Glyptostroboxylon tenerum (Kraus) Conwentz 1884

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 : 86-89

Glyptostroboxylon tenerum (Kraus) Conwentz 1884

Fig. 8 , a-i.

Material

The fossil material studied, represented by 53 samples of silicified wood, comes from Aegean area - insular and also continental part. Thus, some of them were collected from Evros, from late Oligocene volcano-sedimentary deposits, from Lefkimi - the samples with the field numbers Lfk.153, 155, 157, 166, 174, 190, 191, 254, 264, 271, 275, 283, 290, 291, 292, 293, 295, 296, 297, 299, 301, 302, 308, 310, 318, 321a, 321b, 325, 328b, 333; and from Trifili - the samples Tf.1, 2, 7, 9a, 14, 16, 30, 109, 119. Also, other samples were collected from early Miocene volcano-sedimentary deposits from Limnos Island – the samples Li.187, 193, 194, 197, 200, 209, 230, 236, 467, 469, 473, 483, 484, 485a. 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 – show a variable width, from low to often large of over 50 cells, with quite abrupt transition, even if sometimes a gradual size diminution is visible, from the early-wood to the late-wood, which is represented by 2-5 rows (sometimes more) of smaller flattened cells, and the growth rings boundaries are quite distinct, since the early woodalways starts with larger cells. Normal resin canals are absent.

Tracheids – have a polygonal cross section, sometimes deformed by compression. In the early-wood, they have the radial / tangential diameters of the tracheids of 20-35 (60) / 17-30 (45) μm and are not too thick walled, having 3-6 μm (double wall); in the late wood the diameters are between 8-15 / 4-15 μm (r/tg d.) and the wall thickness reach 7-10 μm (double wall). The cells are regularly arranged in 2-9 radial rows between two successive rays, and intercellular spaces are often present. The density is between 1200-1700 tracheids per mm 2. Tracheid length difficult to measure, and sometimes, at cross fields meeting, the tracheids are bent. Radial pitting is usually uniseriate, sometimes biseriate, spaced, opposite, but often loosely arranged, partly touching each other. The pits, of bordered type, are round, with 10-18(-20) μm in diameter, with ornate chambers, apertures sometimes notched. Torus less visible. In tangential view uniseriate pits appear, small, of 9-10 μm in diameter, sometimes larger and slightly irregularly arranged. Helical thickenings absent, 87 but striations sometimes are present. Crassulae sometimes present. Often, the pits are located in a kind of nest and are slightly rounded by the tracheidal wall. Callitroid thickenings absent. Organic deposits absent.

Axial parenchyma - appear in cross section as few, dark, smaller cells and diffusely arranged, scattered or as short tangential lines. In longitudinal section the vertical string of cells shows transverse walls thin and smooth, sometimes nodular. Also, resin content is present as rare, small and big black globules or granules.

Rays - in cross section appear thin, linear and exclusively uniseriate in tangential section have sometimes some biseriate storeys, up to almost biseriate rays. The rays are of low type, having from 1-12 cells in height, sometimes more. Regarding the ray composition, the rays are homogeneous, with the parenchymal cells all procumbent, of 15-20 μm high, marginals taller, of up to 27-30 μm. Ray tracheids - absent. The horizontal and the tangential end-walls of ray parenchyma cells are smooth and simply pitted. Indentures present, but often difficult to observe. In cross field, the pits are of cupressoid or taxodioid type or with glyptostroboid aspect, in one row arranged as 1-2 pits of 8-12 μm, and more numerous, 3-5 (-6) pits, in the taller cross fields, when are in 2 superposed rows, or slightly irregularly arranged. Sometimes, globules of resin or granules are present inside the ray cells.

Resin canals – are absent.

Mineral inclusions – are not present.

Affinities and discussions

Glyptostroboxylon Conwentz emend. Dolezych & van der Burgh , but closer to the current Cunninghamia R. Br. , than to Glyptostrobus Endl. emend. Dolezych & van der Burgh, 2004

In fact, as was showed above, long time ago, Kräusel (1913: 45, 46) had already observed such affinity and difference in specimens assigned to Glyptostroboxylon , and considered as separating the fossil wood of Cunninghamia - type from that of Glyptostrobus - type, especially based on the presence of cupressoid cross-fields rather than glyptostroboid ones. Eventually, he rejected the idea and the two distinct taxa have remained united as Glyptostroboxylon tenerum Conwentz ( Kräusel 1913, 1919, 1949; Dolezych & van der Burgh, 2004). It is known that the genus Glyptostrobus Endl. was described firstly in fossil (as Glyptostrobus tener by Kraus, 1864) and only later it was found as living tree in China and described by Henry & McIntyre (1926) as Glyptostrobus pensilis (Staunton ex D. Don) K. Koch , known as “Chinese swamp cypress”, and they considered it as a living fossil.

Now, Glyptostroboxylon tenerum is interpreted as fossil wood of Cunninghamia type, because Gothan (1905) and later, Rudolph (1935), Watari (1948), Süss & Velitzelos (1997) and Fairon-Demaret et al. (2003) have also observed structural affinities between the wood of Glyptostroboxylon tenerum and the one of the extant Cunninghamia R.Br.

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Dolezych & van der Burgh (2004), after a new investigation on the original material from Wetterau, the type-locality, decided that the affinity of this wood is not to Glyptostrobus Endl. , but clearly to Cunninghamia R. Br. ,

genus belonging now to the Subfamily Cunninghamioideae (Zucc. ex Endl.) Quinn , not to Taxodioideae Endl. ex K. Koch , so that it could be subject for a new revision even if it is admitted now as species of Glyptostroboxylon (Dolezych, 2011) . We discuss below many other wood remains described as Glyptostroboxylon tenerum especially from Europe, and which are very similar to our studied material:

• Kräusel (1919) has determined from several Silesian sites, some xylites as Glyptostroboxylon tenerum and, for example, the specimen of Laasan has clear affinity to the recent Cunninghamia -wood, having in the cross-field three relatively large taxodioid and glyptostroboid pits, almost filling it (Dolezych & van der Burgh, 2004).

• Stockmans & Willière (1934) have described a Glyptostroboxylon tenerum , from the Eocene from Belgium, with affinity to Cunninghamia -wood, having uniseriate radial pitting, loosely arranged.

• Schönfeld (1952) has described a Glyptostroboxylon tenerum , on an Eocene wood from Borna lignite mining area ( Germany), also with a clear affinity to Cunninghamia , especially by the aspect of the cross-field pits.

• Kostyniuk (1967) has investigated some samples of xylite from the Cenozoic lignites of Turów ( Poland), describing a Glyptostroboxylon tenerum , with glyptostroboid and taxodioid pits in cross field, which points to the affinity to Cunninghamia wood type.

• Greguss (1967) determined a silicified wood from late Miocene of Hungary as Glyptostroboxylon No. 2, having uniseriate tracheidal pitting, suggesting affinity to Cunninghamia wood.

• Mathiesen (1970: 50-52) identified a wood from the lignite of Troldhede ( Danemark), as Glyptostroboxylon tenerum , and even if he made a slightly confusing description, the illustrations clearly suggest the affinity to the current Cunnnghamia wood.

• Ravazzi & van der Burgh (1995) described a Glyptostroboxylon tenerum , from the brown coal of Leffe palustrine deposits (Early Pleistocene, Lombardy, NItaly) as having the radial pitting of tracheids and cross field pitting which suggest clear affinity to the wood of Cunninghamia (Dolezych & van der Burgh, 2004) .

• The specimens described as Glyptostroboxylon tenerum , by Iamandei et al. (2001), from Eastern Carpathians and by Nagy et al. (2002) from South Apuseni mts. are probably wrongly identified, having glyptostroboid cross-field pits (see above).

• Fairon Demaret et al. (2003) have described an in situ Glyptostroboxylon tenerum , from the Eocene Forest of Hoegaarden ( Belgium), the wood structure showing clear affinity to the wood type of Cunninghamia .

• Süss & Velitzelos (1997, 2008) have studied some wood remains of Glyptostroboxylon - type from Lesbos, describing a new species ( Glyptostroboxylon microtracheidale Süss et Velitzelos ), as having ‘ovoid’ pits in cross-fields (i.e. glyptostroboid pits), suggesting that it is probably a root wood and specifying that it m to be similar with that of Cunninghamia lanceolata (Lamb.) Hook. , an extant Chinese species.

• Dolezych, M., (2011) identified some taxodiaceous woods in Lusatia (Central Europe), but also a Glyptostroboxylon tenerum with affinity to the wood-type of Cunninghamia . In fact, some years ago, Dolezych & Van der Burgh (2004) have studied fossil wood from Wetterau, the locus tipicus for the original material of Kraus (1864), which proved similar to the current Cunninghamia (see above)

• And, also, Dolezych et al. (2018) studying some material from high latitudes of North America (Yukon, Elsemere Island and around), have described some Cretaceous-Paleogene conifers, among them a Glyptostroboxylon tenerum with its typical xylotomy .

Thus, taking into account the above disscussion for the first species of Gyptostroboxylon and the comparative discussion for this studied material, and based on the great similarity of the xylotomical characters of this studied rich material (53 specimens), with the details comprised in the specific diagnosis and with other identifications of fossil wood presented above and also, with the xylotomy of the current correspondent (Greguss, 1955), we attribute all the studied specimens to Glyptostroboxylon tenerum (Kraus) Conwentz, 1884 . It is a perfect fossil equivalent of the actual Cunninghamia R.Br. (Dolezych, 2011) , and is confirmed, also, by the presence of other fossil plant parts frequently described in the Aegean area as Cunninghamia miocenica Ettingshausen (Velitzelos D. et al., 2014) .

Figures

Fig. 8 a-i, (graphic scale). Glyptostroboxylon tenerum (Kraus) Conwentz, 1884; (Specimen Li.483). a-c: Cross section - quite abrupt transition, distinct growth rings; large thin-walled tracheids; parenchyma few, diffuse; d-f: Tangential section - irregular uniseriate small pits on tracheids; parenchima with nodular end walls (arrow); rays exclusively uniseriate; g-i: Radial section - tracheidal pitting 1-2-seriate, opposite; rays homocellular, cells all procumbent; cross field with 1-2(-3) cupressoid pits or taxodioid (arrows), more numerous in marginal cross fields, and slightly irregular.