MALPIGHIALES JUSS. EX BERCHT. & J. PRESL, 1820

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 : 43

? MALPIGHIALES JUSS. EX BERCHT. & J. PRESL, 1820

FIG. 20A–L

Description— Growth rings present, marked by radially narrow fibers ( Fig. 20A, B ).

Wood diffuse-porous; solitary vessels rare, 8% solitary vessels, vessels predominantly in radial multiples of 2–6 (-9) ( Fig. 20A–C ); mean tangential diameter 52 µm (SD=11), range 26–76 µm; 90–121 vessels per mm 2. Perforation plates simple and scalariform with fewer than 10 bars ( Fig. 20D–F ); intervessel pits alternate ( Fig. 20G ), horizontal diameter 6–8–10 µm. Vessel-ray parenchyma pits similar in size to intervessel pits, generally oval in outline, with reduced borders ( Fig. 20H ). Vessel elements short, <350 µm. Thin-walled tyloses abundant ( Fig. 20I ).

Fibers thin- to thick-walled, apparently non-septate, pitting not observed.

Axial parenchyma not obvious in transverse sections, but visible in longitudinal section, strands of 4–8 cells.

Rays 1–2 seriate, mostly uniseriate ( Fig. 20J, K ); average biseriate ray height 227 (SD=52) µm, 131–315 µm. Rays composed primarily of procumbent cells ( Fig. 20I, L ); 12–15 per linear mm.

Storied structure, radial canals, and oil/mucilage cells absent.

Specimen— UF 278-84892, estimated maximum diameter 10 cm.

Occurrence— Dietz Hill (UF 278).

Comments— Specimen UF 278-84892 was problematic because it was highly compressed. The longitudinal sections provided a combination of radial and tangential views, measuring the quantitative vessel features and rays per mm were affected by the compression. The tyloses made it difficult to measure vessel element lengths.

Comparison with modern and fossil woods— We searched InsideWood’s modern and fossil wood database multiple times using various combinations of features, with almost all searches including wood diffuse-porous (5p), vessels in radial multiples of four or more common (10p), perforation plates simple (13p), intervessel pits alternate and not minute (22p 24a), fibers non-septate (66p), narrow rays (searching for rays 1–3 seriate - 97p or rays uniseriate - 96p). Although scalariform perforation plates are rare, we used their presence (14p). Most searches returned Nothofagaceae Kuprian (1962) ( Fagales ), which is an unlikely match because no macro- or microfossils of this Southern Hemisphere family have ever been found in the Northern Hemisphere ( Pujana et al. 2021). Members of the Salicaceae sensu APG were also returned as well as other malpighialean families (e.g., Achariaceae Harms, 1925 ; Euphorbiaceae Juss., 1789 ; Peraceae Klotzch, 1859 ; Phyllanthaceae Martinov, 1820 ; Putranjivaceae Endl., 1841 ). Results of other searches included Elaeocarpaceae Juss. (1816, Oxalidales Bercht. and J. Presl, 1820 ). No fossil wood in the InsideWood database was a good match. In spite of reviewing the family descriptions in Metcalfe and Chalk (1950) and reviewing the literature on the aforementioned families, at this time, we are not able to assign it to family. We suggest it belongs to the Malpighiales Martius , but we cannot confirm that placement.

Populus L. (1753) and Salix L. (1753) ( Salicaceae Mirbel (1815)) are common in the compression floras of the U.S.A., although woods of those genera are rare, which is probably because they readily decay making them less likely to enter the fossil record. Initially, we thought this sample might be Populus or Salix because the transverse section of this diffuse-porous wood shows narrow and abundant vessels that are commonly in radial multiples, abundant narrow rays, and axial parenchyma looked to be rare. However, this first impression was incorrect because this wood has some scalariform perforation plates, a feature that does not occur in present-day Salix or Populus . Moreover, strands of axial parenchyma are visible in the longitudinal sections. This sample serves as a cautionary tale that generally wood identification needs to be based on microscopic examination of longitudinal sections, not just transverse section.

Figures

Figure 20. Caption on pg. 45.