Taxodioxylon HARTIG emend. GOTHAN

Koutecký, Vít & Sakala, Jakub, 2015, New Fossil Woods From The Paleogene Of Doupovské Hory And České Středohoří Mts. (Bohemian Massif, Czech Republic), Acta Musei Nationalis Pragae Series B 71 (3 - 4), pp. 377-398 : 379-380

Taxodioxylon HARTIG emend. GOTHAN Taxodioxylon gypsaceum (GÖPPERT) KRÄUSEL (stem wood)

Pl. 2, Fig. 1–5, Text-fig. 5

1971 Taxodioxylon gypsaceum (GÖPPERT) KRÄUSEL ; Prakash et al., pl. 30–31, fig. 1–9.

1972 Taxodioxylon gypsaceum (GÖPPERT) KRÄUSEL ; Selmeier, p. 123–126, pl. 1–4.

1996 Taxodioxylon gypsaceum (GÖPPERT) KRÄUSEL ; Van der Burgh and Meijer, p. 374, fig. 1a–g.

2008 Taxodioxylon gypsaceum (GÖPPERT) KRÄUSEL ; Teodoridis and Sakala, p. 300, fig. 5.1–5.5.

2011 Taxodioxylon gypsaceum (GÖPPERT) KRÄUSEL ; Dolezych, p. 28, fig. 5–6, p. 29, pl. 1/1–2.

M a t e r i a l: Bečov 2 and 44804.

D e s c r i p t i o n. Growth rings distinct, 0.1–1.2 mm wide, with earlywood zone distinctly wider than latewood; transition from earlywood to latewood is gradual.

Tracheids: Outline polygonal to hexagonal. Radial diameter of earlywood tracheids 21–38–56 µm, wall thickness 3–6 µm; radial diameter of latewood tracheids 7–19–28 µm, wall thickness 3–7 µm; tangential diameter of tracheids ranges from 14 to 49 µm; number of tracheids between two rays ranges from 1 to 8, most frequently 4 (Tab. 2). Pitting in radial tracheid walls uniseriate to biseriate; bordered pits circular in outline, 12–17 µm in diameter, with crassulae present ( Text-fig. 5 ).

Rays: Mostly uniseriate, occasionally biseriate, with very low average height (4 cells). Total range of height between 1 and 16 cells (Text-fig. 4); 6–8 rays per tangential mm and 42–86 rays per square mm tangentially. Individual ray cells 15–21 µm high, horizontal and end walls thin and smooth (3–6 µm). Ray tracheids absent. Cross-fields pits cupressoid to taxodioid, 7–12 µm in diameter, 1–4 pits per cross-field, arranged mainly in one horizontal row, in two rows in marginal parts.

Axial parenchyma: Diffuse. Transverse walls thin (ca 2 µm) and smooth, but in sample Bečov 2, there are probably some nodular thickenings.

D i s c u s s i o n. This wood, similarly to the previous wood type, shows typical features of Cupressaceae : axial parenchyma present, cupressoid to taxodioid cross-field pits, with both resin canals and spiral thickenings on tracheids absent. The bordered pits in radial walls of the tracheids are disposed in two continuous vertical rows; the presence of taxodioid pits in cross-field, and predominantly smooth horizontal and end walls of the ray parenchyma point this wood to the genus Taxodioxylon ( Süss and Velitzelos 1997) . More than three pits in the cross-field, and mostly smooth walls of the ray parenchyma are typical of T. gypsaceum ( Kräusel 1949) . Van der Burgh (1973) recognizes very thin walls of the ray parenchyma as an important feature, which differentiates T. gypsaceum from other species of Taxodioxylon , but in a later study by Van der Burgh and Meijer (1996), those authors discussed variability in this species, including wall thickness.

T. gypsaceum is described from the Doupovské hory and České středohoří Mts. by Prakash et al. (1971); from the Most Basin by Teodoridis and Sakala (2008); from Germany by Selmeier (1972), Gottwald (1992), Van der Burgh and Meijer (1996), Dolezych (2011); and from numerous additional European Tertiary sites.

As stated above, the intra-specific and individual variation in T. gypsaceum ( Van der Burgh and Meijer 1996) is quite important.

Such variation is also evident in modern wood studies, e.g. Sequoia sempervirens ( Bailey and Faull 1934) , Abies balsamea ( Falcon-Lang 2005) and Larix decidua ( Denne and Gasson 2008) , which all show relatively high variation of anatomical features in conifer wood, both individual and intraspecific. It therefore seems probable that some taxa were defined superfluously in the past (e.g., see discussion in Van der Burgh and Meijer 1996) on the basis of these variations, although they may well have belonged to the same species, and their differences only reflected differing habitats or parts of the same plant. Van der Burgh and Meijer (1996) point to similarity of T. gypsaceum and some others taxodiaceous wood, like T. albertense , and suggest that possibility they all belonged to the same botanical species.

Another similar species, which was described by Teodoridis and Sakala (2008) from the Tertiary Most Basin, is T. taxodii GOTHAN. Several authors (e.g., Gottwald 1992, Teodoridis and Sakala 2008 or Dolezych 2011) describe thin walls of the ray parenchyma cells for this species, similarly to T. gypsaceum . However. T. taxodii has cross-field pits whose diameter is around half the size of those in our wood, and typical nodular thickenings on the transverse walls of the axial parenchyma ( Gottwald 1992, Teodoridis and Sakala 2008, Dolezych 2011). Similarly, our wood does not present pitted horizontal walls of the ray parenchyma, which are considered typical of this species by Kräusel (1949). As a result, we designate our wood as Taxodioxylon gypsaceum (GÖPPERT) KRÄUSEL. T. gypsaceum is generally associated with recent Sequoia sempervirens (D. DON) ENDLICHER (e.g., Selmeier 1972, Dolezych 2011) as its nearest living relative. In the Most Basin, Teodoridis and Sakala (2008) associated T. gypsaceum with Quasisequoia couttsiae HEER , on the basis of co-occurring remains of leaves or cones ( Sequoia is missing there). Absence of Sequoia remains together with parallel presence of Q. couttsiae was pointed out by Van der Burgh and Meijer (1996). In the study area, Q. couttsiae is known only from several localities where the sandstone of Staré Sedlo Fm. occurs ( Knobloch et al. 1996), and no other remains of Sequoia or Quasisequoia have been recorded.

Figures

Text-fig. 5. Schema of radial section of T. gypsaceum (sample Bečov 2). t – tracheid, r – ray, bp – bordered pit, tp – taxodioid pit, cp – cupressoid pit, c – crassulae.