Taxodioxylon, Hartig, 1848

Wheeler, Elisabeth A., Manchester, Steven R. & Baas, Pieter, 2023, A late Eocene wood assemblage from the Crooked River Basin, Oregon, USA, PaleoBios 40 (14), pp. 1-55 : 5

TAXODIOXYLON SP.

FIG. 3A–I

Description— Growth ring boundaries distinct ( Fig. 3A‒C ). In rings without compression woods, latewood narrow with 1–3 rows of radially narrow longitudinal tracheids. Average tangential diameter of earlywood tracheids 32 (SD=7) in UF 278-84886, 30 (SD=7) µm in UF278-84889. Intertracheary pitting occasionally biseriate ( Fig. 3G ). Transition from earlywood to latewood gradual.

Axial parenchyma abundant, diffuse and in short lines (3A, B), end walls smooth ( Fig. 3F ).

Rays homocellular, all ray parenchyma ( Fig.3G–I ),very rarely with some marginal ray cells possibly ray tracheids ( Fig. 3G ), uniseriate ( Fig. 3D–F ), rarely with a biseriate portion one cell high; cross-field pits taxodioid, 2–4 (occasionally more) per cross field ( Fig. 3I ); horizontal and end walls of ray parenchyma smooth (Fig. H). Ray height 2–7–18 cells, average 146 (SD=77) µm in UF 278–84886, 2–7–24 cells, 153 (SD=115) µm in UF 278-84889.

Specimens— UF 278-84886, UF 278-84889, estimated maximum diameters 8 cm, 16 cm.

Occurrence— Dietz Hill (UF 278).

Comments— Ring width is quite variable in UF 278- 84886. Some growth rings have compression wood, indicated by longitudinal tracheids tending to be circular in outline with thickened walls in a broad latewood zone ( Fig. 3C ).

Comparisons with extant woods— A search for the IAWA softwood features: 40p, 43p, 61e, 72p, 73p, 76p, 80r, 85p, 87p, 94p, 98p, 99p, 103p, 107p, 109a, 110a, 118a with zero mismatches yields the following Cupressaceae: Chamaecyparis pisifer (Siebold and Zucc.) Endl. (1847) , Cryptomeria japonica (Thunb. ex L.f) D. Don (1839), Cunninghamia konishii Hayata (1908) , Cunninghamia lanceolata (Lamb.) Hook. (1827) , Glyptostrobus pensilis (Staunton ex D. Don) K. Koch (1873) , Platycladus orientalis (L.) Franco (1949), and Taiwania cryptomerioides Hayata (1906) . Taxodium distichum (L.) Rich. (1810) is among many other Cupressaceae having just one mismatch with the fossil: smooth instead of irregularly thickened or beaded transverse end wall of axial parenchyma (IAWA Softwood Feature 76), which often is of variable occurrence ( Richter et al. 2004).

Comparisons with fossil woods— Taxodioxylon has long been used for fossil woods with distinct growth rings, abundant axial parenchyma, and predominantly taxodioid cross-field pits (e.g., Kraüsel 1949). Taxodioxylon's features and variability have been reviewed multiple times (e.g., van der Burgh and Meijer 1996, Dolezych 2011) and the overlap between the different species noted. It is common in the Northern Hemisphere (e.g., Elliott and Foster 2014, Akkemik and Acarca Bayam 2019) and has been used for fossil woods resembling not just Taxodium Richard (1810) , but also Cryptomeria Don (1838) and Cunninghamia R. Br. Ex Rich. (1826a) ( Yi et al. 2003, Miocene China), two of the genera returned in our search of the InsideWood conifer database. Given that this Dietz Hill wood conforms to van der Burgh and Meijer's concept of the genus, we assign it to Taxodioxylon , but not to a particular species.

Figures

Figure 3. Cupressaceae. Taxodioxylon sp. A, C, E–I. UF 278-84886. B, D. UF 278-84889. A, B. Narrow latewood zone, axial parenchyma dif- fuse and in short tangential lines, TS. C. Latewood with compression wood, TS. D, E. Uniseriate rays, TLS. F. End walls of axial parenchyma smooth, TLS. G. Circular bordered pits on radial walls of longitudinal tracheids, occasionally biseriate; most rays homocellular composed of ray parenchyma, bottom ray with top marginal row possibly composed of ray tracheids (RT) RLS. H. Ray composed of ray parenchyma, horizontal and end walls smooth, RLS. I. Taxodioid cross-field pits, RLS. Scale bars=200 µm in A, B; 100 µm in C, D, E, G; 50 µm in F, H; 20 µm in I.