Koompassioxylon elegans Kramer

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 : 864-865

Koompassioxylon elegans Kramer

( Fig. 6 )

Koompassioxylon elegans Kramer, 1974: 117 , pl. 27, figs 94, 95, 97- 101, 103, pl. 28, fig. 105, ill. 12a-c, 13.

ORIGINAL HOLOTYPE. — Senckenberg Museum, Frankfurt. no. SM.B 12 509/1-12 509/3

MATERIAL. — MNHN.F.50179 (field number: 17FN13) , MNHN.F.50180 (field number: 17FN14) , MNHN.F.50181 (field number: 19NAT03-2). Estimated minimal diameter:17-51(-81) cm ; 130-230 cm for specimen MNHN.50179

.

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.

AGE. — Upper lower to lowermost middle Miocene.

DESCRIPTION Wood diffuse-porous. Growth rings present, marked by marginal parenchyma bands ( Fig. 6A ). Vessels mostly solitary (70-90%) or grouped by 2 or 3 ( Fig. 6A ), oval, 0-6 per mm² (average: 3); tangential diameter 120-370 µm (average: 230). Tyloses absent. Vessel elements 160-570 µm long (average: 340). Perforation plates simple horizontal to slightly oblique. Vessel pits alternate, 6-11 µm (average: 8) in diameter, likely non-vestured (for specimen MNHN.F.50180, see Fig. 6C ). Vessel-ray pits not preserved. Parenchyma widely wingedaliform ( Fig. 6A, B ), also confluent laterally or in diagonal, forming anastomosed and/or band-like shapes, joining up to 10 vessels depending on the specimen and the position in the wood ( Fig. 6A ), also in 1-7 cells wide marginal bands enclosing some small vessels ( Fig. 5A ), maybe rare diffuse parenchyma; parenchyma cells 30-145 µm long (average: 85), 10-50 µm wide (average: 30); 4-8 or more cells per parenchyma strand; crystals in chambered parenchyma cells ( Fig. 6D, E ), especially in border ones. Rays 2- to 3-seriate (mainly 3, rarely 4) ( Fig. 6D, E ), tendency to storied arrangement resulting in discreet ripple marks visible in some parts with the naked eye ( Fig. 6F ), 3-10 rays per mm (average: 7), 160-490 µm (average: 340 µm) or up to 18 cells high, heterocellular with 1-2 rows of upright or square cells at both ends ( Fig. 6G ); 1-2 crystals in upright ray cells, sometimes subdivided ( Fig. 6G ). Fibres thin-to-thick walled (lumina about 0.84 times the double wall thickness), non-septate, 8-22 µm (average: 14 µm) wide. DISCUSSION

These specimens are characterized by: 1) diffuse-porous wood; 2) large vessels (> 200 µm); 3) exclusively simple perforation plates; 4) crystalliferous winged-aliform and confluent parenchyma; 5) marginal parenchyma bands; 6) 2- to 3-seriate rays with a storied tendency; 7) low vessel density; 8) heterocellular rays; and 9) crystalliferous rays. Aliform parenchyma, marginal parenchyma and 2-3 seriate rays are common features in Fabaceae . Modern analogs with all characteristics cited above have not been found on InsideWood (2004 -onward), but a less restrictive code (5p 13p 22p 40a 48a 49a 50a 65a 80p 82p 83p 89p 96a 97p 99a 105a 108a 109a 116a 136p 137p 142p with 0 mismatches) shows similarities with: Dalbergia assamica Benth. ; Distemonanthus benthamianus Baill. ; Angylocalyx Taub. ; Desmodium oojeinense (Roxb.) Ohashi ; and several species of Ormosia Jacks. which either lack storied features, crystals, have all elements storied or diffuse parenchyma ( InsideWood 2004 -onward, Ogata et al. 2008). When considering the possible non-vestured pits of one of our specimens, Kalappia celebica Kosterm. and Koompassia Maingay ex Benth. are the closest genera, but the former has well-marked storied rays with no crystals in marginal cells ( Ogata et al. 2008). Koompassia is thus the best living relative as it has irregularly storied rays, non-vestured pits, crystals in rays and parenchyma, aliformconfluent, sometimes winged-aliform parenchyma and marginal parenchyma bands.The preservation state of our specimens is yet not good enough to determine whether the pits are vestured or not for all the specimens. In this genus, K. excelsa (Becc.) Taub. has more often banded parenchyma, often crystals in upright ray cells; K. malaccensis Benth. bears the closest resemblance with our specimens, and has aliform-confluent parenchyma, sometimes pointed at the extremities, but less often crystals in upright ray cells than K. excelsa ( Soerianegara & Lemmens 1993; InsideWood 2004 -onward; Ogata et al. 2008).

Kramer (1974) defined the fossil genus Koompassioxylon for fossils resembling Koompassia ( K. malaccensis more specifically). The genus Koompassioxylon is thus described with marginal parenchyma, vessel-ray pits similar to intervessel pits, crystalliferous aliform-confluent to winged aliform parenchyma, 2-4 seriate rays with irregularly storied pattern, heterocellular rays with at least one row of upright marginal cells, sometimes subdivided with crystal included. In opposition to the modern relative Koompassia , which has non-vestured intervessel pits, Koompassioxylon has vestured intervessel pits.The genus Ormosioxylon Bande & Prakash was described by Bande & Prakash (1980) for wood specimens resembling Ormosia . Although the two diagnoses significantly overlap, Ormosioxylon is described without any mineral inclusion, which is not compatible with our specimens.

Vestured/non-vestured intervessel pits are very delicate to observe in fossils and should be considered whith great caution according toWheeler et al. (2020).With this limitation in mind, our fossils share most of the features of Koompassioxylon . Among the two species of Koompassioxylon , K. keralaensis Srivastava & Awasthi (1996) has less frequent confluent parenchyma, mostly homocellular rays, irregularly storied parenchyma and rays, and no crystals; by contrast, K. elegans is more similar to our fossil specimens as it has marginal parenchyma, as well as pointed aliform-confluent with crystals, weakly heterocellular rays with crystalliferous upright marginal cells, a storied ray tendency, but it has mainly 2-seriate rays (compared to mainly 3-seriate in our specimens). This minor difference aside, and with the exception of possibly non-vestured pits, our specimens are compatible with the diagnosis of K. elegans .

Koompassia is a genus of Southeast Asian tropical trees growing in primary rainforests, coastal plain, foothills, ridge slopes and river valleys, and occasionally in peat and freshwater swamps, below 650 m altitude ( Soerianegara & Lemmens 1993; Lewis et al. 2005). Koompassia are large trees, often dominating the canopy; the large estimated diameter of our specimens is in adequacy with this genus of ‘giant’ trees. Indeed, they can grow up to 85 m tall, with a diameter up to 290 cm ( Soerianegara & Lemmens 1993). Koompassia malaccensis lives in lowland forests and in freshwater peat and swamp forests, as well as in dry lands up to 150 m altitude (rarely up to 800 m; Soerianegara & Lemmens 1993; Hou et al. 1996).

Figures

FIG. 6. — Koompassioxylon elegans Kramer, MNHN.F.50180 (A-E, G), MNHN.F.50181 (F): A, Ts, vessel size and groups, aliform parenchyma with pointed wings and marginal parenchyma sometimes merged with small vessels (arrow); B, Ts,detail of winged-aliform parenchyma;C, Tls,non-vestured,alternate and polygonal intervessel pits; D, Tls, 2-3-seriate rays with crystalliferous parenchyma (arrow); E, Tls, detail of the chambered crystalliferous parenchyma (arrow); F: storied ray tendency, mostly 2-3-seriate rays; G, Rls, heterocellular rays with crystals in upright (sometimes subdivided) marginal cells (arrow). Scale bars: A, 1 mm; F, 500 µm; B, D-E, G, 200 µm; C, 20 µm. Abbreviations: see Fig. 2.

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.