Cynometroxylon parainaequifolium Prakash

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 : 862-864

Cynometroxylon parainaequifolium Prakash ( Fig. 5 A-G)

Cynometroxylon parainaequifolium Prakash, 1979: 51 , pl. 2, figs 5, 7.

ORIGINAL HOLOTYPE. — Birbal Sahni Institute of Palaeosciences Museum no. 35263

MATERIAL. — MNHN.F.50176 (field number: 17FN10) , MNHN.F.50177 (field number: 19NAT07-1) , MNHN.F.50178 (fieldnumber: NAT17-7). Estimated minimal diameter: 9-20 cm (> 50 cm for specimen MNHN.F.50178, which has almost parallel rays).

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.

AGE. — Upper lower to lowermost middle Miocene.

DESCRIPTION

Wood diffuse-porous. Growth rings hardly distinguishable marked by small marginal parenchyma bands, a change in vessel or fibres band size or growth line ( Fig. 5A ). Vessels solitary (40-75%) or in radial groups of 2-5, round to oval, 3-16 per mm² (average 8 per mm²); tangential diameter 50-170 µm (average: 120 µm) ( Fig. 5A, F, G ). Tyloses absent. Vessel elements 150-600 µm (average: 330 µm) long. Perforation plates simple, sometime slightly oblique. Intervessel pits alternate, 2-4 µm wide (average: 3 µm) ( Fig. 5E ). Parenchyma mostly banded but also aliform or vasicentric close to growth rings, bands wavy and sometimes anastomosed, enclosing most of vessels ( Fig. 5A, F, G ), 3-8 cells wide (average: 5 cells), as large as fibres bands or thinner, 3-5 bands per mm; parenchyma cells 35-160 µm (average: 100 µm) long, 10-36 µm (average: 22 µm) wide in tangential section; 5 to 8 cells per parenchyma strands, crystals sometimes present in chambered parenchyma cells ( Fig. 5D ). Rays 1- to 3-seriate (mostly 2-seriate) ( Fig. 5B, C ), 6-13 rays per mm (average: 9 per mm), 140-1080 µm (average: 470 µm) or up to 35 (sometimes 55) cells long, heterocellular made of procumbent cells with 1-3 square or upright marginal cells ( Fig. 5C ), sometimes end-to-end fusions resulting in very high rays. Fibres non-septate, 5-20 µm in tangential diameter (average 13 µm), thin- to thick-walled (lumina about 0.42 times the double wall thickness).

DISCUSSION

This specimen has: 1) diffuse-porous wood; 2) banded parenchyma about as thick as fibres bands; 3) 1-3 seriate heterocellular rays; 4) non-septate fibres; and 5) non-storied elements. Similar to our previous Cynometroxylon specimens, these three specimens are comparable to extant Cynometra . They also are remarkable in having thinner parenchyma bands (around 5 cells high), higher rays and frequent ray fusions.

They display a close resemblance to Cynometra polyandra because of its variability of parenchyma pattern and ray width, and to Cynometra inaequifolia A. Gray because of its ray width and the occasional presence of long rays (up to 1 mm long) ( InsideWood 2004 -onward).

These specimens also share all the diagnostic features of the genus Cynometroxylon . Rays are rarely uniseriate and always heterocellular, parenchyma bands are mostly wavy, which make them somehow compatible with the diagnosis of Crudioxylon Pons (1980) as well. When compared with other Cynometroxylon , our specimens resemble closely to C. parainaequifolium , which also has small vessels (<200 µm of diameter),parenchyma bands 2-7 cells wide, and sometimes long rays (up to 60 cells high) with frequent fusions. Our specimens have a slightly higher density of vessels and display sometimes 3-seriate rays (only 1-2-seriate reported in C. parainaequifolium ). Two out of three of our fossil specimens display parenchyma bands that are sometimes discontinuous ( Fig. 4A, D ) which is not in the diagnosis of C.parainaequifolium . MNHN.F.50176 is the specimen where this morphology is the most visible ( Fig. 4 A-C). These differences could yet be explained by intra-individual variations, as proposed by Pons (1980) for Crudioxylon. Discontinuous bands and aliform parenchyma are also observed in the Cynometroxylon holdeniae specimen of Boonchai (2008) and the fossil Cynometra grandis Woodcock, Meyer & Prado specimen ofWoodcock et al. (2017). It is also visible in extant Cynometra ananta and Cynometra polyandra of InsideWood (2004 -onward) and Boonchai (2008: 111-112, fig. 4.41, fig. 4.42). An examination of the specimen MNHN-P-P00395888 of C. polyandra reveals that parenchyma arrangement and band width can change throughout the life of the tree.We thus consider that discontinuous bands in Cynometra and Cynometroxylon are a variable character and not a diagnostic feature of our fossils. All these observations lead us to attribute these three specimens to Cynometroxylon parainaequifolium .

Cynometra inaequifolia is a small lowland tree (up to 20m tall) of Malaysia, Philippines, and Thailand resembling C. ramiflora (Knaap-van Meeuwen 1970; Soerianegara & Lemmens 1993; Hou et al. 1996; World Conservation Monitoring Centre 1998). Cynometra polyandra is a wet evergreen or semi-evergreen forest tree species (Knaap-van Meeuwen 1970; Soerianegara & Lemmens 1993), found up to at 1300 m altitude (Knaap-van Meeuwen 1970; Hou et al. 1996; World Conservation Monitoring Centre 1998).

Figures

FIG. 5. — Cynometroxylon parainaequifolium Prakash,MNHN.F.50176 (A-C, E), MNHN.F.50177 (D, F), MNHN.F.50178 (G): A, Ts, vessels, parenchyma alternately banded, aliform and vasicentric, growth limits between arrows; B, Tls, 1-3 seriate rays, non-septate fibres; C, Rls, heterocellular rays with 1-2 rows of marginal cells (arrows); D, Tls, mostly 2-seriate rays with parenchyma sometimes crystalliferous (arrow); E, Tls, alternate intervessel pits; F, Ts, banded and aliform parenchyma; G: Ts, banded and aliform parenchyma. Scale bars: A, 1 mm; F-G, 500 µm; B, D, 200 µm; C, 100 µm; E, 50 µm. Abbreviations: see Fig. 2.

FIG. 4. — Cynometroxylon holdeniae (Gupta) Prakash & Bande, MNHN.F.50174 (A, D-G), MNHN.F.50173 (B, C): A, Ts, banded parenchyma and vessel arrangement; B, Ts, detail of the wounded part of the wood with irregular pattern of parenchyma, vessels are absent; C, Ts, wounded part (white segment) in between the normal wood; D, Ts, detail of banded parenchyma 2-11 cells wide bands; E, Tls, heterocellular and mostly 2-seriate rays; F, Tls, minute alternate intervessel pits; G, Rls, heterocellular rays with 1-2 rows of marginal ray cells. Scale bars: A, C, 1 mm; B, D, E, G 200 µm, F, 50 µm. Abbreviations: see Fig. 2.