Spiroplatanoxylon densiradiatum (Petrescu) Süss 2007

Iamandei, Stanila, Iamandei, Eugenia & Todea, Petru, 2020, Palaeoxylotomical Study Of A New Collection From Zarand Miocene Petrified Forest, South Apuseni Mts., Acta Palaeontologica Romaniae 16 (1), pp. 19-34 : 25-28

Spiroplatanoxylon densiradiatum (Petrescu) Süss 2007

Fig. 4 , a-i; Fig. 5 , a-i.

Material

From two samples of petrified wood collected from South Apuseni mts., Ociu area, Bisericii Book , from Mid-Miocene deposits (Late Badenian-Early Sarmatian), kept within “ Todea Collection ”, in Crișcior- Brad locality, under the indicative OB-2 and OB-6 , with standard oriented thin sections that were submitted to the paleoxylotomical study.

Microscopical description

The growth rings are distinct, the wood structure is diffuse-porous to slightly semi-ring-porous and the rays are dilated at ring boundaries.

The vessels appear, in cross-section, as solitary pores or as tangential to diagonal pairs, sometimes slightly angular, rounded or deformed and moderately thick-walled, 7- 10 μm the double wall. The woody bundles, between two rays, may have 1-5 vessels, which are mean sized, with the radial/tangential diameters ratio 30-63/15-35 μm The pores’ size is relatively uniform 275-360 per square mm, we can talk about a diffuse-porous wood tending to semi-ring-porous, since a gradually diminishing size is observed to the late-wood, where smaller sized pores are visible, of 15-30/12-15 μm the diameters ratio (r/tg). In longitudinal sections scalariform perforations can be seen, on tilted plates, with 12-18 or more thin bars, quite badly preserved. The vessels’ walls are bordered pitted, with opposite, horizontaly elongate pits to scalariform, by apertures’ coalescence. Even if badly preserved, helical thickenings are present, no tyloses inside the vessels appear, and the vessels’ elements length is of 80-200 μm, or difficult to measure.

The axial parenchyma is of apotracheal type, diffuse, as scattered cells among the fibers or as uniseriate short lines and as marginal (terminal) parenchyma. In longitudinal view, the parenchyma cells are thin-walled, probably simple pitted, and have strands of rectangular chambered cells, empty or bearing prismatic crystals.

The rays, in cross section seen, have linear trajectory, rectangular cells, are two-sized, of 1-4, respectively, (6)8- 12 cells wide, and have typical platanoid dilations at ring boundaries. In tangential view they appear fusiform and compact, sometimes have cell-sheath and are usually high. The body ray-cells are slightly polygonal, unequally sized and relatively thick-walled. The uniseriate ray endings have 1-5 slightly polygonal cells, often slightly larger. The ray-frequency is of 9-12 rays per tangential mm. Radially seen, the rays appear heterocellular, with procumbent body cells, the marginals square or slightly taller. Sometimes hypertrophied cells appear, most probably secretory and/or bearing crystals.

The fibres, polygonal in cross section, have rounded lumina, and are quite thick-walled (up to 3-5 μm double wall). The longitudinal walls are pitted, but quite badly preserved.

Affinities and discussions

All the observed microscopical features in the studied specimens showed in cross-section a diffuse-porous to semi-ring-porous vessels’ distribution, opposite bordered pits, horizontaly elongate to scalariform by apertures’ coalescence on vessels, spiral thickenings and scalariform perforations, and heterocellular rays dilated at ring boundary (typical “platanoid dilatations”), so, we appreciated that there are clear similarity with the platanaceous structure. The Platanaceae is a monogeneric family of flowering plants, from the order Proteales . Platanus is a large deciduous tree adapted to temperate climate and has 10-12 species and some hybrids, scattered in North America, Southeast Europe, Southern and Eastern Asia.

Its secondary xylem has moderately small vessels in radial small groups, having scalariform and simple perforations, intervascular bordered pits elongate to scalariform parenchyma apotracheal, two-sized rays with typical platanoid dilation at the ring boundary ( Greguss, 1959; Watson & Dallwitz, 1992)

As it is known, there are three still valid fossil genera of platanaceous woods: Plataninium , Platanoxylon and Spiroplatanoxylon . Extended discussions concerning the validity of these genera and of their associated species are already published ( Süss, 2007; Sakala et al., 2010; Gryc & Sakala, 2010; Továrková et al., 2011; Koutecky & Sakala, 2015; Iamandei et al., 2020, in this Journal).

• The genus name Plataninium is still used by some American, Asiatic and even European scientists, and is considered as a primitive type which support the Bayley concept regarding the xylotomic features’ evolution (see Wheeler & Baas, 1991) since it has scalariform perforations, spiral thickenings, marked heterocellular rays. Many scientists have described species under this genus name (see Felix, 1894; Brett, 1972; Crawley, 1989; Poole et al., 2002; Meijer, 2000; Page, 1968; Stockmans, 1936; Wheeler, McClammer & LaPasha, 1995; Takahashi & Suzuki, 2003).

• The genus Platanoxylon Andreánszky, 1951 was also subject of revision and dispute at least in the last time ( Süss 1960, 1971, 1986, 2007; Süss & Müller-Stoll, 1977). This genus is considered by Selmeier (1996) as representing an evolved type which has simple (and scalariform) perforations, no spiral thickenings and homocellular rays, and was longtime admitted as the best equivalent of the extant platanoid taxa ( Süss, 1960, 1971, 1980, 1986, 2007; Süss & Müller-Stoll, 1977).

• The genus name Spiroplatanoxylon Süss, 2007 was created from the Tertiary of Europe and southwestern Asia and is characterized, beside the Platanus -like wood structure, by two aspects considered more primitive but characteristic to the genus: the scalariform perforation plates and the helical thickenings on vessels. From this reason a lot of species of Plataninium and Platanoxylon were attributed to Spiroplatanoxylon (see Süss, 2007; Gryc & Sakala, 2010). Also, Icacinoxylon was reconsidered as bad identification of a taxon with only intertropical extant correspondents and the numerous species described in Europe, but not only, were reassigned to Spiroplatanoxylon ( Süss, 2007) .

In a recent paper on some wood remains from Bozovici, an extended discussion on the evolution of the taxonomy of the fossil platanaceous structures is done ( Iamandei et al., 2020, in this Journal). All the described xylotomical features of the studied specimens are consistent with the genus diagnosis of Spiroplatanoxylon , and for this reason we will attribute our woods to it.

Since the wood structure of here studied specimens from South Apuseni mts., from Ociu locality, on Church Brook, xylotomically resembles to many already described species, for example to the forms described, by Petrescu & Dragastan (1972) as Spiroplatanoxylon grambastfessardi (Petrescu) Iamandei (in Iamandei et al., 2020, in this Journal), from the Oligocene of Telega and, also, by Petrescu & Nuţu (1970, 1971, 1972) from Prăvăleni, respectively from Almaşul Mare and Boiu, as to Spiroplatanoxylon porosum (Felix) Süss, 2007 and also with the species Spiroplatanoxylon densiradiatum (Petrescu) Süss, 2007 (former Icacinoxylon densiradiatum Petrescu, 1978 ) which is almost identical, having smaller angular vessels, solitary or in clusters, scalariform perforation plates with 20-35 bars, spiral thickenings and ray cells with crystals, two-sized rays and high ray-frequency.

We tried to find very specific details, to discriminate between the described species, and to identify the studied material, which is quite badly preserved, but showing distinct growth rings, diffuse-porous wood structure to slightly half-ring-porous, vessels solitary or in tangential to diagonal pairs, angular to rounded, thick-walled, mean-sized, scalariform perforations with 12-18 thin bars or more, bordered opposite pits, horizontally elongate to scalariform by apertures’ coalescence, helical thickenings, no tyloses; axial parenchyma apotracheal diffuse, and as marginal parenchyma, thin-walled cells in strands of rectangular chambered cells, bearing prismatic crystals; rays, two-sized (1-4 and (6)8-12 cells wide), with platanoid dilations, fusiform and compact usually high, sometimes cell-sheath, body ray-cells slightly polygonal, unequally sized, thick-walled, rays heterocellular, with procumbent body cells and marginals square or slightly taller, sometimes with hypertrophied cells probably secretory and/or bearing crystals, fibres polygonal, thick-walled, pitted. Since we appreciate a close similarity with Spiroplatanoxylon densiradiatum (Petrescu) Süss, 2007 , we assign our two studied specimens to this species.

Figures

Fig. 4 a-i (graphic scale, μm). Spiroplatanoxylon densiradiatum (Petrescu) Süss 2007, Ociu, Bisericii brook, South Apuseni, Romania, sample OB-2. a-c. (cross section) – distinct boundary of growth ring, diffuse-porous wood structure, ray dilatations at boundaries; d-f. (tangential section) – two-sized rays - fine and multiseriate fusiform, spiral thickenings on vessels; g-i. (radial section) – procumbent body ray cells, chambered crystalliferous parenchyma, scalariform perforation plates.

Fig. 5 a-i (graphic scale, μm). Spiroplatanoxylon densiradiatum (Petrescu) Süss 2007, Ociu, Bisericii brook, South Apuseni, Romania, sample OB-6. a-c. (cross section) – distinct boundary of growth ring, diffuse-porous wood structure, two-sized rays with dilations at boundaries; d-f. (tangential section) – two-sized rays - fine and multiseriate; g-i. (radial section) – heterocellular ray, scalariform pitting on vessels, chambered crystalliferous parenchyma.