Piceoxylon piceae Roessler, 1937

Kłusek, Marzena, 2014, Miocene coniferous woods of the Polish Carpathian Foredeep, Acta Palaeontologica Polonica 59 (3), pp. 697-708 : 698-700

Piceoxylon piceae Roessler, 1937

Fig. 3A–F .

1913 Picea sp. ; Kraeusel 1913: 29. 1920 Piceoxylon sp. ; Kraeusel 1920: 437, pl. 28: 4–6; pl. 36: 1–4.

diamicton (Middle Miocene)

0

1932 Picea sp. ; Slijper 1932: 21.

1937 Piceoxylon piceae Roessler, 1937 ; Roessler 1937: 82, pl. 3: 10; pl. 4: 11–12.

Material.— Six specimens from Tarnów-Gumniska, marked as MZ LXVa–d, MZ LVIII, MZ LXXI. Wood is silicified, white or black, 15–25 cm long. Description is based on specimen MZ LXVa ( Fig. 3A–F ) .

Description.—The wood corresponds to fragments of trunks of at least 15 cm in diameter. Growth rings are distinct, the transition from early- to latewood is gradual. The vertical resin canals have thick-walled epithelial cells. The resin ducts are commonly paired ( Fig. 3A ). The axial parenchyma is absent.

The pitting on radial walls of tracheids is uniseriate and pits are loosely spaced ( Fig. 3C ). Bordered pits are circular and they measure 13–17 μm in diameter. Pit apertures are circular or elliptical and obliquely oriented. Tangential walls of tracheids have circular bordered pits (6.5–8.5 μm in diameter). These pits are arranged in a single irregular, scattered row ( Fig. 3D ). Pit apertures have slit-like or elliptical shape and they are obliquely oriented. Distinct spiral thickenings are confined to latewood tracheids ( Fig. 3E ).

Rays are uniseriate or partially biseriate, they have 3–20 cells in height. Some rays have resin canals ( Fig. 3F ). Horizontal resin ducts are usually located in the central part of the ray. Transverse and tangential walls of rays are thick and well pitted. Ray parenchyma cells show 2–6 piceoid pits (7–9 μm diameter) in each cross-field. These pits are circular and possess slit-like or elliptic apertures. Cross-field pits are usually grouped in two rows ( Fig. 3B ). Marginal ray tracheids have no spiral thickenings.

One of the specimens from the Tarnów-Gumniska locality ( MZ LXVd) has the characteristic features of reaction wood. Reaction wood in conifers reveals thick-walled, rounded tracheids, an increased angle of microfibrils and of spiral thickenings, distorted tips and short length of cells ( Scurfield 1973; Schweingruber 1996). All these anatomical features were observed in the analysed specimen.

Remarks.—The wood is characterised by the presence of axial and radial resin canals with thick-walled epithelial cells, the existence of well marked pits on the transverse wall of ray cells and the appearance of loosely spaced pitting on radial and tangential walls of tracheids. Moreover wood possesses spiral thickenings of longitudinal tracheids and ray tracheids without thickenings. All these features indicate that the analysed woods belong to the genus Piceoxylon Gothan, 1905 ( Philippe and Bamford 2008). This taxon consists of the contemporary wood of Larix Miller, 1754 , Picea D. Don ex Loudon, 1838 and Pseudotsuga Carriere, 1867 ( Greguss 1967).

Because of the presence of spiral thickenings confined to latewood cells, classification to the genus Pseudotsuga can be ruled out. However, identification of the analysed specimens as larch or spruce is quite a difficult task. The most reliable anatomical feature which allows these genera to be distinguished is the relative proportion of pit types in the ray tracheids. Ray tracheids of spruce usually have thick pit borders with angular extensions into the cell lumen and small pit apertures, while smooth pit borders and large pit apertures of ray tracheids are the characteristic of larch ( Bartholin 1979; Anagnost et al. 1994). The state of preservation of the analysed wood, however, did not allow the types of pit in the ray tracheids to be established. Therefore, to determine the taxonomic affiliation of the specimens, other observed anatomical features were used: gradual transition between the earlywood and latewood zone, uniseriate pits on radial walls of tracheids, and transverse resin ducts usually located in the central part of the rays. These are typical features of spruce wood ( Jagels et al. 2001; Blokhina and Afonin 2009). Comparison with the fossil wood taxa allows the analysed specimens to be classified as the species Piceoxylon piceae Roessler, 1937 . The diagnosis of Piceoxylon piceae species was formed on the basis of Pliocene wood from Gleichenberg, Austria ( Roessler 1937). Its nearest living relative is Norway spruce ( Picea abies [Linnaeus, 1753] Karsten, 1881) ( Roessler 1937).

Stratigraphic and geographic range.— Tertiary; Europe.

Figures

Fig. 3. Microphotographs of fossil wood Piceoxylon piceae Roessler, 1937 from Tarnów-Gumniska, Middle Miocene; specimen MZ LXVa. A. Vertical resin canals within reaction wood (TS). B. Crossfield pitting (RLS). C. Pitting on radial walls of tracheids (RLS). D. Bordered pits on tangential walls of tracheids (TLS). E. Latewood tracheids with spiral thickening (TLS). F. Uniseriate rays and rays with resin canals (TLS). Scale bars 50 μm.