Dryobalanoxylon cf. javanense (Kräusel)

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 : 878-879

Dryobalanoxylon cf. javanense (Kräusel) Den Berger ( Fig. 13 )

Dipterocarpoxylon javanense Kräusel, 1922: 9-15 , figs 1-5, ill. 1-2.

Dryobalanoxylon javanense – Den Berger 1927: 497, 498.

ORIGINAL HOLOTYPE. — Mineralogical-Geological Institute of the University of Groningen, no. unknown.

MATERIAL. — MNHN.F.50190 (field number: 17FN20). Estimated minimal diameter: 30 cm.

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.

AGE. — Upper lower to lowermost middle Miocene.

DESCRIPTION

Wood diffuse-porous.Growth rings indistinct or absent.Vessels almost exclusively solitary (90-95%), oval due to compression ( Fig.13A ), 3-8 per mm² (average: 5); tangential diameter 130- 260 µm (average: 180 µm). Tyloses present ( Fig. 13C ). Vessel elements 230-610 µm long (average: 450 µm). Perforation plates simple.Intervessel pits alternate.Vessel-ray pits apparently simple, up to 5 per cell; 8-20 µm long, 3-9 µm large ( Fig. 13F ). Fibre-tracheids and vasicentric tracheids present ( Fig. 13D ). Axial parenchyma scanty paratracheal to mostly vasicentric and diffuse, occasionally slightly aliform, also forming more or less continuous bands of 3-10 cells thick that may contain secretory canals ( Fig. 13B ). Bands of parenchyma are closely spaced but their relative arrangement is difficult to determine due to compression and bad preservation. Parenchyma cells 80-100 µm long (average: 90), 15-30 µm wide (average: 20) wide, more than 8 cells per parenchyma strand; crystals absent. Parenchyma abundant visible in tangential section. Rays with a two-size tendency; 1- to 6-(7-)seriate, mainly 4- to 6-seriate with 5-seriate being the most frequent, uniseriate regularly present made of (up to 15) procumbent and square or upright cells ( Fig. 13D ), 3-7 rays per mm (average: 5), 330-1530 µm (average:830 µm) or up to 50 cells high or more, heterocellular made of procumbent cells with 1-4 square or upright cells at one or both ends (once seen with 9 cells) ( Fig. 13H ), sheath cells present and easily distinguishable ( Fig. 13D ). Fibres thinto-thick walled (lumina 0.7 times the double wall thickness in average) to very-thick walled, non-septate, 10-22 µm wide (average: 16 µm). Numerous canal lines, embedded in parenchyma bands ( Fig. 13B ). They can be from 1 to 5 canals long ( Fig.13E ), possibly longer as vessel walls are not always preserved and can be confused with canals. At least one long tangential line of canals crossing the section from edge to edge ( Fig. 13A, B ); vessels often interrupting the line. We thus considered only unmistakable canals.Tangential diameter 40-120 µm (average: 80). Silica bodies (?) present in ray cells ( Fig. 13G ).

DISCUSSION

This specimen is characterized by: 1) diffuse-porous wood; 2) exclusively simple perforation plates; 3) large and mostly solitary vessels; 4) axial canals in long and short lines; 5) vasicentric tracheids and fibre-tracheids; 6) heterocellular rays, often higher than 1 mm; and 7) vasicentric and diffuse parenchyma. These combined features indicate an affinity with extant Dipterocarpaceae , which are often characterized by secretory canals and vasicentric tracheids. Mostly solitary vessels, fibre-tracheids and long tangential lines of secretory canals are diagnostic of the genus Dryobalanops ( Schweitzer 1958) . However, due to the poor preservation of this fossil, many cell walls (especially for vessels) are not preserved; it is thus difficult to distinguish small vessels from canals and precisely assess vessel and canal diameter. Parenchyma is also not always identifiable everywhere. Although we identified a clear long line of canals, apparently embedded in a tangential band of parenchyma, many other short lines of canals are found throughout the section ( Fig. 13B ). Because of the compression, we cannot always determine if a band of parenchyma is tangentially connecting these canals. Some species of Dipterocarpus have canals grouped in long lines (as mentioned in InsideWood 2004 -onward for D. indicus Bedd. , D. baudii Korth. and D. turbinatus C.F.Gaertn. ; also seen in the specimen MNHN-P-P00402617 of D. turbinatus ). A compressed and decayed fossil wood could easily display closely spaced short tangential lines that appear as a single long line. But the presence of fibre-tracheids, tyloses and silica bodies (?) in ray cells suggest a closer affinity with Dryobalanops ( Metcalfe & Chalk 1950; Schweitzer 1958; Gottwald & Parameswaran 1966; Soerianegara & Lemmens 1993; Ogata et al. 2008). Our specimen resembles closely to Dryobalanops keithii Sym. and D. lanceolata Burck for ray width mostly 4-5 seriate, parenchyma vasicentric to aliform, few diffuse and interruption of long tangential lines of canals; and to D. oblongifolia Dyer for its ray width (up to 6- or 7-seriate), shape of rays, quite abundant diffuse parenchyma, and canal distribution (also interrupted by vessels). The latter being the most resembling all things considered.

This fossil is attributed to the genus Dryobalanoxylon because of the presence of a long tangential line of canals, solitary vessels and visible fibre-tracheids. A comparison with the most resembling Dryobalanoxylon species shows that most of them have rays up to 4-5-seriate. Among species with wider rays ( Appendix 1; Den Berger 1923; Boureau 1952; Schweitzer 1958; Awasthi 1971; Srivastava & Kagemori 2001; Mandang & Kagemori 2004), D. bogorense Srivastava & Kagemori has rays up to 6-seriate, but more abundant parenchyma with aliform being present, as well as no sheath cells; D. khmerinum Boureau has up to 7-seriate rays but shorter rays, bigger canals and smaller vessels; D. javanense of Schweitzer (1958) has rays up to 6-seriate rays, as well as long lines and few short lines of 2-4 canals; D. cf. bangkoense of Schweitzer (1958) has rays up to 7-seriate. The last two are very similar to each other and share most features of our fossil, with some minor differences: D. javanense has slightly thinner and shorter rays, mostly scanty paratracheal parenchyma (compared to mostly vasicentric) and very pronounced sheath cells. Dryobalanoxylon cf. bankgoense has a lesser proportion of solitary vessels, a greater amount of apotracheal parenchyma (diffuse-in-aggregate is mentioned) and has no sheath cells described. We do not consider that these differences are enough to describe a new species; neither too few to attribute this fossil to any species. We thus attribute this fossil to Dryobalanoxylon cf. javanense as it is the only specimen described with both long and short lines of secretory canals.

Most Dryobalanoxylon specimens are recorded in Indonesia ( Appendix 1; Schweitzer 1958; Srivastava & Kagemori 2001) but they are also found in Vietnam, Cambodia, India ( Appendix 1; Srivastava & Kagemori 2001) and Myanmar ( Gottwald 1994). Our fossil is the second record of Dryobalanoxylon in Myanmar.

Dryobalanops is today exclusively present in southeast Asia and absent in India and Myanmar (Maury-Lechon & Curtet 1998; Ghazoul 2016). It is a genus of tropical canopy trees growing on hillsides or along streams, at up to 800 m altitude; they are also present in lowland dipterocarp forests, mixed peat-swamp forests, sometimes also in heath forests ( Ashton 1982; Soerianegara & Lemmens 1993). Dryobalanops oblongifolia lives in lowland mixed dipterocarp forests, also in periodically inundated, freshwater swamps, near streams, in poorly drained forests or on hillsides below 600 m ( Ashton 1982; Soerianegara & Lemmens 1993; Barstow 2018a). Dryobalanops keithii always occurs near water on lowlands and foothills up to 250 m altitude ( Ashton 1982; Soerianegara & Lemmens 1993; Randi et al. 2019). Dryobalanops lanceolata lives in mixed dipterocarp forests and can occur in logged (open) forests, on clay soils and rolling hills up to 700 m altitude ( Ashton 1982; Bodos et al. 2019).

Figures

FIG. 13. — Dryobalanoxylon cf. javanense (Kräusel) Den Berger, MNHN.F.50190:A, Ts,Vessels seemingly exclusively solitary and long tangential line of secretory canals embedded in parenchyma bands (between arrows); B, Ts,synthetic drawing of the transversal section (with only some vessels and rays displayed); visible bands of parenchyma as grey lines and secretory canals as red dots, arranged mostly in long tangential lines; C, Ts, tyloses in vessels (arrow); D, Tls 1-6 seriate rays with some sheath cells (white arrows), vasicentric tracheids (black arrows) and fibre-tracheids (grey arrow); E, Ts, detail of secretory canals embedded in tangential bands of parenchyma; F, Rls, simple vessel-ray pits with reduced borders in irregular shapes; G, Rls, silica bodies (?) in ray cells; H, Rls, heterocellular ray with mostly 1-4 rows of square or upright marginal cells. Scale bars: B, 1 cm; A, 1 mm; C-E, H, 200 µm; F-G, 50 µm.