Ulmoxylon scabroides Greguss, 1969

Iamandei, Stănilă, Iamandei, Eugenia & Ursachi, Laurențiu, 2023, Late-Miocene Moldavian Petrified Forest, Acta Palaeontologica Romaniae 19 (1), pp. 61-85 : 66-68

Ulmoxylon scabroides Greguss, 1969

Fig. 3 , a-i.

Material code: Pb13, Pb15, Pb16, Pb21, Pb22, Pb24, Pb29, Pb30, Pb31, Pb32, Pb33, Pb34, Pb35, Pb43, Pb46, Pb47, Pb48, Pb49, Pb54, Pb60 and Pb63.

Locality: Simila gravel quarry (Vaslui county), central part of Moldova, Northward of Bârlad.

Repository: in the Collection of the Natural Sciences Section of the Museum “Vasile Pârvan”, from Bârlad city, Romania.

Age: Maeotian age.

Formation: Fluvio-deltaic sediments with gravel levels, exploited in Simila gravel quarry, where the petrified wood samples appear as reworked centimetric elements with obvious ring porous and fibrous structure with big vessels – visible by the naked eye, typical for a dicot.

Microscopic description: The growth rings appear distinct in cross-section, defining a general structure of a ring porous wood, with distinct boundaries marked by the abrupt change of size and distribution of the vessels, large ones in the earlywood face to the latewood where they appear small and with typically ulmiform arrangement, as wavy thick bands.

Thus, the vessels are obviously two-sized, in the earlywood they are usually solitary and large-sized and in slightly irregular radial arrangement, or as small groups of 2-3, slightly deformed, appearing as 1–3 tangential rows, or more. In the latewood, they are clustered in 1-6 short tangential bands, thick of 3–6 tangential rows of smaller, unequal, crowded and deformed thin-walled pores. These bands are not always tangential, usually they are slightly diagonal between two rays, giving to the general structure a slightly wavy aspect (= the typical ulmiform arrangement). The solitary large vessels are round to oval or slightly deformed by tangential compression, having the radial/tangential lumina diameter of 150-300/50– 150 µm and moderately thick walls, of 2–3.5 µm (simple wall). The smaller pores of the latewood are usually oval or deformed by tangential compression, with lumina of 15–50 µm in diameter and with relatively thin walls of about 2–3 µm (double wall). The density is variable, for the large pores of the earlywood, of 3–5 pores on tangential millimeter, and more numerous in the latewood, of 16-24 pores on tangential millimeter, i. e. 100-450(-600) pores on square millimeters, sometimes more for they are small and crowded in the latewood. Longitudinally, simple perforation plates are present, sometimes badly preserved. The intervascular pitting, usually poorly preserved, is alternate, contiguous, numerous, polygonal rounded, bordered, of (7)9-13 µm in diameter, and have small circular apertures, rather less visible. The vessel-ray pits appear in horizontal row, have much reduced borders to apparently simple, corresponding to the ray-cell pits from the cross-fields, described below. The size of the vascular elements is difficult to measure because the simple perforations are, usually, less visible. Helical thickenings in vessel elements are not present. Sometimes inside the vessels tyloses and fungi remains can be observed.

The ground tissue is constituted of libriform fibres and parenchyma.

The axial parenchyma in cross-section appears apotracheal, diffuse in the transitional and latewood, mixed with libriforms, but also as paratracheal parenchyma, close to the earlywood vessels or close to the clusters of vessels in the latewood type. In the longitudinal sections, it is also visible as touching vessels, and it is obviously pitted, and sometimes, chambered and crystalliferous.

The libriform fibres show in cross-section roundedshaped lumina, of 10–20 µm in diameter, with moderately thick walls, of 3–5 µm, and are densely arranged especially in the earlywood.

Tracheids, vascular fibres or vasicentric tracheids are not present.

The rays are multiseriate, having a quasi-linear trajectory in cross sections and are slightly dilated at the ring boundary. Tangentially seen they appear 1–7 seriate (but frequently 4–6 seriate), are usually compact, fusiform and tall, of 10-60 cells in height. The ray-cells appear in the tangential sections as polygonal, rounded to oval and relatively thick-walled (of 3–4 µm double wall), are slightly unequal, even if the rays appear homocellular in the radial view, with ray-cells all procumbent. The ray-density is variable, of 7–10 rays on tangential millimeters, finer rays being less frequent. Radially the rays show cross-fields with vessels with small pits, of 3–4 µm, poorly preserved, even indistinct.

Mineral inclusions appear sometimes as various crystals, in the axial chambered parenchyma.

Other details. Storied structure - not present in the structure. Secretory elements – as oil or mucilage cells not present. Intercellular canals - not present. Cambial variants – as included phloem not present.

Affinities and discussions

The distribution of the vessels, in cross-section, defines a ring-porous structure with two-sized classes of vessels recognized as typical arrangement, defined as ”ulmiform”, very specific for the members of Ulmaceae family, especially for the current genus Ulmus L.

Consulting the atlas of Schweingruber (1990), the paper of Sweitzer (1971), the sites of Schoch et al. (2004 - www.woodanatomy.ch) and of Wheeler (2011 – as InsideWood - onwards - http://insidewood.lib.ncsu.edu/search) and also, the atlas of Akkemik & Yaman (2012), we found a great similitude of the structure of our specimens with the current Ulmus glabra Huds. , named „scotch elm” or „wych elm”, a taxon spread in Europe and temperate Asia, and also in the Mediterranean area (including Northern Africa and Middle East). This species includes now several synonyms, inclusively U. scabra , U. campestris … (see The Plant List - Ulmus glabra Huds. — The Plant List).

The accepted fossil correspondent genus for this wood type is Ulmoxylon Kaiser , which was described by the study of a Miocene ulmaceous wood from Gleichenberg - Steiermark, Austria. Kaiser (1879) named it Ulmoxylon , reviewing the species Cottaites lapidariorum Unger (see Jogmans & Edwards, 1931 p.80-81) and, probably considering it as a type for the genus, he did not design it, clearly, a genus-type, a fact that now is not accepted, considered ” type non designatus” (see ING Database).

In fact, more recently, Doweld (2017) made a proposal to reject the name Cottaites , specifying that ”at the present time, Ulmoxylon is widely adopted in modern palaeobotany for ulmaceous fossil woods, containing nearly 12 species” (Gregory et al. 2009, p.133); see also IFPNI (2014) - http://fossilplants.info/). Also, Doweld (2017) specifies: Ulmoxylon Kaiser should not be confused with its later illegitimate homonym Ulmoxylon E. Hofmann (1939) , which was later renamed as Celtixylon by Greguss (1943), having affinity with Celtidaceae Endl. (see Endlicher 1841, p.163-164).

We remarked Kłusek (2012), who made a good discussion on the adventures of the genus name for ulmaceous fossil wood, classified, in time, as Ulminium , Ulmoxylon or Ulmus . Also, she gave a useful comparative table of the previously described fossil species.

However few European fossil species were described until the present day and we used some of them for comparison with our here studied specimens.

Starostin & Trelea (1969) described from the Moldavian area, an Ulmoxylon kersonianum from the Carpathian Miocene, quite similar to our specimens having also two-sized vessels and ulmiform arrangement in latewood.

Privé & Brousse (1969) described from western Europe an Ulmoxylon aff. lapidariorum (Unger) Felix , on poorly preserved material. Latter, Privé-Gill et al. (2008) described an Ulmoxylon lapidariorum , considered to be closer to the extant species Ulmus campestris L., and quite similar to our specimens, especially by the typical ulmiform arrangement of the latewood.

Greguss (1969) described from the Mio-Pliocene of Hungary an Ulmoxylon cf. Ulmus carpinifolia Gled. , slightly different of our specimens by their short and wide rays.

Also, Petrescu & Dragastan (1971) described from the Carpathian area an Ulmoxylon cf. Ulmus americana L., has well-developed latewood with long wavy bands of vessels as ulmiform aspect, slightly different of our specimens.

Sakala (2002), described on some fossil wood from Czech Rep. an Ulmoxylon marchesonii Biondi which has structural details similar to the current species Ulmus macrocarpa Hance , from North America, to U. parvifolia Jacq. from China and to the European common elm U. carpinifolia Gled. and, having short and wide rays, is slightly different of our specimens which have tall rays, slightly slender.

Iamandei & Iamandei (2010) described from the Miocene formations from Solești area, an Ulmoxylon scabroides as identical to the species described by Greguss (1969) from the Miocene deposits of Hungary, which corresponds to the current Ulmus scabra Mill. which is a synonym of the „scotch elm”, i.e. Ulmus glabra Huds.

Thus, by their typical ulmiform ring-porous structure, with two-sized vessels, 1-3 rows of big vessels in the earlywood, simple perforations and alternate pitting on vessels, apotracheal and paratracheal parenchyma, sometimes chambered and with crystals, 1–7 seriate rays, but frequently 4–6 seriate, are usually compact, fusiform and tall, of 10-60 cells in height, homocelular and with typical pitting in the cross-fields, structural features similar up to identity with the current „scotch elm” and with the fossil species described by Greguss, we attribute the studied specimen to the fossil morphospecies Ulmoxylon scabroides Greguss, 1969 .

Figures

Fig. 3 - Ulmoxylon scabroides Greguss, 1969. Specimen Pb49. a, b, c – cross-section: ring porous structure with two-sized vessels, small vessels in late wood grouped in ulmiform arrangement; d, e, f – tangential section: fusiform broad rays, vessels, ground mass; g, h, i – radial section: vessels with simple perforations, homocellular rays, pitted ray cells in cross fields.