Albizinium eolebbekianum 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 : 858-860

Albizinium eolebbekianum Prakash

( Fig. 3 )

Albizinium eolebbekianum Prakash, 1975: 197 , pl. 3, figs 9, 11, 12.

ORIGINAL HOLOTYPE. — Birbal Sahni Institute of Palaeosciences Museum no. 150/1014.

MATERIAL. — MNHN.F.50172 (field number: 17FN04). Estimated minimal diameter: 30 cm.

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar

AGE. — Upper lower to lowermost middle Miocene

DESCRIPTION

Wood diffuse-porous. Growth ring boundaries indistinct. Vessels mostly solitary (80%) or grouped by 2, rarely 3, oval, 0-5 per mm² (average: 2) ( Fig. 2A, B ); tangential diameter 140-260 µm (average: 210 µm). Tyloses absent. Vessel elements 180-460 µm long (average: 290 µm). Perforation plates simple, mostly horizontal to slightly oblique ( Fig. 3C ). Intervessel pits alternate, polygonal in shape and crowded, 6-10 µm in size ( Fig. 3C ). Vessel-ray pits not preserved. Axial parenchyma lozenge-aliform, sometimes confluent, and seemingly marginal bands ( Fig. 3A, B ); also, maybe some diffuse parenchyma; parenchyma cells 100-150 µm (average: 120 µm) long in tangential plan, 20-50 µm (average: 30 µm) wide; crystals present in chambered cells ( Fig. 3D ). Rays 1- to 3-seriate (mainly 2), non-storied, 5-8 rays per tangential mm (average: 6), 150-340 µm (average: 220 µm) or 5-20 cells high ( Fig. 3D ), homocellular made of procumbent cells ( Fig. 3F ). Fibres with poorly preserved walls, septa present in some fibres ( Fig. 3D, E ), 15-22 µm wide (average: 18 µm).

DISCUSSION

This specimen is characterized by: 1) diffuse-porous wood; 2) exclusively simple perforation plates; 3) aliform parenchyma; 4) the presence of septate fibres; and 5) homocellular and mostly 2- to 3-seriate rays.

These characters suggest affinities with modern Fabaceae and particularly with the traditional Mimosoideae subfamily (now in the recircumscribed Caesalpinioideae subfamily) (LPWG 2017). In InsideWood (2004 -onward), 35% of described specimens of the traditional Mimosoideae have septate fibres. Ogata et al. (2008) also indicate that homocellular rays are mostly found in Mimosoideae. In modern wood of Mimosoideae, the lozengealiform parenchyma combined with the presence of septate fibres and homocellular rays is mainly found in genera Albizia , Inga Mill. and Pithecellobium Mart. ( InsideWood 2004 -onward). Pithecellobium , however, has higher and wider rays ( Awasthi 1979). Albizia and Inga share a close anatomy.According toEvans et al. (2006), Inga has slightly more frequent radial multiples of vessels, as well as confluent parenchyma. A comparison with specimens and plates available onInsideWood (2004-onward) also reveal higher and thinner rays for Inga (frequently with uniseriate portion, and 2-seriate), with more often uniseriate rays, wheareas most of Albizia species have fusiform and shorter rays. Thus, our specimen shows closer similarities to the genus Albizia , including three specific species: Albizia lebbeck (L.) Benth., regarding its parenchyma arrangement, the presence of septate fibres and non-septate fibres. However, it often has wider rays (up to 5-seriate); A. ferruginea (Guill. & Perr.) Benth. for its lozenge-aliform parenchyma and vessel density, resulting in a few confluences, similar ray size; and A. procera (Roxb.) Benth. for its aliform parenchyma rarely confluent and similar ray size (1-3 seriate, fusiform).

Fossil wood specimens resembling Albizia species are designated under the genus Albizinium (Prakash 1975) or described as Albizia ( Gregory et al. 2009) . The features of the present specimen are compatible with the diagnosis of Albizinium. Although the anatomically close genus Acrocarpoxylon Gottwald has aliform parenchyma and septate fibres, it has more often heterocellular rays ( Gottwald 1994). Among Albizinium fossil species close to our fossil ( Awasthi 1979; Prakash et al. 1994; Mehrotra et al. 1999), A. eolebbekianum has shorter rays (up to 280 µm compared to 340 µm in our fossil) and A. pondicherriensis Awasthi has a higher ray density (10-15 / mm as opposed to 5-8 / mm) and more frequent vessels in groups than our fossil. The diagnoses of A. eolebbekianum and A. pondicherriensis are remarkably similar. Our fossil resembles A. eolebbekianum from the Miocene of India for the proportion of solitary vessels and the parenchyma arrangement, whereas it resembles more A. pondicherriensis for ray and vessel size. Our specimen is in fine attributed to A. eolebbekianum given the propensity of A. pondicherrienses to form vessel groups.

Albizia species are tropical or subtropical trees occurring in open secondary vegetation, in primary deciduous to monsoonal forests, and in savannas and shrublands of Asia, Africa, and America, up to 1700 m altitude ( Nielsen 1992; Sosef et al. 1998). Albizia lebbeck is a deciduous tree, probably native to tropical mainland Asia or East-Africa, mostly cultivated or naturalized. It grows in monsoonal semi-evergreen forests and monsoonal dry-deciduous forests with mean annual rainfall of 1300-1500 mm and very dry winter, at low elevation (0-750 m, sometimes up to 1700 m). It is also found along rivers and sand beaches. It is resistant to long hot and dry periods as well as cold winters and tolerates a wide range of soils including sandy river beds, coral loam or limestone (Prakash 1975; Nielsen 1992; Jensen 1999; Orwa et al. 2009; Wu et al. 2010); A. ferruginea is only found in Africa, mainly in lowlands, semi-deciduous forests, but also in evergreen forests, rainforests, and savannas ( Sosef et al. 1998; Orwa et al. 2009). Albizia procera is found across all Southeast Asia and is tolerant to a wide range of climates; it is mostly found in open secondary forests and in areas with a pronounced dry season, as well as in grasslands, savannas, monsoon forests or swamp forests and rainforests up to 1500 m altitude ( Nielsen 1981, 1992) in areas with more than 2500 mm of annual rainfall and mean annual temperature of 21-32°C ( Orwa et al. 2009).

Figures

FIG. 3. — Albizinium eolebbekianum Prakash, MNHN.F.50172: A, Ts,vessels and parenchyma arrangement,marginal parenchyma band (arrow); B, Ts, lozengealiform parenchyma, sometimes confluent, fibres radialy aligned; C, Tls, alternate intervessel pits, simple perforation plates; D, Tls, 1-3-seriate rays, septa (black arrows) and crystalliferous parenchyma (white arrow); E, Tls, detail of a septate fibre; F, Rls, homocellular ray. Scale bars: A, 1 mm; B, 500 µm; D, 200 µm; C, F, 100 µm; E, 25 µm. Abbreviations: see Fig. 2.

FIG. 2. — Cupressinoxylon sp. MNHN.F.50171: A, transverse section (Ts), growth limits (white arrows), diffuse parenchyma (grey arrows) and zonate parenchyma (black arrows), large black areas are cells filled with deposit material; B, Ts, growth limit with gradual transition from earlywood to latewood; C, tangential longitudinal section (Tls), 1- sometimes 2-seriate rays and parenchyma lines (arrow); D, Tls, detail of 1- sometimes 2-seriate rays; E, Tls, smooth longitudinal parenchyma walls (arrows); F, Tls, 1-2-seriate rays and tangential pits (arrows); G, radial longitudinal section (Rls), possibly cupressoid and/or podocarpoid crossfield pits (arrow); H, Rls, uniseriate radial pits; I, Rls, smooth parenchyma cell walls.Scale bars: A, C, 1 mm; B, 200 µm; E-F, H, 100 µm; G, 50 µm; I, 20 µm.