows of tracheids were counted. Sometimes radial rows of smaller tracheids are intermingled. The tracheid density is around 1500 tracheids per mm 2. In longitudinal view, the tracheids present 1(-2)-seriate pitting on the radial walls, more or less contiguous, sometimes with crassulae. The pits are of abietineous type, are 17-24 μm in diameter and round apertures of 4-5 μm. Because of poor preservation, no visible details on torus were n. On the tangential walls, a few, uniseriate, small round pits of 5-8 μm in diameter and with small round aperture were observed. Organic deposits inside the tracheids are often present as resinous plugs or sometimes irregular dark patches covering other structural elements also. Tracheids’ length could not be measured. Intercellular spaces often present. Late-wood tracheids - thick walled. Helical thickenings on tracheids absent.
Axial parenchyma – is exceptionally present, either as some parenchyma cells more or less accompanying the axial canals as a subsidiary parenchyma either aliform, or as diffuse small insular groups of moderately thick-walled cells, with some granular content of resin or starch. In longitudinal view they appear as groups of rectangular cells.
97 Rays – are of two kinds: uniseriate and multiseriate. The uniseriates have sometimes some biseriate storeys and can have up to 16 cells high or more, the average height is of about 180 μm. The fusiform rays are 2-3 seriate with uniseriate endings of 3-6 cells, having 15-20 cells in height and can include 1-3 resin canals. Lateral triangular intercellular spaces are common. Ray density is of 17-18 rays per tangential millimeter. In radial view the heterogeneous character can be observed. Thus, beside the parenchymal body-cells have 10-15(-18) μm in height, ray-tracheids appear, either inside the ray-body or marginally arranged and sometimes difficult to differentiate them from the other ray-cells, since they resemble. The horizontal walls of the parenchymal cells are smooth or slightly rough and probably pitted and are relatively thin-walled (2-3.5 μm double wall), while the tangential walls (the end-walls) are thin, of 1.5-2 μm the simple wall and smooth or slightly nodular. The indentures are missing. The ray-tracheids are slightly taller, of 25 μm or more, and show harsh horizontal walls, sometimes with small thickenings suggesting tiny denticles and, when marginally arranged, have the outer wall slightly wavy. Helical thickenings were not observed. In cross fields the pitting appears as 1-3(4) pits or more in 1-2 rows horizontally arranged. They are small inclined pinoid pits, or piceoid to taxodioid, of 9-11 / 5-8 μm in diameters, with lens-like apertures, of 3-4.5 μm. On the ray- tracheids they are slightly rounded. Often the cross-field pitting is difficult to observe due to bad preservation or to presence of organic content.
Radial resin canals – appear as 1-2(3) inside the ray-body, are narrower, of 10-17(25) μm in diameter (average diameter 14-15 μm). Resin grains can be observed inside them. The epithelial cells are usually destroyed, or less visible.
Axial resin canals – are of Pinus - type and have circular or slightly oval shape in cross section. They appear usually isolated or in small groups in the growth ring, often in the early wood, but also in transitional toward the late wood. The canals are quite large, of 150-200-350 / 120- 250 μm the radial / tangential diameter, sometimes with resin-remains inside and are lined by the thin-walled epithelial cells sometimes with starch grains inside, often destroyed. The canals are accompanied by subsidiary tissue, sometimesc with aliform aspect. Traumatic canals are absent.
Mineral inclusions – absent but sometimes starch grains appear, inside radial or axial parenchyma.
Affinities and discussions
Four samples of petrified wood collected from Lesbos Island, all sharing a special pinaceous wood structure which, even if poorly preserved, is characterized by the presence of axial resin canals of Pinus - type, lined by thin epithelial cells. These axial canals are often accompanied by groups of parenchymal cells, most probably representing a subsidiary tissue, similar to that described by 98
Esteban et al. (2005) for the xylostructure of Pinus canariensis C. Sm. , an evergreen subtropical pine, endemic now in Canary Islands were grows at 1500-2000 m altitude (Earle, 2018). In radial section, our specimens present heterogeneous rays with taller ray-tracheids and with rough horizontal walls or even slightly dentate, detail which confirms that it is a pine of Diploxylon - type, from subgenus Pinus L., (Ickert-Bond, 2001 and Gernandt et al., 2005).
• Greguss (1955, p.232) made a short description of the xylotomy of Pinus canariensis C.Sm. , noting that this pine native to the Canary Islands and has a great xylotomical similarity to Pinus halepensis Mill.
• However, Esteban et al. (2005) doing a very detailed xylotomical study of Pinus canariensis , have described a lot of microscopical details that are very specific and useful in wood identification of this pine, as follows: "Growth rings distinct, with relatively gradual change. Axial resin canals with thin epithelial cells bearing starch grains and located in the transitional-wood or in the late-wood, rarely in the early-wood and having mean tangential diameter of 221 μm. Tracheids with irregular to hexagonal or square cross-section, of 40-50 μm and with intercellular spaces. Large radial pits, of 24 μm, 1(-2)-seriate and with crassulae. Tangential pits not observed. Parenchyma as subsidiary tissue appear, close to axial canals, in aliform to confluent or diffuse groups, bearing starch grains. Rays uniseriate of 2-32 cells high, and fusiform multiseriate rays with resin canals, heterogeneous and homocellular. The thick-walled rayparenchyma cells with horizontal walls pitted and end-walls smooth, with high content of starch grains and cross field pits of pinoid type, 1-2(-4) per field. The ray-tracheids appear marginally or in ray-body, with irregular thickenings sometimes as small dentations and smaller pits".
• As already suggested by the presence of subsidiary tissue, sometimes of aliform type, also observed in our studied specimens, most likely we talk about a fossil pine with many xylotomical affinities with Pinus canariensis , as described by Esteban et al. (2005). Microscopic observation revealed other similar details, but the presence of the typical subsidiary tissue definitely indicates affinity of our studied specimens to the above specified pine.
• Recently a new Miocene fossil pine species, from eastern Turkey, was described as Lesbosoxylon kemaliyense Akkemik & Mantzouka (in Akkemik et al., 2020a). The specific diagnostic features of the new species are: transition from earlywood to latewood mostly gradual; axial and radial resin canals with thin-walled epithelial cells; latewood tracheids thin to thick walled; bordered pits on radial walls of tracheids 1-2(-3) seriate; crassulae common; rays uniseriate, partly biseriate; uniseriate rays up to 27 cells high; fusiform rays up to 30 cells high; axial parenchyma occasionally present; ray tracheids 2-3 rows; cell walls of ray tracheids smooth; cross field pitting pinoid, 1-2(-6) pits per cross field. Anyway, after detailed investigation of the botanical affinities of the new fossil wood, it is suggested that the most closely related modern species is Pinus canariensis . This “living fossil” could be close to our described specimens, but it is slightly different by having higher rays and no typical subsidiary tissue, even if is noted in description: "axial parenchyma is occasionally present".
• In another recent study, Akkemik et al. (2021) described from Turkey a mid Eocene pine with parenchymal cells around the resin canals interpreted as subsidiary tissue and identified as Pinuxylon cf. P. tarnocziense (Tuzśon) Greguss and could be similar to our specimens.
Therefore, taking into account the above discussion on the xylotomical similarity of the studied material with the structure of the current Pinus canariensis , (in Esteban et al., 2005), with weakly dentate ray-tracheids, large axial resin-canals of Pinus type with thin-walled epithelial cells, and accompanied by aliform subsidiary tissue, we assign our studied specimens to Pinuxylon sp. aff. Pinus canariensis C. Sm. since we had few specimens in study, rather poorly preserved, with not enough xylotomical details to identify a known species or to describe a new one.
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