Tetraclinoxylon velitzelosii Süss, 1997

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 : 73-76

Tetraclinoxylon velitzelosii Süss, 1997

Fig. 4 , a-i.

Material

11 samples from the studied material showed a similar cupressaceous xylostructure of Tetraclinis - type, marked by the round lumina of the thick-walled tracheids and were grouped under the genus Tetraclinoxylon Grambast. The samples were collected from Greece, Aegean area, from late Oligocene volcano-sedimentary deposits from Evros region: from Lefkimi – the samples with the field numbers Lfk.151, 300, 311, 312; from Sappes – the samples Spp 25, 33, 35; from Trifili – the sample Tf.132. Also, some samples come from early Miocene deposits of Limnos – the samples Li.133, 211, and of Lesbos – the sample Lsv.13b. 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 variably wide in the cross section, having sometimes over 25-30 rows of thick-walled cells with rounded lumina, with quite abrupt size-transition, sometimes gradual, to the late-wood, which is represented by 3-5(-7) rows of smaller, very thick-walled cells and radially flattened, distinctly marking the growth ring boundary. Resin canals are absent ( Fig. 4 a-c).

Tracheids – have polygonal shape with rounded corners in cross section, in the early wood showing obviously The pits have ornate chamber and round to slightly elliptic aperture. In tangential view, sometimes, uniseriate smaller pits of 12-15 μm can appear, often with irregular arrangement, or even slightly alternate. Helical thickenings not present, but striations, in longitudinal view, often appear. Crassulae rarely present. Callitroid thickenings not present. Organic deposits absent.

Axial parenchyma – appear as few cells in diffuse arrangement in cross section, scattered throughout the entire growth-ring as smaller cells, relatively thin-walled and, usually, with some dark content, as plugs, globules or granules.

In vertical view, the string of parenchyma cells shows and smooth transverse end-walls of 2-3 μm, or feebly

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nodular, with 2-3 small nodules, often difficult to observe because of the resin content.

Rays – are exclusively uniseriate and, in tangential section, show cells with round to wide-oval shape, of 20-25 μm in diameter, usually as rays of low type, mostly of 3-5 cells tall, but sometimes of even more than 25 cells. Ray density is 9-12 rays per tangential mm. In radial section the rays are of homogeneous type, with cells all procumbent and without ray-tracheids. The ray-cells have smooth horizontal walls, less pitted, of 2-5 μm thick, and the tangential walls not pitted, of 2.5 μm thick. Indentures – are not visible or absent. In cross field, 1-2(-4) cupressoid pits appear, mostly in 1-2 horizontal rows, sometimes irregularly arranged. They appear as round cupressoid pits of 10-12 μm in diameter and with oblique slit-like apertures.

Resin canals – are not present.

Mineral inclusions – are not present.

Affinities and discussions

The xylotomical characters observed in 11 studied specimens of fossil wood, indicate a structure of ‘cupressaceous’ type, and the thick- walled tracheids with round lumen in cross-section (a detail of high taxonomic value), together with other microscopic details, like the specific radial pitting, the smooth or weakly nodular horizontal wall of the axial parenchyma and the cupressoid pits in cross field suggest a similarity to the current genus Tetraclinis Mast. (Gothan, 1905; Prill, 1913; Peirce, 1937; Phillips, 1948; Kräusel, 1949; Greguss, 1955). There is the single species of this genus, Tetraclinis articulata (Vahl) Mast. , which appear as a small tree of 6-8 m tall, rarely reaching 15 m, or only with shrub habit. It occurs now as a “living fossil” in the extreme South of Spain, in Morocco, North Algeria, North Tunisia, and in Malta, also perhaps North-Eastern Libya, as endangered species or vulnerable populations (Farjon, 2005; Earle, 2020).

Previously it was considered “the single member of Callitroideae group without callitroid thickenings” (Greguss, 1955) but, in the last classification of the family Cupressaceae lato sensu, the genus Tetraclinis Mast. is a member of Cupressoideae subfamily (Gadek et al., 2000; Farjon, 2005a; Christenhusz et al., 2011), side by side with Cupressus L., Juniperus L., Xanthocyparis Farjon et Hiep , Microbiota Komarov , Platycladus Spach , Calocedrus Kurz , Chamaecyparis Spach , Fokienia Henry et Thomas , Thuja L., and Thujopsis Endl.

• The fossil genus Tetraclinoxylon was created by Grambast (1951) having T. boureaui Grambast as type-species, which was described from the Oligocene (Chatti- an) of Paris Basin, as a perfect correspondent of the current Tetraclinis Mast. (Grambast, 1962) . The original diagnosis of Tetraclinoxylon Grambast, 1951 sounds like this: «Wood showing structure of Cupressinoxylon s.s. (sensu stricto) (Gothan, 1905). Cross section of the tracheids are rounded. Cross field pits with inclined slit-like apertures. Indentures absent and there are no thickenings of the tangential wall of the ray cells. No callitroid thickenings. Average height of ray cells - less than 25 µm» (translated from French). Our studied specimens fit with this diagnosis.

• Such a fossil cupressoid wood which was described by Vallin (1966) from Portugal as Cupressinoxylon lusitanense Vallin , but having a very a similar xylotomy with the current Tetraclinis , was renamed by Süss (1997) Tetraclinoxylon lusitanense (Vallin) Süss as new combination, as having xylotomical details similar to the current Tetraclinis . Our specimens have quite similar details.

• Privé (1973) described T. vulcanense from the Pliocene of Puy-de-Dôme, France, with xylotomy, also very similar to the current Tetraclinis . Sakala (2003), identified a T. vulcanense by the study of a big petrified late Eocene trunk from Kučlín, Czech Rep., initially wrongly determined by Březinová et al. (1994) as Podocarpoxylon helmstedtianum Gottwald, 1966 . Some similarities with our specimens were observed.

• A Mediterranean fossil species from Miocene deposits from northern Sardinia – Tetraclinoxylon anglonae Biondi – was described by Biondi (1979), having, also, many similarities to the current Tetraclinis , and also with our studied material.

• Desplats (1983), studying a Cretaceous (Albian) fossil wood collected from Pas-de-Calais area, described a new species as Tetraclinoxylon amedroi , having xylotomical details similar to the current Tetraclinis .

• Süss, 1997 has described Tetraclinoxylon velitzelosii , as a new Mediterranean fossil species, from the early Miocene of Lesbos, with xylotomy similar to the current Tetraclinis : tracheids pitting 1-2 seriate, axial parenchyma with nodular horizontal walls, relatively high rays with cupressoid cross-fields. Very similar details we observed in our studied specimens.

• The study of numerous specimens from the Carpathian area revealed another Cenzoic species was described as Tetraclinoxylon romanicum Iamandei et Iamandei, 2000 , as presenting minor xylotomical differences considered as representing intraspecific variability (like the variable frequency of the crassulae); they were assigned to the same species (Iamandei & Iamandei, 2000b; Iamandei et al., 2005b; 2008a,b; 2011). The here studied specimens present some similarities with this carpathian species.

Also, we cite here Sakala (2011, pers. comm.), who observed such variability on slides prepared from wood of living Tetraclinis articulata (Vahl) Mast. (No. 2280, UPMC, Paris): “very often 3-4 typically cupressoid pits per field appear, mostly in marginal ray cells; very rare biseriate portions of pitting on radial tracheid walls and crassulae are present especially on the wider tracheids of early wood, but no biseriate portion in rays were observed”, thus completing the descriptions found in Kräu-

75 sel (1949), Grambast (1951), Greguss (1955), Vaudois & Privé (1971), Privé (1973).

Thus, we observed in our specimens that have gradual transition from the early wood to the late-wood, sometimes quite abrupt in cross section, and the polygonal-rounded tracheids have thick to very thick walls, with round or rounded lumina. Also, uniseriate to biseriate and opposite radial pits, sometimes slightly irregular, often separated by crassulae. Axial parenchyma is present, few, in diffuse arrangement, with smooth and thin transverse end-walls, rarely feebly nodular. The rays are usually uniseriate, of low to medium type, mostly of 3-5 cells tall, but sometimes up to 25 cells or more, with lateral intercellular spaces and cross fields with 1-2(-4) cupressoid pits.

Since the description of the studied specimens perfectly agree with that of the species diagnosis of Süss (1997), a species created on fossil wood collected from the same area, the Lesbos Island, we decided to attribute them to the species Tetraclinoxylon velitzelosii Süss, 1997 .

The current corespondent has presently a very restricted Mediterranean distribution, but we must imagine that this genus had a more extended Cenozoic area in Europe, around the Paratethys Sea, indicating, for that span of time, a subtropical to warm-temperate paleoclimate of Mediterranean type. Otherwise, by the study of the Oligocene-Miocene leaf imprints found throughout Europe, a Tetraclinis salicornioides (Unger) Kvaček was described, that perfectly corresponds to the present-day species (Stancu & Ţicleanu, 1975; Kvaček et al., 1989; Givulescu, 1997; Kvaček & Hably, 1998), as well as in North America ( Kvaček et al., 2000). However, Kvaček (2002) quote the existence of a fossil subxerophytic form, identified as Tetraclinis brachyodon (Brongniart) Mai & Walther , as humid subtropical element coming from Mid-Eocene to Pliocene, in all Europe, probably from Caucasus up to Italy or to Germany - where it was first described. Kovar-Eder & Kvaček (1995) cited it from Croatia, and Givulescu (1997) cited it from Transylvania. These two fossil species coexisted, and it is very possible that this subxerophytic form have had a special wood structure, still unknown up to this day. Further studies may add better arguments to such a hypothesis. The “whole plant” principle (Sakala, 2004) could be helpful.

Figures

Fig. 4 a-i. (graphic scale). Tetraclinoxylon velitzelosii Süss, 1997. (Specimen Tf.132). a-c: Cross section - quite abrupt transition, distinct growth rings; tracheids with typicaly round lumina (arrow); parenchyma few; d-f: Tangential section - pitting on tracheids absent; parenchyma with dark remains; low rays (arrow); g-i: Radial section - stiations on tracheids (arrow) and pitting 1(2)-seriate, opposite or irregular; poorly preserved cross fields (arrow).