Prunoidoxylon, Duperon, 1976

Iamandei, Stănilă, Iamandei, Eugenia & Ursachi, Laurențiu, 2023, Late-Miocene Moldavian Petrified Forest, Acta Palaeontologica Romaniae 19 (1), pp. 61-85 : 77-79

Prunoidoxylon multiporosum Dupéron, 1976

Fig. 7 , a-i.

Material code: Pb36, Pb40 and Pb59.

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: the 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 even by the naked eye, typical for a dicot.

Macroscopic description

The growth rings are relatively wide, with quite indistinct ring-boundaries that can be guessed when a size difference appears between the latewood and earlywood pores. The vessels porosity is of diffuse-porous to semi-ring-porous type, the pores appearing in diffuse or slightly dendritic arrangement, as solitary and small radial multiples of 2-4 vessels. The solitary vessels outline is polygonal rounded and is usually of small type, even in the earlywood, having 40-70 μm in diameters, slightly diminishing in the final wood (20-30 μm) and are moderately thick-walled: 3–5 µm the simple wall. The pores are very numerous, their density is ≥ 100 vessels per square millimeter. In the longitudinal view, simple perforation plates appear and the vascular pitting appears as numerous, alternate, small-bordered pits and poorly preserved. The vessel-ray pitting difficult to observe, is quite similar, with many reduced borders to apparently simple, corresponding to the cross-field pits (described below). Tyloses are absent, and gum deposits and crystals, are usually present.

The ground tissue – is represented by fibers, fibrotracheids and parenchyma.

The fibers are relatively thin-walled and poorly preserved, probably minutely pitted, and helical thickenings and non-septate. The fibrotracheids appear paratracheal, coiling the vessels, and are small pitted.

The axial parenchyma appear diffuse, and is extremely rare or even absent.

The rays are usually 1-5-seriate, sometimes broader, up to 10-seriate, and with variable height, sometimes up to 1 mm. Ray density is 6-8 rays mm horizontal, often more. As cellular composition, the rays are heterocellular, with all cells procumbent, the marginals slightly higher. The cross-fields, poorly preserved, have numerous alternate pits, in horizontal rows arranged, poorly preserved.

Other special details such as sheath cells or tile cells, storied structures, secretory elements, intercellular canals, cambial variants or included phloem are not present.

Prismatic crystals, inside vessels, sometimes appear, probably with a secondary origin.

Affinities and discussions

The studied specimens show some xylotomical features, especially the vessels diffuse-porous arrangement, in cross-section, very specific for the Rosaceae of ”Prunoideae” type in fact from Amygdaloideae subfamily, by priority (see Potter et al., 2007) and not Spiraeroideae, as the International Botanical Congress from 2011 stated (ICN-Melbourne Code, see Wiersema et al. 2011).

For this type of wood, the genus Prunoidoxylon was erected by Dupéron (1976), studying some fossil wood from the Stampian formation of Agenais, from ”Bassin d’Aquitaine”, France, as having xylotomical features of ”Prunoideae”, describing the species Prunoidoxylon multiporosum Duperon 1976, designed as generotype, its diagnosis including the next details: Heteroxyl fossil wood showing growth rings with semi-porous aspect, with relatively small vessels (tangential diameter of 20 to 70 μm) in dendritic arrangement in latewood, and very numerous (100 to 195 pores per square millimeter), the density being greatest in earlywood. Vessel elements of short and medium length (260-460 μm.), with spiral thickenings, with simple perforations, perhaps rarely scalariform, and with small bordered pits (5-6 μm in diameter). Parenchyma is absent or extremely rare. Rays are very fine to medium broad (1 to 5 seriate), usually low and numerous, sometimes articulated, and heterogeneous. Libriform fibres are pitted with spiral thickenings.

Selmeier (1984) described from the Upper Miocene deposits of the localities Attenfeld, Egweil and Hammerbach ( Germany), some petrified woods as members of Rosaceae family, as Crataegoxylon cristalliferum and Pruninium , alongside of a salicaceous species ( Populoxylon priscum ). He considered the valid name Pruninium Platen 1908 , not Prunoidoxylon Dupéron , citing Süss (1982: 1556).

However, Wheeler & Landon (1992) described from the Late Eocene of Nebraska ( US), between some other dicotyledonous fossil woods, a Prunoidoxylon eocenicum Wheeler & Landon, in which he described helical thickenings on vessels, tangential bands of traumatic gum canals, which are restricted to the subfamiliy ”Prunoideae”, and in particular to the genus Prunus s.l. (Metcalfe and Chalk, 1950; Zhang and Baas, 1992). Our specimens do have not such details that seem to be of traumatic origin, and so, are slightly different.

More recently, Akkemik et al. (2019) – described a new species of Prunoidoxylon , within a complex flora from the Neogene of Kilyos, a coastal area in Istanbul, Turkey, which can be similar to our specimens by their large rays. However, using the identification key of Akkemik et al. (2019) and taking into account the xylotomical features observed in our specimens as the vessels arrangement, their big density, the presence of paratracheal fibrotracheids coiling the vessels, and the ray composition, even if the studied structures are rather poorly preserved, we assign them to the species Prunoidoxylon multiporosum Dupéron, 1976.

Figures

Fig. 7 - Prunoidoxylon multiporosum Duperon, 1976. Specimen Pb59; a, b, c – cross-section: aspects of growth rings, diffuse porous distribution of vessels, fine and broad rays, regular libriform fibers, relatively badly preserved; d, e, f – tangential section, crystals in vessels (d) uniseriate and multiseriate rays (e, f); g, h, i – radial section, simple perforated plates poorly preserved, small pits on paratracheal fibrotracheids (i), poorly preserved cross-fields.