Taxodioxylon taxodii Gothan, 1906

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 : 79-82

Taxodioxylon taxodii Gothan, 1906

Fig. 6 , a-i.

79 Material

Under this name were grouped 18 studied samples of silicified wood with typical taxodiaceous xylostructure. They were found either as dispersed fragments or as in situ big petrified trunks, preserved by late Oligocene to early Miocene volcano-sedimentary deposits from Aege- an area, both from continental and insular part. Thus, from Evros were collected from Lefkimi the samples numbered with these field-numbers: Lfk.70, 253, 268, 269, 270 and from Trifili - the samples Tf.108, 110, 122, 126, 127, 127a, 127b. Also, some samples were collected from early Miocene of Limnos Island, numbered with Li.189, 190, 206, 208, 210, 251. 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

The growth rings – have variable wideness in transverse section, from low to often high (8-15 cells, to over 50 cells) with quite abrupt transition from early-wood to late-wood or, sometimes, slightly gradual. The late wood is represented by few rows of smaller cells, flattened and thick walled, the growth rings boundaries are distinct, whereas usually the early wood always starts with larger and with thinner-walled cells.

The tracheids – are in polygonal cross-section, often rectangular and with rounded corners, are sometimes deformed by compression. In the early-wood, they have the radial / tangential diameters of 20-50 / 17-40 μm and wall thickness of 4-7 μm (double wall); in the transitional wood, when present, the diameters are quite similar, diminishing in size slightly gradually toward the late-wood, which is represented by (3-)5-7 rows of tracheids with smaller lumens, with diameters of 8-17 / 10-15 μm, and thick walls of 8-12 μm (double wall) in the final wood. Between two successive rays there are 2-9 radial rows of tracheids, regularly arranged. Intercellular spaces are often present. Tracheid density is (980-)1600-1716 tracheids per mm 2. However, the tracheid length is difficult to measure. The tracheid pitting on radial walls appear uniseriate or biseriate, spaced and oppositely arranged. The pits are of bordered type, round shaped, 18-21 μm in diameter, with large chambers and round and large elliptic aperture. Torus less visible. On the tangential walls pitting is usually missing, or it appears sometimes as uniseriate, smaller, round, bordered pits, of 12-15 μm in diameter, sometimes slightly irregularly arranged. Helical thickenings on tracheids are not present but, sometimes, striations can appear on the slightly bent endings. Crassulae are absent. Callitroid thickenings - absent. Organic deposits absent.

The axial parenchyma – present and appear in cross section few, in diffuse arrangement, scattered throughout the entire growth ring, as smaller cells, usually with dark content. In longitudinal sections, the string of parenchyma cells shows transverse end walls, thick of 2-5 μm, 80

nodular with up to 8 bead-like knots or even denticles, often badly preserved. Inside the cells a resin content can appear, as black globules or granules, or as plugs, or compact and with convex empty spaces.

The rays – are exclusively uniseriate, and in tangential sections appear sometimes with some biseriate storeys up to almost biseriate; they are of low to middle type (from 1-3 to 7-15 cells) or of taller type (of 16-30 cells, sometimes more). In radial section the rays are homogeneous, with parenchymal ray-cells all procumbent, of 16-20 μm tall, the marginals being usually taller (up to 24 μm), and without ray tracheids. The horizontal walls of the ray cells are thick, the double-wall has 5-8 μm, smooth and pitted (they are not ray tracheids). The tangential end-walls are thick, of 3 μm simple- wall, smooth or slightly rugose or nodular, straight or inclined or arcuated. Indentures were not observed or are missing. The cross fields have 1-2(-4) taxodioid pits, arranged in horizontally pairs or superposed in the taller cross fields. These pits are oculipores of taxodioid type, of (7-)9-12 μm, with large inclined apertures, rarely with cupressoid or glyptostroboid aspect. Globules of resin or granules are often present inside the ray-cells.

Resin canals – are absent.

Mineral inclusions – are not present.

Affinities and discussions

The synthetic xylotomical description of the 18 studied specimens, showed a characters’ combination similar to the "taxodiaceous” wood type from Cupressaceae family, namely the absence of resin canals, biseriate radial pitting on tracheids, the nodular transverse end wall of the axial parenchyma and the cross field pitting typical taxodioid, xylotomical details which characterise the current Taxodium wood-type (Fairon-Demaret et al., 2003; Dolezych and van der Burgh, 2004; Phillipe & Bamford, 2008; Dolezych, 2011; Ibrahim, 2015). Advanced genetic and morphologic studies on the members of Cupressaceae family (discussion above) allowed a better organization of them, distributed now in seven subfamilies (Gadek et al., 2000; Farjon, 2005). The former "taxodiaceus” genera are now redistributed (discussion above), and the Taxodioideae subfamily includes only three genera with disjunct living-area in North America and East Asia: Taxodium Rich. Cryptomeria D. Don. and Glyptostrobus Endl. (Gadek et al., 2000; Farjon, 2005; Schulz & Stützel 2007; Mao et al., 2012).

• Regarding the “taxodiaceous” fossil wood, we have presented above the fossil genus Taxodioxylon Hartig 1848 , whose type species T. goeppertii Hartig was considered an equivalent to Sequoia sempervirens (Gothan,1905, 1906; Philippe, 1993). However, Kräusel (1949) established the genus Taxodioxylon for taxodiaceous fossil wood, and it became a “pocket genus” for many fossil correspondents of many current members of the former “ Taxodiaceae ” family (Dolezych, 2011).

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• Greguss (1967) considered that the name Taxodioxylon should remain reserved for structures characterized by the presence of numerous nodular thickenings (up to 8) on the horizontal end-walls of the axial parenchyma, which is typical to the extant genus Taxodium .

• But Privé-Gill (1977) considered the diagnosis of the Taxodioxylon -genus as sufficiently comprehensive, therefore establishing new areas of competence for other genera could complicate the determination of fossil wood.

• A much-documented discussion on the fossil cupressaceous xylotaxa, especially on Taxodioxylon genus, is made by Dolezych (2011), who also proposed a revision of it.

• Anyway, despite some confusion inside the Taxodioxylon fossil genus concerning its modern affinities (Fairon-Demaret et al., 2003; Dolezych & van der Burgh, 2004, Phillipe & Bamford, 2008; Dolezych, 2011), the generic identification of the studied material here is correct and the described xylotomical details corespond to those described for Taxodioxylon taxodii by Gothan (1906), a fossil species often present in the coal-deposits as an important Cenozoic coal-generator tree and often identified in Europe (Zalewska,1953; Greguss, 1967; Gottwald,1966, 1992; Selmeier, 2001; Iamandei & Iamandei, 2000b, 2017; Iamandei et al., 2001b,c; 2005a; 2008b,c; 2012b; Teodoridis & Sakala, 2008; Akkemik et al., 2009; Uhl et al., 2014). It has usually 1-2-seriate pitting on the radial walls of the tracheid, nodular end-walls of the axial parenchyma and cross fields with 1-2(-4) taxodioid pits.

In a synthetic description all the here studied specimens show distinct growth rings without resin canals, tracheids with 1-2-seriate radial pits, without crassulae, diffuse parenchyma with nodular transverse end-walls (with up to 8 knots), uniseriate homogeneous rays, ray cells with nodular end-walls and cross fields with 1-2(-4) taxodioid pits, details that perfectly fit to the diagnosis of the classic species of Gothan, Taxodioxylon taxodii .

Thus, based on all the above discussions on the possible affinities and on the comparison with other descriptions of fossil wood of Taxodium - type, from Kräusel (1949) to Greguss (1967), up to Dolezych & van der Burgh (2004) and Dolezych (2011), we assign all the 18 studied specimens to the species Taxodioxylon taxodii Gothan, 1906 .

We also note the fact that Dolezych (2011) affirms that this fossil species, T. taxodii Gothan , appears to be the closest to current Taxodium mucronatum Ten., not only because of the small difference in cross fields where cupressoid pits can appear (or not), but also by the habitat type, as a coal-generating species.

Figures

Fig. 6 a-i, (graphic scale). Taxodioxylon taxodii Gothan, 1906. (Specimen Tf.122). a-c: Cross section - quite gradual transition, distinct growth rings; large tracheids; parenchyma few, diffuse; d-f: Tangential section - pitting on tracheids absent; axial parenchyma end-walls nodular (arrow); rays uniseriate; g-i: Radial section - tracheidal pitting 1-2-seriate, pairs opposite; rays homocellular, cells all procumbent; poorly preserved cross field pitting with 1-2(4) taxodioid oculipores.