Cynometroxylon holdeniae (Gupta)

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 : 860-862

Cynometroxylon holdeniae (Gupta) Prakash & Bande ( Fig. 4 )

Dipterocarpoxylon holdenii [sic] Gupta, 1935: 633, pl. 64.

Cynometroxylon indicum Chowdhury & Ghosh, 1946: 435 , pl. 10- 11, text-fig. 5-9

Cynometroxylon schlagintweitii Müller-Stoll & Mädel, 1967: 130 , pl. 33, fig. 57, pl. 34. figs 59-62, ill. 8

Cynometroxylon cf. indicum – Prakash 1967: 93.

Cynometroxylon sp. cf. indicum – Prakash 1978: 383, pl. 3, figs 12-14.

Cynometroxylon holdeniae Prakash & Bande, 1980: 266 , pl. 3, figs 11-14 (‘ holdenii ’).

Cynometroxylon siwalicus Trivedi & Ahuja, 1978: 638 , figs 1-3.

NOTE ON NOMENCLATURE. — According to the article no. 60.8 of the International Code of Nomenclature for algae, fungi, and plants ( Turland et al. 2018), the specific epithet “ holdenii ” (or “ holdeni ”), derived from the personal name of Miss Ruth Holden, has to be treated as an error and corrected to “ holdeniae ”, a feminine name.

ORIGINAL HOLOTYPE. — Birbal Sahni Institute of Palaeosciences Museum no. 29785.

MATERIAL. — MNHN.F.50173 (field number: 17FN17) , MNHN.F.50174 (field number: 17FN19) , MNHN.F.50175 (field number: NAT17-3). Estimated minimal diameter: 8-38 cm. The specimen MNHN.F.50175 shows a differential growth as seen in modern Cynometra polyandra Robx. (MNHN-P-P00395888)

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LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.

AGE. — Upper lower to lowermost middle Miocene.

DESCRIPTION

Wood diffuse-porous. Growth rings indistinct or weakly distinguishable by a change of parenchyma and fibres band thickness and the presence of narrow marginal parenchyma bands. Vessels mostly solitary (60-80%) or in radial groups of 2-4, round to oval, 3-24 per mm² (average: 10 per mm²) ( Fig. 4A ); tangential diameter 50-200 µm (average: 115 µm). Tyloses absent. Vessel elements 130-510 µm (average: 300 µm) long. Perforation plates simple, oblique to horizontal. Intervessel pits alternate, seemingly polygonal, 2-5 µm wide (average: 3 µm) ( Fig. 4F ). Parenchyma paratracheal, vasicentric with 1-3 cells thick sheath around vessel and in continuous, wavy and sometimes anastomosed tangential bands, 2-11 cells wide (average: 7 cells), as large as fibres bands or thinner, including most of the vessels, 2-6 bands per tangential mm ( Fig. 4A, D ); parenchyma cells 40-100 µm (average: 72 µm) long, 9-40 µm (average: 19 µm) wide in tangential section; 4-6 (average: 5) cells per parenchyma strand, sometimes crystals in chambered parenchyma cells. Rays 2- to 3-seriate (mostly 2) ( Fig. 4E ), 8-13 rays per tangential mm (average: 10 per mm), 150-740 µm (average: 310 µm) or 7-35 cells long, heterocellular made of procumbent cells with 1 (or 2) square or upright cells at both ends ( Fig. 4G ), occasionally with a faint storied tendency. Fibres libriform, non-septate, 8-22 µm in tangential diameter (average 14 µm), thin- to thick-walled (lumina about 0.42 times the double wall thickness), without any particular arrangement ( Fig. 4D ). Wound healing zone marked by alternating bands of fibres and parenchyma but less continuous and regular than in the normal wood ( Fig. 4C ), parenchyma bands 1-5 cells wide; no vessel present; rays are mostly continuous throughout the wounded area. This pattern recalls debarking events ( Fig. 4C ).

DISCUSSION

These fossils are characterized by: 1) diffuse-porous wood; 2) exclusively simple perforation plates; 3) banded parenchyma as thick as fibres bands; 4) heterocellular and mainly 2-seriate rays; 5) a slight tendency to storied rays; and 6) non-septate fibres. The presence of a debarking healing zone is not considered for wood identification because it is a life event, independent of the wood traits. Thus, the most discriminant feature is the presence of banded parenchyma. According to the classification of Chowdhury & Ghosh (1946), our specimens belong to the group of angiosperms with parenchyma bands of the same (or almost) size as fibres bands (less than 30 cells wide). Following the identification of these authors leads to the Fabaceae .

Within extant Fabaceae , the present fossil specimens display similar features to the ones of genera Cynometra, Crudia Schreb. and Maniltoa Scheff. (synonym of Cynometra ) inlcuding heterocellular rays, only one size of vessels, and vessels included in parenchyma bands ( Chowdhury & Ghosh 1946; Carlquist 2001). Even though these species are hardly distinguishable from each other based on wood anatomy (Vozenin-Serra & Privé- Gill 1989; Soerianegara & Lemmens 1993; Ogata et al. 2008), Crudia is presumed to have larger and thicker parenchyma bands than Cynometra (Vozenin-Serra & Privé-Gill 1989) .

Cynometra and Maniltoa are extremely close genera, and Radosavljevic (2019) recently put the genus Maniltoa as a synonym of Cynometra . Cynometra ramiflora L. and Cynometra polyandra (synonym: Maniltoa polyandra (Roxb.) Harms ) are the most anatomically similar species to our fossils, especially concerning ray arrangement and composition, vessel size, and parenchyma band arrangement.

Fossil wood specimens resembling Cynometra are described under the fossil genus Cynometroxylon ( Chowdhury & Ghosh 1946) . All characters cited above fit with its diagnosis. Superficial resemblance with the genus Millettioxylon Awasthi can be pointed out, but the obvious storied character of rays, parenchyma and vessel elements, in addition to frequently homocellular rays dismiss this analogy ( Awasthi 1967). We compare our fossils to some Cynometroxylon already described in the literature. The specimens MNHN.F.50173 and MNHN.F.50174 display a closer resemblance with C. holdeniae , especially with the Burmese specimens described by Prakash & Bande (1980) from the Mio-Pliocene and by Licht et al. (2014) from the middle Eocene. They show a slightly higher density of vessels (7-24 per mm² for our fossils as opposed to 3-4 per mm² for C. holdeniae ), which might be related to environmental factors and is not enough to exclude their attribution to this species. The specimen MNHN.F.50175 shows some variations of character such as irregular size of bands, both for parenchyma and fibres, which could be interpreted as growth zones. These irregular bands are seen in extant Cynometra (e.g. Cynometra ananta Hutch. & Dalziel , Cynometra polyandra: InsideWood 2004 -onward). In some places, a storied tendency is observed.

Among Cynometroxylon specimens, only C. schlangintweitti and C. tunesense Delteil-Desneux are described with a storied ray tendency, but both have homocellular rays (Müller-Stoll & Mädel 1967; Delteil-Desneux 1980). Only some specimens of C. holdeniae have crystalliferous parenchyma ( Chowdhury & Ghosh 1946; Müller-Stoll & Mädel 1967; Awasthi 1992; Boonchai 2008). Thus, except for the irregular bands, all these features have been described in Cynometroxylon , but not all in the same specimen. Considering the variability seen among Cynometroxylon , all our specimens are attributed to Cynometroxylon holdeniae .

Cynometra species are pantropical shrubs or trees ( Lewis et al. 2005), though Radosavljevic (2019) recently excluded African species from the genus (except species from Madagascar). They are found in forests up to 1300 m altitude, often along rivers, on swampy soils, in dense wet lowland forests, or mixed with mangrove species ( Soerianegara & Lemmens 1993; Hou et al. 1996), and also in seasonally dry forests ( Lewis et al. 2005). Cynometra ramiflora is present in tidal forests of Myanmar, South India, Sri-Lanka, Andaman Islands and Malay Peninsula (Privé-Gill et al. 2004), in the back-mangrove forests and inland up to 400 m altitude ( Soerianegara & Lemmens 1993; Hou et al. 1996). Cynometra polyandra is a wet evergreen or semi-evergreen forest tree (Knaap-van Meeuwen 1970; Soerianegara & Lemmens 1993), found up to 1300 m altitude ( Soerianegara & Lemmens 1993; Hou et al. 1996).

Figures

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.