Aceroxylon Hofmann, 1939

Iamandei, Stănilă & Iamandei, Eugenia, 2017, New Trees Identified In The Petrified Forest Of Middle Miocene From Zarand, Apuseni Mountains, Romania., Acta Palaeontologica Romaniae 13 (2), pp. 37-90 : 75-77

Genus Aceroxylon Hofmann, 1939

Aceroxylon palaeosaccharinum Greguss, 1943 , emend. Fig. 16 , photos a-i.

Material

From four samples of dispersed petrified wood collected from Ociu village area on the Church brook and on the slope of TeiuȘ hill (field numbers 642, 800, 801, 806), from Mid-Miocene volcano-sedimentary deposits (Late Badenian-Early Sarmatian). The centimetric sized samples representing silicified wood fragments of beige color or brownish and are kept now in GIR collection at National Geological Museum - Bucharest under the inventory numbers 26,426; 26,454; 26,455 and 26,459 (field numbers: 642; 800; 801 and 806, respectively). Under the magnifying glass fibrous structure can be seen, annual rings few distinct, vessels and medullary rays, suggesting dicotyledonate wood.

Microscopic description

The growth rings are relatively distinct, wood diffuse porous, ring boundary marked by 2-4 terminal rows of fibers and parenchyma tangentially flattened cells and by the obvious ray dilation at the ring boundaries.

The vessels in cross section appear solitary and in radial multiples of 2-3-5 pores, and sometimes as false tangential due to the overlapping of the vessel endings. They are rounded to a radial oval, and some contain dark-brown solid deposits, granular to compact. Vessel walls are moderately thick, of 5-8 μm double wall. The radial/tangential diameters for solitary pores are of 42- 84(120) / (25)40-55(84) µm. The density is 30-56(80) vessels per mm 2. The vessels have simple perforations on inclined plates. The vertical walls of the vessels show the bordered pits round, numerous, small, of 7-9 μm in diameter, alternate, touching each other or not, the apertures small, of 1-2 μm, round or horizontally oval or even point like, helical thickenings usually absent, although sometimes they can appear as fine and almost horizontal spirals. The length of the vascular elements is (190)285-420 μm. In the vascular lumen, there are large thin- walled tyloses and reddish-brown crystals or granular content up to compact or reddish-brown-matte colored.

The axial parenchyma - appears to be of apotracheal type, as few short tangential uniseriate chains, or radial, eventually in the terminal wood also, or as long bands of 2-3 cells thick, and diffuse also. Parenchyma cells appear also of paratracheal type more visible in the longitudinal sections where appears as vasicentric, of more than 8 rectangular empty cells per strand, with simple pits of 2- 3.5 μm in diameter, in 1-3 vertical rows, or as hypertrophied chambered cells with solitary crystals.

The medullary rays - in cross section are relatively linear even if can touch vessels, and show more or less obvious dilation at the boundary of the growth rings. In tangential section the rays are 1-6(8) cells thick. The uniseriates have 4-11(31) cells in height, sometimes with biseriate storeys. The ray-cells have polygonal-rounded or oval section, of ray-cells 7-10 μm in diameter and 8-16 μm in height. The thicker rays have over 1 mm in height and are made up of mixed round to oval cells vertically elongated and the last cell is short triangular, sometimes higher. Their frequency is (6)8-10 rays per tangential horizontal mm. Radially they are homocellular with tendency to heterocellular, having in ray-body all procumbent cells, of 8-12-14 μm in height, the marginals higher or upright, of 15-20-28 μm in height. The cross fields present simple, small, of 3.5-5 μm, rectangular pits slightly spaced and alternately arranged on 2-3 horizontal rows. Sometimes the ray cells have dark content with round empty spaces, probably representing crystals. Some cells seem to preserve dark gums or mucilages.

The fibers - are in regular radial rows arranged, have a polygonal section of (8)12-22 μm diameter, with relatively thick walls, of 4-5-7 μm, large polygonal rounded lumina. Vertically they have small, bordered pits, in a single vertical row arranged, slightly irregular, and helical inclined thickenings.

Affinities and discussions

The xylotomic characters presented by the studied specimens are very similar to those described and figured by Metcalfe & Chalk (1950), Greguss (1959), Schweingruber (1990) in the extant members of the former Aceraceae family, which in the more recent APG IV classification system are included in the Sapindaceae family, more specific in the Hippocastanoideae subfamily ( APG IV, 2016), within the Acer genus, which has numerous species whose living areas cover temperate regions of the northern hemisphere and tropical mountain areas.

The general xylotomic characters of the secondary wood structure of Acer are the following: diffuse-porous wood with obvious growth rings marked by some rows of flattened fibers, pores solitary, spaced or in short multiples, vertically having spiral thickenings, alternate pitting, simple perforations and scanty apotracheal parenchyma diffuse, occasionally paratracheal, rarely terminal, rays slightly dilated to the ring boundary, 1-3-5(6)-seriate, of 40-50(60) cells in height, radially of homocellular appearance, the marginal cells rarely square and with enlarged pitting (Schweingruber, 1990; Watson & Dalwitz, 1992).

The current Acer genus is quite extensive, organized in several sections exemplified below (from Watson & Dalwitz, 1992):

- Platanoidae section: Acer campestre , A. heldreichii , A. platanoides , A. pseudoplatanus , A. tataricum ;

- Goniocarpa section: A. granatense , A. hyrcanum , A. monspenssulanum , A. obtusatum , A. opalum , A. sempervirens ;

- Negundo section: A. negundo ;

- Saccharina section: A. saccharina , A. saccharum .

Xylotomicaly, as fossil correspondents two genera were errected: the first genus, Acerinium Unger (in Endlicher, 1842), described by Unger from the Miocene of Austria, based on the species Acerinium danubiale Unger (non vidi). The situation of this fossil genus is relatively uncertain, because it did not benefit of a revision even if some species were described under it.

The second correspondent genus, Aceroxylon , could also have some problems of validity. Thus, the genus Aceroxylon was proposed by Elise Hofmann (1939) as xylotomically identical with the extant Acer L. (see ING Database). The type species of Aceroxylon Hofmann, 1939 is designated Aceroxylon abbreviatus (Feistmantel) Hofmann, 1939 , species found again by Hofmann (1944) from the Oligocene phosphorites of Prambachkirchen, Austria. From the same site Hofmann (1952), described an Aceroxylon sp. , which has distinct growth ring, solitary vessels and in radial multiples of 2-5 pores, fine and thicker rays, up to 5-seriate or more and thick walled fibres.

It is good to remark that Loubière (1939) described in the same time an Aceroxylon madagascariense Loubière, 1939 from Africa, Cretacic (non vidi), without specifying it is a new genus.

Another species described by Elise Hofmann ( Aceroxylon campestre Hofmann, 1939 ) was taken in discussion by Greguss (1943) who proposed another identification Aceroxylon cf. palaeosaccharinum? (See Greguss 1943) , which is admitted as a new combination.

Aceroxylon cf. palaeosaccharinum was found again by Greguss (1969) in the Sarmatian of Fuzerkomlos ( Hungary) having also similitudes to the extant North-American species Acer saccharina , as vessels arrangement and frequency and 1-2-seriate rays, even if the fossil specimen show the uniseriates predominating. From the same site it was described also an Aceroxylon cf. abyssinica (Hochst. ex Benth.) Greguss, 1969 .

However relatively few fossil species of Tertiary Aceroxylon were described until present in the area, and Gregory et al. (2009) cite:

- Aceroxylon sp. described by Andreánszky (1955) from the European Miocene, with some additional references in Andreánszky & Sárkány (1955);

- Aceroxylon sp. described by Selmeier (1957) also from the European Miocene;

- Aceroxylon sp. cf. Acer pseudoplatanus L. and Aceroxylon sp. cf. Acer trilobatum L. were described by Andreánszky (1959) also from the European Miocene;

- Aceroxylon pennsylvanicum Prakash, 1968 described from the North American Miocene;

- Other forms of Aceraceae were described from Japan under linean name Acer : A. momijiyamense and A. watarianum , by Takahashi & Suzuki (1988), but not respecting ICBN Rules regarding the fossil wood nomenclature.

- Also, two new species from the same area of that are described by us in this paper as Aceroxylon zarandense and A. pravalense , which are slightly different of the specimens studied here.

- Under these circumstances, the comparison with the extant species seemed to us the most appropriate solution to identify the studied material. The comparative analysis of the xylotomic patterns observed in the specimens studied here indicates a great similarity regarding the vessels' distribution, their shape and size, the aspect of the parenchyma, of the fibers and of the rays, the perforations, pitting and spiral thickenings in vessels - with the extant species Acer opalus , whose area is Southern European (or Mediterranean), or with A. tataricum , the Tatarian maple, which is widespread across Eurasian areas, from Austria to Turkey and even Russian Far East and Japan, and also with A. ginnala , a species with the living area in East Asia ( China, Manchuria, Japan).

- Also similitudes appear to have with and A. saccharum and A. saccharinum , which have a North-American area marked by a temperate-warm Mediterranean climate ( Greguss, 1943; 1959). The rays of the North American Acer negundo are biseriate, those of A. obtusatum and A. saccharinum 1-2 seriate, those of A. ginnala , however, only 1, more rarely 2-seriate and with some differences in the arrangement of the vessels. These species, characterized by the 1-2-3-seriate rays, which distinguishes them from the other types, as in the absence of spiral thickenings on the vessels and points the alternate, hexagonal intervascular pitting, the presence of solitary crystals of oxalate in the parenchyma, very obvious in all the specimens studied by us and clustered here.

- The similarity with the species described by Greguss in 1943 (reprinted in 1969) is also evident, which is why we attribute the studied material to the species Aceroxylon palaeosaccharinum Greguss, 1943 , emended here, and which we consider appropriate of our studied specimens, and similar to the extant species Acer saccharinum , A. saccharum , A. opalus and A. ginnala , whose possible fossil correspondent could be.

Emended diagnosis of Aceroxylon palaeosaccharinum Greguss, 1943 emend.

( New type: inventory number: 26426 and supplementary material: 26454; 26455 and 26459 - are kept now in GIR collection at National Geological Museum - Bucharest) .

Diffuse-porous secondary wood, with relatively distinct growth rings, rays with dilation at the limit of annual rings, vessels usually solitary and radially grouped in 2-5 pores, round to oval when solitary, small (42-84 / 40-55 μm radial / tangential diameters), with thick walls (5-8 μm double wall), density of 30-80 vessels per mm 2, simple perforations, polygonal or round bordered pitting, as numerous, small alternates pits (7-9 μm) with round to horizontally-oval apertures of 1-2 μm or even point- like, spiral thickenings usually absent, vascular elements 285- 420 μm length, with large thin- walled tyloses, and colored crystals. Apotracheal parenchyma diffuse as short or long lines, sometimes few in the final wood or very few paratracheal, simply pitted and with crystals. Rays usually 1-3-seriate, rarely thicker, the uniseriates have 4- 11(31) cells in height, ray cells polygonal-rounded or oval-vertical, with biseriate storeys, the thicker rays are fusiformes with short unicellular ending. Their frequency is of 8-10 rays per tangential mm. Radially are slightly heterocellular, ray body cells all procumbent of 8-14 μm high, the marginals higher to upright (15-20 μm, up to 28 μm), with content of crystals and gums. Cross- fields with simple small pits of 3.5-5 μm, on 2-3 horizontal rows. Radial regular rows of fibers with polygonal section and wide lumen, of 12-20 μm diameter, thick walls of 5-7 μm double wall, with pitted, septed and with spiral thickenings.

Figures

Fig. 16 Aceroxylon palaeosaccharinum Greguss, 1943 emend. a - cross section: diffuse-porous to semi-ring-porous wood, solitary vessels, two sized rays, ray dilation at the ring boundary - x50; b, c - cross-section: multiseriate rays with obvious dilations at the ring boundary, solitary vessels, thick-walled fibres - x100; d - tangential section: multiseriate fusiform rays, tall - x100; e-f - tangential section: crystalliferous parenchyma, alternate vascular pitting - x200; g, h, i - radial section: simple perforations, cross-fields, chambered parenchyma with rows of crystals - x200.