Magnolioxylon kräuselii (Greguss) Van der Burgh, 1973

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 : 22-25

Magnolioxylon kräuselii (Greguss) Van der Burgh, 1973

Fig. 3 , Photos a-i.

Material

From a sample 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-1 , with standard prepared thin sections that were submitted to the paleoxylotomical study.

Microscopic description

The growth rings are not too high, with boundaries marked by some tangential rows of thin-walled cells, radially flattened (marginal parenchyma). The structure is generally diffuse-porous or slightly semi-ring-porous, since in the late-wood the pores’ size slightly diminishes. Also, at the boundary of the annual rings, the rays present typical slight dilations.

The vessels are arranged in 1-3 radial rows between two rays and are usually solitary or in radial small multiples of 2-4 vessels. The solitary pores seem to be oval in shape, usually deformed, relatively thick-walled (of 7-9 µm the double wall), sometimes touching the rays. The diameters of the solitary vessels are of 50-70 μm. The vessel density is high, of more than 200 pores on mm2. The scalariform perforations plates have up to 10-12 quite thick bars. On the longitudinal walls, spiral thickenings are present, and intravascular pitting, as numerous pits, horizontal-elliptical, opposite, to almost scalariform, especially on narrower vessels appear. Sometimes, isolate tyloses inside the vessels are visible.

The axial parenchyma appears either as marginal bands at the ring boundary, or diffuse or scanty-paratracheal, or difficult to be observed due to bad preservation.

The rays, in cross-section seen, appear as 1-2 seriate, with slight dilations at the growth ring boundary, and consist of rectangular cells radially elongated, filled with some dark material. Generally, the rays have a linear or slightly curled trajectory and sometimes touch vessels. In tangential view it is obvious that the rays are 1-2-seriate, heterogeneous, and their frequency is of 6-10 rays on tangential horizontal mm. They have 10-25 cells in height, or are even taller. In tangential-view the ray cells appear polygonal rounded and alternately arranged, sometimes slightly uneven. Radially seen, the rays show heterocellular character, the body cells are low, procumbent, and the marginals - slightly taller. In the cross-fields numerous short elongate superposed pits appear.

The fibro-tracheids have moderately-thick walls, and horizontal-elliptic pits, opposite to almost scalariform.

The fibres have also moderately thick walls but offer few details, due to bad preservation.

Affinities and discussions

Evaluating the observed xylotomical features in our studied specimen we found that some of them as scalariform perforations, scalariform pitting, biseriate rays, heterogeneous, terminal parenchyma and thick-walled fibers, which suggest similarity with members of Magnoliaceae , a large extant family comprising 7 genera and around 230 species, partially with arboreal habit, widespread in temperate to tropical areas from Eastern Asia and North America (see Watson & Dalwitz, 1992). The Plant List (2013) admits that Magnoliaceae is a family with 5 genera and 247 species.

However only three fossil genera were validly described till now, having different diagnoses:

• Liriodendroxylon Prakash, Březinová & Bůžek, 1971 , corresponding to the extant genus Liriodendron L., known as tulip tree, whose structure can be diagnosed as such: wood diffuse-porous, with small to mean-sized vessels, solitary or in multiples of two or more, having scalariform perforations plates with few bars (6-13), then angular to elliptic intervascullar pitting, opposite, in horizontal pairs or rows, terminal parenchyma, 1-5-seriate rays or broader, slightly heterogeneous, fibers with polygonal cross field, thin to thick walled and non-septate.

• Magnoliaceoxylon Wheeler, Scott & Barghoorn, 1977 , name used especially by American and Asian scientists, as morphogenus of fossil wood of Magnoliaceae , almost identical with the morphogenus Magnolioxylon created by Hofmann (1952), is characterized by numerous narrow vessels in cross-section, mostly in radial multiples, with exclusively scalariform perforation plates, with sca1ariform intervessel pitting, marginal (terminal) banded parenchyma and 1-4-seriate heterocellular rays (see Wheeler et al., 1977; Srivastava & Suzuki, 2001; Wheeler & Manchester, 2002).

• Magnolioxylon Hofmann, 1952 , corresponding to the extant genera of magnolias such as Magnolia L., Michelia L., Talauma L., has the following diagnosis: diffuse-porous wood with low growth rings, small solitary vessels or as multiples of 2-3 up to 5(7), and simple perforated plates, small to large vascular pitting. (Additionally, scalariform perforations and scalariform pitting, and even very specific ones appear - a reason to emend the genus’ diagnosis). Rays 1-4(5)-seriate, rarely broader, with slightly sinuous trajectory in cross-section, with up to 22 cells in height, heterogeneous, body cells procumbent, marginals upright. Paratracheal uniseriate and marginal (terminal) parenchyma and thick-walled fibers are present.

The xylotomical details observed in our specimen, unfortunately rather badly preserved, support the assignment to Magnolioxylon morphogenus and, even if we had not the access some older identifications of magnoliaceous fossil woods (Unger, Caspary, Lignier, Edwards, and Kruse, for example) quoted by Schönfeld (1958), we compared our studied wood structure with more recently identified forms:

- Magnolioxylon michelioides Hofmann, 1952 , the typespecies described from Prambachkirchen, Austria, has radial multiples of 3-5-7 vessels, paratracheal and terminal parenchyma, rays of two sizes - broad of 3-5 cells and uniseriates numerous which bring it closer to the extant species Michelia baviens L. It was, also, described from the Oligocene of Canada by Roy & Stewart (1971), as having similar features or almost identical. Both forms are quite similar to our material.

- Magnolioxylon scandens Schönfeld, 1958 , described from the German Late Oligocene of Niederrheinischen Bucht, shows diffuse-porous wood with thick growth rings, solitary vessels and in small radial multiples, sometimes diagonal to tangential, simple and high scalariform perforation plates (with up to 33 bars), scalariform intervascular pitting, thick-walled tracheids, round to scalariform pitted, thick-walled pitted libriform, 1-4-seriate high rays, heterocellular with 1-3(5) rows of marginal, thick-walled, upright cells (77-92 ̒ m high). Schönfeld shows that these details suggest similarities with extant species like Magnolia and Talauma , but also with some lianas like Schisandra , Kadsura . The same species was described by us from Mid-Miocene deposits of Prăvăleni, South Apuseni area ( Iamandei et al., 2004), but is not identical to here studied specimen.

- Magnolioxylon transilvanicum Nagy & Mârza, 1967 , was described also from South Apuseni area. The wood structure presents bi- and triseriate heterocellular rays, with body ray cells procumbent, and with mostly 2-4 rows of upright and/or square marginal cells, platanoid dilations at the boundary of the growth-rings, simple and scalariform perforations, elongated to scalariform pits on vessels, simple and bordered, with slit-like apertures, scanty paratracheal axial parenchyma and, also, marginal (terminal), tracheids with spiral thickenings and scalariform pits, septate and pitted fibres. The same species was subsequently identified in the same area ( Iamandei & Iamandei, 1997), having 2-3-seriate rays, idioblastic secretory cells, scalariform perforations, bordered elliptic to scalariform pitting, quite similar, of “buttonhole” type on fibro-tracheids and on fibers. Also, a Miocene Magnolioxylon cf. transilvanicum was described from Bala area, Mehedinţi County, Romania ( Iamandei et al., 2011) and recently Magnolioxylon aff. transilvanicum in Rhodopes mts. ( Iamandei et al., 2016).

- Magnolioxylon acuminatum Iamandei et Iamandei, 1997 , is another species described from Prăvăleni, close to Ociu area, from the same Mid-Miocene deposits. It is characterized by distinct growth rings, semi-ring-porous structure wits radial multiples of 2-3(7) mean-sized vessels (84/66 ̒ m), density 105-120 vessels on sq.mm., simple perforations, alternate to opposite vascular pits, vasicentric tracheids with spiral thickenings and thin-walled tyloses, apotracheal parenchyma, diffuse and marginal, heterocellular rays usually uniseriate, with 1-4 secretory cells, 1-2 pits in cross-fields thick-walled pitted fibers ( Iamandei & Iamandei, 1997).

- Magnolioxylon sp. , described by Petrescu & Nuţu (1970) also from Prăvăleni, from the same formation, has badly preserved anatomical details - solitary vessels or in 2-3 radial multiples and 1-4-seriate rays, typical generic details - but not sufficient for a specific identification.

- Magnolioxylon parenchymatosum Van der Burgh, 1973 , described from the Late Oligocene of Niederrheinischen Braunkohlenformation, presents many xylotomical similarities with the extant species Magnolia fraseri and M. sororum and, also, with the fossil species Magnolioxylon scandens described by Schönfeld (1958) from the same deposits, having small sized vessels, with scalariform perforation plates with 2-12 spaced bars, intervascular scalariform pitting, helical thickenings, and also pitted tracheids and fibers, axial parenchyma diffuse and 1-3- banded and marginal (terminal), 1-3-seriate heterocellular rays, with body-cells procumbent, and two rows of marginal upright cells, pitted.

- Magnolioxylon kräuselii (Greguss) van der Burgh 1973 , initially described by Greguss (1969) as Liquidambaroxylon, presents, besides the generic details, simple and scalariform perforations with (3)10-12 spaced thick bars, sometimes forked, pitted and crystalliferous parenchyma, 1-2-seriate rays of 10-16 cells high, heterocellular, thick to very thick-walled fibers, pitted fibro-tracheids.

Since the here studied specimen has scalariform perforations with up to 10-12 spaced thick bars, sometimes forked, pitted and crystalliferous parenchyma, 1-2-seriate heterocellular rays, of 16-17 cells high, or more, thick to very thick fibers, pitted fibro-tracheids, perfectly resembles to the morphospecies Magnolioxylon kräuselii (Greguss) Van der Burgh, 1973 , to which we attribute our studied specimen.

Figures

Fig. 3 a-i (graphic scale, μm). Magnolioxylon kräuselii (Greguss) Van der Burgh, 1973, Ociu, Bisericii brook, South Apuseni, Romania, sample OB-1. a-c. (cross section) – distinct boundary of growth ring, marked by marginal parenchyma and ray dilations; d-f. (tangential section) – spiral thickenings and scalariform pitting on vessels, biseriate heterogeneous rays; g-i. Radial section – spiral thickenings and scalariform pitting on vessels, scalariform perforation plates, pitted cross-fields.