Protophyllocladoxylon francisiae Pujana, Santillana & Marenssi
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publication ID |
https://dx.doi.org/10.3897/phytokeys.156.54175 |
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persistent identifier |
https://treatment.plazi.org/id/06199D57-C350-55ED-8417-736AABFE0EDD |
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treatment provided by |
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scientific name |
Protophyllocladoxylon francisiae Pujana, Santillana & Marenssi |
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Protophyllocladoxylon francisiae Pujana, Santillana & Marenssi Figure 2A-F View Figure 2
Studied material.
MPEF-Pb 10694.
Locality.
LU2 at Laguna del Hunco (Fig. 1 View Figure 1 , Table 1 View Table 1 ), Chubut Province, Argentina.
Stratigraphic provenance.
Tufolitas Laguna del Hunco, Huitrera Formation (Ypresian, early Eocene).
Description.
Growth ring boundaries are distinct (Fig. 2A, B View Figure 2 ), latewood with 1-3 rows of tracheids (Fig. 2B View Figure 2 ). Tracheids are roundish to polygonal as seen in transverse section (Fig. 2B View Figure 2 ). Intertracheary pitting in radial walls is mixed, uni- to biseriate, predominantly uniseriate (Si = 1.25), contiguous (Cp = 88.1%), and mostly alternate, rarely opposite, when biseriate (Fig. 2C, D View Figure 2 ). Intertracheary pits are hexagonal to rounded in outline; 19.2 (13.8-24.6, SD = 1.9) μm in vertical diameter (Fig. 2C, D View Figure 2 ). Tracheid tangential diameter is 44.5 (30.3-61.2, SD = 7.0) μm. Cross-fields have 1-4, mean 1.9, pits per cross-field (Fig. 2E, F View Figure 2 ). Cross-field pits are circular with simple borders (rarely with narrow borders); 14.8 (11.8-18.4, SD = 1.8) μm in vertical diameter (Figs 2E, F View Figure 2 , 6A View Figure 6 ). Horizontal walls of ray parenchyma cells are smooth (Fig. 2E View Figure 2 ). Wall alteration (not helical thickening) of the secondary walls of tracheids is observed (Fig. 2G View Figure 2 ). Average ray height is medium, 5.6 (1-13, SD = 3.2) cells high, rays are exclusively uniseriate (Fig. 2H, I View Figure 2 ) and with a frequency of 3.5 (2-5, SD = 0.9) rays per mm.
Remarks.
This specimen is characterized by its distinct growth ring boundaries, uni- to biseriate mixed intertracheary radial pitting, cross-fields usually with one or two mostly simple pits, relatively wide tracheids, uniseriate rays, and absence of resin-plugs and axial parenchyma. These characters indicate that this wood belongs to the fossil-genus Protophyllocladoxylon , because of the mixed radial pitting, simple large pits in the cross-fields, uniseriate rays, and smooth ray cell walls ( Philippe and Bamford 2008). Conservation of the name Protophyllocladoxylon was recently proposed by Zijlstra and Philippe (2020). Among the more than 20 species of the genus, P. francisiae is distinguished by its distinct growth ring boundaries, uni- to biseriate and mixed radial pitting, and absence of axial parenchyma and resin plugs ( Zhang et al. 2010; Pujana et al. 2014).
Protophyllocladoxylon francisiae was first described by Pujana et al. (2014) from material collected from the Eocene La Meseta Formation, Seymour/Marambio Island, Antarctica, and it was later reported from the Paleocene Cross Valley and Sobral formations that crop out on the same island ( Pujana et al. 2015; Mirabelli et al. 2018). It is also present in the Eocene-Oligocene Río Turbio Formation, Santa Cruz Province, southern Patagonia ( Pujana and Ruiz 2019). Interestingly, as is the case at Laguna del Hunco, this species is always a minor component of its floras and never dominates the assemblages.
The fossil-genus Protophyllocladoxylon is quite controversial. Vajda et al. (2016) suggested that Protophyllocladoxylon represents various unrelated botanical groups, principally because of its long temporal range from the Paleozoic to the Cenozoic ( Zhang et al. 2010; see also Andruchow-Colombo et al. 2019). Pujana and Ruiz (2019) suggested that P. francisiae , in particular, could represent an extinct member of the Podocarpaceae because it has the general wood anatomy of the family but does not conform to any of the extant genera.
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