Phyllocladoxylon antarcticum Gothan, 1905
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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/A43C9C00-E954-598D-AA48-937E2591DBDC |
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treatment provided by |
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scientific name |
Phyllocladoxylon antarcticum Gothan |
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Phyllocladoxylon antarcticum Gothan Figure 3A-L View Figure 3
Studied material.
MPEF-Pb 10707, 10710, 10747, 10765, 10767, 10773 and 10776.
Localities.
LU6, LU15 and LU22 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. 3A, B View Figure 3 ), latewood with ca. 3-10 rows of tracheids (Fig. 3B View Figure 3 ). Tracheids are roundish to polygonal as seen in transverse section (Fig. 3B, C View Figure 3 ). Intertracheary pitting in radial walls is abietinean, mostly uniseriate, rarely biseriate (Si= 1.03), mostly non contiguous (Cp= 11.9%), and opposite when biseriate (Fig. 3D-F View Figure 3 ). Intertracheary pits are rounded in outline; 18.3 (12.5-26.4, SD = 1.9) μm in vertical diameter (Fig. 3D-F View Figure 3 ). Tracheid tangential diameter is 33.2 (16.3-56.6, SD = 4.7) μm. Cross-fields have mostly 1, very rarely 2, mean 1.04, pits per cross-field (Fig. 3G-I View Figure 3 ). Cross-field pits are ellipsoidal with simple borders (rarely with narrow borders) and sometimes pointed; 13.0 (7.8-17.6, SD = 1.6) μm in vertical diameter (Fig. 3G-I View Figure 3 , 6C View Figure 6 ). Wall alteration (not helical thickening) of the secondary walls of tracheids is observed (Fig. 3J View Figure 3 ). Horizontal walls of ray parenchyma cells are smooth (Fig. 3G, H View Figure 3 ). Average ray height is medium, 8.2 (1-34, SD = 5.0) cells high, rays are exclusively uniseriate (Fig. 3K, L View Figure 3 ) and with a frequency of 6.5 (3-11, SD = 0.2) rays per mm.
Remarks.
Abietinean intertracheary radial pitting and cross-fields with usually one large simple pit ( Philippe and Bamford 2008) are the observed key characters, allowing confident placement of these Patagonian woods within Phyllocladoxylon . Distinct growth ring boundaries, absence of axial parenchyma and resin plugs, and predominantly uniseriate radial pitting are characteristics of the species Phyllocladoxylon antarcticum ( Gothan 1908; Pujana et al. 2014).
Specimen MPEF-Pb 10767 frequently has biseriate opposite pits (Fig. 3D View Figure 3 ), and wider (in tangential section) tracheids, similar to Protophyllocladoxylon . However, most of its pits are non-contiguous (Cp= 23.1%), the growth rings are wider, and it has one pit per cross-field, all of which are features of the species Phyllocladoxylon antarcticum . Two other specimens, MPEF-Pb 10733 and 10778, are not very well preserved and are assigned to cf. P. antarcticum because two of the main characters (intertracheary radial pitting and cross-fields) are poorly preserved and therefore barely discernible (Table 2 View Table 2 ).
Phyllocladoxylon antarcticum is the most common species in our sample of conifer woods from Laguna del Hunco. In Patagonia, it was previously recorded in the Cretaceous ( Nishida et al. 1990), Eocene ( Pujana and Ruiz 2019), and in sediments of unknown ages ( Kräusel 1924). On the Antarctic Peninsula, the fossil-species is the dominant component of the Eocene of Seymour/Marambio Island wood flora ( Torres et al. 1994; Pujana et al. 2014) and a common component of wood floras from the Late Cretaceous of James Ross Island ( Pujana et al. 2017), the Paleocene of Seymour/Marambio Island ( Pujana et al. 2015; Mirabelli et al. 2018), and the Eocene of the Fildes Peninsula of King George/25 de Mayo Island ( Torres and Lemoigne 1988; Oh et al. 2020).
Torres and Lemoigne (1988) suggested a possible relationship of P. antarcticum with the extant genera Phyllocladus Rich., Dacrydium Sol. ex G.Forst., Microcachrys Hook. Prumnopitys Phil., and Podocarpus Labill. Pujana et al. (2014) suggested affinities with several basal extant Podocarpaceae : the prumnopityoid clade (including Phyllocladus and Prumnopitys ), Microstrobos Garden and LAS Johnson, and Microcachrys ( Knopf et al. 2012); all of those taxa share with the fossils similar wood anatomy, abietinean radial pitting, and, predominantly, one large simple pit per cross-field ( Pujana et al. 2014).
Recently, a compressed branch bearing phylloclades from Laguna del Hunco was assigned to the newly described fossil-genus Huncocladus Andruchow-Colombo et al., a stem relative of Phyllocladus ( Andruchow-Colombo et al. 2019), and pollen having affinity with Microcachrys ( Barreda et al. 2020) was also reported from Laguna del Hunco. These fossils could be related to Phyllocladoxylon antarcticum , although more evidence is necessary to confirm this hypothesis. Prumnopitys andina (Poepp. ex Endl.) de Laub., the only extant species of its genus from Patagonia, and Phyllocladoxylon antarcticum share similar wood anatomy ( Pujana et al. 2017), and it is possible that the fossil-species could be related to the extant P. andina .
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