Pahudioxylon cf. bankurensis, Chowdhury, Ghosh & Kazmi

Gentis, Nicolas, Licht, Alexis, Boura, Anaïs, Aung, Dario De Franceschi Zaw Win Day Wa & Dupont-Nivet, Guillaume, 2022, Fossil wood from the lower Miocene of Myanmar (Natma Formation): palaeoenvironmental and biogeographic implications, Geodiversitas 44 (28), pp. 853-909 : 870

Pahudioxylon cf. bankurensis

( Fig. 9 )

Same synonymy list as Pahudioxylon bankurensis .

ORIGINAL HOLOTYPE. — Geological Survey of India ( G.S.I.) no. P2 /126.

MATERIAL. — MNHN.F.50184 (field number: 17FN06) , MNHN.F.50185 (field number: 17FN16) , MNHN.F.50186 (field number: 17FN18). Estimated minimal diameter: 10-28 cm, 38-60 cm for specimen 17FN18.

AGE. — Upper lower to lowermost middle Miocene.

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.

DESCRIPTION

Wood diffuse-porous. Growth rings present, marked by marginal parenchyma bands ( Fig. 9A ). Vessels mostly solitary (70-90%) or grouped by 2-4 ( Fig. 9A ), round to oval, 1-7 per mm² (average 3); tangential diameter 100-300 µm (average 200 µm). Tyloses absent. Vessel elements 160- 570 µm (average 310 µm) long. Perforation plates simple ( Fig. 9E ). Intervessel pits alternate, 4-12 µm (average 8 µm) in diameter, apparently vestured ( Fig. 9G ). Axial parenchyma lozenge-aliform to weakly confluent when vessels are close to each-other, and in marginal bands 1-7 cells wide, sometimes merging with the aliform parenchyma of smaller vessels ( Fig. 9A ); diffuse sometimes present, larger than fibres cells, often in the vicinity of the rays but also scattered among fibres ( Fig. 9A, B ); parenchyma cells 40-145 µm (average 80 µm) long, 10-49 µm (average 25 µm) wide; 2-4 or more cells per parenchyma strands; crystals in chambered parenchyma cells ( Fig. 9E ) (up to 16 crystals per parenchyma strands), mostly in the margin of aliform parenchyma and diffuse parenchyma. Rays 1- to 3-seriate ( Fig. 9D ), storied in some places ( Fig. 9C ), sometimes not storied, varying within the same specimen and among individuals, ripple marks visible with the naked eye to a greater or lesser extent for all specimens, 5-12 rays per mm (average 8), 130-400 µm (average 240 µm) or 6-20 cells high, homocellular made of procumbent cells ( Fig. 9F ). Fibres thin to thick-walled (lumina 1.2 times the double wall thickness in average, for best preserved fibres), nonseptate, 8-26 µm (average 16 µm) wide, a storied tendency when it is the case for the rays.

DISCUSSION

Two out of three specimens (MNHN.F.50184 and MNHN.F.50185) are very similar in color and mineralization, and display the same compression, suggesting that they might represent different parts of the same broken piece. The third specimen (MNHN.F.50186) has a different preservation and deformation, bigger and less dense vessels, but shares all the key characters of the first two. They are characterized by: 1) diffuse-porous wood; 2) exclusively simple perforation plates; 3) lozengealiform parenchyma; 4) marginal bands of parenchyma; and 5) 1-3-seriate and storied rays. These specimens are very close to our Pahudioxylon bankurensis but display distinctive features that allow us to put them apart: the lozenge-aliform parenchyma is less extended, vessels (or vessel groups) are more separated from each other which leads to a lesser degree of confluence; clear diffuse parenchyma is present; the degree of storied structures is greater, as ripple marks are visible. No perfect match comes out on InsideWood (2004 -onward) with the storiation of rays taken into consideration as well as diffuse-parenchyma. These characters apart, our fossils share most features of Afzelia and Intsia species as well as of Pahudioxylon bankurensis . The two living genera are yet rarely described with diffuse parenchyma or storied rays. Soerianegara & Lemmens (1993) mention diffuse parenchyma in only a few Afzelia and Adenanthera L. species. The latter having no storied structures nor more than four cells per parenchyma strands ( InsideWood 2004 -onward). Diffuse parenchyma is mentioned in Afzelia africana Sm. ex Pers. and A. javanica (Miq.) J. Léonard ( Soerianegara & Lemmens 1993, InsideWood 2004 -onward, Feng et al. 2015), but they have no or faint storied rays (as seen in figures of Gérard & Louppe 2011). Storied tendency of the rays is mentioned for Intsia ( Ogata et al. 2008, Feng et al. 2015), A. rhomboideae (Blanco) Fern. -Vill. and can be seen in A. xylocarpa (Kurz) Craib. It is noteworthly that A. xylocarpa and A. martabanica (Prain) J.Léonard grow today in Myanmar ( Léonard 1950; POWO 2019; Haw 2019). The latter is restricted to this area, but no information on its wood anatomy or ecology is available. We consider that no single species can be assigned as NLR, but the genera Afzelia - Intsia as a whole regarding diffuse parenchyma.

Similarities are found between our specimens and Adenantheroxylon pavoninium Prakash & Tripathi (1968, 1969 ), but A. pavoninium has commonly 2-seriate rays, vasicentric parenchyma (rarely aliform) and no marginal parenchyma. Among species of Pahudioxylon , our specimens are very close to Pahudioxylon bankurensis as well as P. kiliani (Louvet) Prakash ( Prakash et al. 1967) . Storied rays (or a storied tendency) and diffuse parenchyma are only (and variably) found in P. bankurensis ( Feng et al. 2015) . The specimen no. 5790 of Vozenin-Serra & Privé-Gill (1989), attributed to the species P. sahnii (synonym of P. bankurensis ) displays the same diffuse parenchyma and portions of the wood with storied rays; in addition, Feng et al. (2015) also described some specimens of P. bankurensis for which the parenchyma is not in contact with vessels and could be interpreted as diffuse parenchyma ( Feng et al. 2015: 489, fig. 2K). These features seem to be variable among individuals of the same species and among the species of the same genus, and we do not consider them as diagnostic to establish a new species or to exclusively attribute the specimens to Pahudioxylon bankurensis . Consequently, we assign these specimens to Pahudioxylon cf. bankurensis .

Afzelia are tropical trees present in Africa and Asia at low elevation up to 400 m altitude ( Ali 1973; Hou et al. 1996; Orwa et al. 2009). Afzelia trees grow in mixed deciduous and dry evergreen forests, on well-drained soils and in periodically inundated lowlands ( Soerianegara & Lemmens 1993). The habitat of Intsia is given p. 868. Among the available species with sometimes diffuse parenchyma, Afzelia africana is tolerant to a wide range of climate from humid to dry forests, but is essentially found in the savanna woodland/dense dry forests borders and in semi-deciduous forests up to 1400 m altitude; it can also occur in lowland rainforests, dry forests, gallery forests, periodically inundated areas and savannas, but commonly requires annual rainfall above 900 mm ( Orwa et al. 2009; Gérard & Louppe 2011; Hills 2020); Afzelia javanica grows in primary and secondary forests, in dry places, mostly in lowlands up to 800 m altitude ( Hou et al. 1996). These two species, pending more comprehensive anatomical data on the genus, are considered as the most adequate NLR.

Figures

FIG. 9. — Pahudioxylon cf. bankurensis Chowdhury,Ghosh & Kazmi, MNHN.F.50184: A, Ts,mostly solitary vessels, aliform parenchyma with crystals in marginal cells (black arrow), marginal parenchyma (bottom) and diffuse parenchyma (white arrow); B, Ts, detail of diffuse parenchyma (white arrow), often in contact with rays; C, Tls, storied rays in some parts of the section;D, Tls,1-3-seriate homocellular rays in a non-storied part of the section; E, Rls, crystals in parenchyma strands, the strand on the left being diffuse parenchyma; F, Rls, homocellular ray; G, Tls, alternate intervessel pits, apparently vestured. Scale bars: A, 1 mm; C, 500 µm; B, D-E, 200 µm; F, 100 µm; G, 50 µm. Abbreviations: see Fig. 2.