Cupressinoxylon sp. 2

Pujana, Roberto R., Wilf, Peter & Gandolfo, Maria A., 2020, Conifer wood assemblage dominated by Podocarpaceae, early Eocene of Laguna del Hunco, central Argentinean Patagonia, PhytoKeys 156, pp. 81-102 : 81

cf. Cupressinoxylon sp. 2 Figure 5A-I

Studied material.

MPEF-Pb 10778.

Locality.

LU23 at Laguna del Hunco (Fig. 1 , Table 1 ), Chubut Province, Argentina.

Stratigraphic provenance.

Tufolitas Laguna del Hunco, Huitrera Formation (Ypresian, early Eocene).

Description.

Growth ring boundaries are distinct (Fig. 5A, B ), with a gradual transition from earlywood to latewood (Fig. 5B ). Tracheids are mostly polygonal as seen in transverse section (Fig. 5B ). Intertracheary pitting in radial walls is abietinean, uni- to biseriate, predominantly uniseriate (Si = 1.06), non-contiguous (Cp = 6.3%), and opposite when biseriate (Fig. 5C-E ). Intertracheary pits are mostly rounded in outline; 18.4 (14.9-23.9, SD = 2.2) μm in vertical diameter (Fig. 5C-E ). Tracheid tangential diameter is 32.7 (18.7-46.1, SD = 7.1) μm. Cross-fields have 1-2, mostly one, mean 1.1, pits per cross-field (Fig. 5F-H ). Cross-field pits are circular and bordered, apparently the border is usually wider than the aperture, and the aperture is rounded; 11.7 (7.7-13.7, SD = 1.8) μm in vertical diameter (Fig. 4F-H , 6D ). Horizontal walls of ray parenchyma cells are smooth (Fig. 4F-H ). Average ray height is medium, 5.9 (2-15, SD= 3.1) cells high, rays are exclusively uniseriate (Fig. 5I ) and with a frequency of 6.6 (4-9, SD = 1.4) rays per mm.

Remarks.

This specimen shares with cf. Cupressinoxylon sp. 1 the abietinean intertracheary radial pitting and bordered cross-field pits, and it also conforms to Cupressinoxylon according to Philippe and Bamford (2008). Unfortunately, it is also poorly preserved and could not be assigned with confidence to Cupressinoxylon . It differs from cf. Cupressinoxylon sp. 1 because sp. 2 has larger pits and lacks axial parenchyma. It also seems to be more similar to the Podocarpaceae than to Cupressaceae because they share the number of pits per cross-field (one, rarely two). In addition, in this specimen the mean diameter of the cross-field pits exceeds 10 μm, a feature present in South American species of Prumnopitys ( Woltz et al. 1998; Vásquez Correa et al. 2010) and in other Podocarpaceae genera ( Greguss 1955) but mostly absent in Cupressaceae , which usually have smaller pits ( Greguss 1955, 1972; Roig 1992).

Figures

Figure 1. Location map and satellite images (Instituto Geografico Nacional de la Republica Argentina, upper, and Google, CNES / Airbus, below) showing the Laguna del Hunco section and sampling locations. Scale in the satellite image below (tilted) varies across the map.

Figure 4. cf. Cupressinoxylon sp. 1, MPEF-Pb 10733: A Growth rings (TS) B detail of a growth ring boundary (TS) C Detail of roundish tracheids and axial parenchyma (arrowheads) (TS) D uniseriate non contiguous intertracheary radial pits and cross-field pit (arrowhead) (SEM) E and F cross-fields with bordered pits (SEM) G axial parenchyma (arrowhead) and cross-fields with bordered pits (RLS) H uniseriate rays (TLS) I uniseriate rays (TLS). Scale bars: 5 mm (A); 500 μm (B); 100 μm (C, I); 20 μm (D, E, F, G); 200 μm (H).

Figure 5. cf. Cupressinoxylon sp. 2, MPEF-Pb 10778: A Growth rings of type B (TS) B detail of a growth ring of type B boundary (TS) C uniseriate non contiguous intertracheary radial pits D uni- and biseriate intertracheary radial pits, opposite when biseriate (arrowheads) E uniseriate non contiguous intertracheary radial pits F cross-fields with bordered pits (RLS) G and H cross-fields with bordered pits (SEM) I uniseriate rays (TLS). Scale bars: 5 mm (A); 200 μm (B, I); 50 μm (C, D, E); 20 μm (F, G, H).

Figure 6. Schematic drawing of the cross-fields: A Protophyllocladoxylon francisiae B cf. Cupressinoxylon sp. 1 C Phyllocladoxylon antarcticum D cf. Cupressinoxylon sp. 2. Scale bar: 50 μm.