Artocarpoxylon kartikcherraensis Prakash & Lalitha

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 : 871-872

Artocarpoxylon kartikcherraensis Prakash & Lalitha ( Fig. 10 )

Artocarpoxylon kartikcherraensis Prakash & Lalitha, 1978: 132 , fig. 1.

ORIGINAL HOLOTYPE. — Birbal Sahni Institute of Palaeosciences Museum no. 35317.

MATERIAL. — MNHN.F.50187 (field number: NAT17-2). Estimated minimal diameter: 25-37 cm.

AGE. — Upper lower to lowermost middle Miocene.

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.

DESCRIPTION

Wood diffuse-porous. Growth rings absent. Vessels solitary (70%) as well as in groups of 2 to 6, evenly distributed ( Fig. 10A ), oval, 0-8 per mm² (average: 3); tangential diameter 85-300 µm (average: 180 µm).Tyloses present ( Fig. 10B ). Vessel elements 130-430 µm (average: 260 µm) long. Perforation plates simple.Intervessel pits alternate, 3-9 µm diameter (mean 6 µm) ( Fig. 10C ). Vessel-ray pits not preserved. Parenchyma paratracheal in vasicentric sheath, broad to aliform with no distinct limit between parenchyma and fibres ( Fig. 10A, B ), maybe diffuse and rarely confluent; parenchyma cells 45-160 µm high (average: 90 µm), 10-45 µm wide (average: 25 µm) in tangential section; 4-8 cells per parenchyma strands. Rays 1- to 6-seriate, mostly 5-seriate ( Fig. 10D, E ), non-storied, 4-7 rays per mm (average: 5), 190-950 µm (average: 480 µm) or up to 50 cells high with end-to-end fusion possible ( Fig. 10E ), 1-seriate and some 2-seriate rays made of upright cells only or mixed with procumbent cells, other multiseriate rays heterocellular made of procumbent cells with 1-4 upright marginal cells ( Fig. 10H ). Some sheath cells present ( Fig. 10E ). Fibres non-septate, 6-30 µm (average: 15 µm) wide, thin-to-thick walled (lumina 1.46 times the double wall thickness) with visible lumen sometimes wide. Radial laticifer tubes present in rays, of the same size as ray cells, visible when filled with black content ( Fig. 10F, G ). In tangential section, much larger or longer cells are visible, with a non-circular shape in the flank of vessels, sometimes even modifying the shape of the rays or between two ray ends ( Fig. 10E ).

DISCUSSION

This specimen is characterized by: 1) diffuse-porous wood; 2) scattered vessels; 3) up to 6-seriate and heterocellular rays, occasionally with sheath cells; 4) diffuse and broad sheath vasicentric to aliform parenchyma; 5) no growth rings; 6) abundant tylose; and 7) radial latificer tubes of the same size as ray cells. These features are characteristic of the Moraceae family ( InsideWood 2004 -onward). Tetramelaceae are also anatomically close but can have growth rings, parenchyma strands or fibres storied, no laticifer tubes and no tyloses ( InsideWood 2004 -onward). Most of the Moraceae genera can be ruled out based upon some diagnostic characters: the presence of septate fibres, banded parenchyma (58% of the specimens described on InsideWood [2004 -onward]), frequent homocellular rays, no diffuse-porous wood, often unilateral parenchyma or almost never sheath cells. One genus is clearly apart from other Moraceae genera because of the absence of any crystal in any type of cells: Artocarpus J.R.Forst. & G.Forst. This feature is also observed in our specimen. Among Artocarpus , 5 species have at least sometimes laticifers according to InsideWood (2004 -onward), and three with sheath cells in addition: A. chama Buch. - Ham. (although it is unclear and varies among publications Pearson & Brown 1932; Purkayastha et al. 1976; Singh et al. 2017), A. dadah Miq. , and A. integer (Thunb.) Merr. (which has no tylosis). According toTer Welle et al. (1986), Artocarpus has common tyloses, non-septate fibres, heterocellular mostly 3-5-seriate rays with 1-2 (5) upright or square marginal cells, sometimes few sheath cells. Parenchyma is mostly aliform, sometimes confluent. Radial latex tube are common, and axial latex tubes can sometimes be present. Singh et al. (2017) described four species of Artocarpus and mention laticifers in A. chama , A. heterophyllus Lam. , A. lamellosus Blanco and A. lacucha Roxb. Ex Buch. -Ham. Unfortunately, the figure does not provide clear illustrations ( Singh et al. 2017: 76, fig. 1). Latex tubes usually appear in radial section as long lines inside rays (which is the case in our fossil) or among fibres, sometimes irregularly crossing both of them; their walls are irregular and the lumina bigger than that of parenchyma cells ( Farías et al. 2009). All of these species are quite similar, and their characters (i.e. non-septate fibres, sheath cells, tyloses, confluent parenchyma and laticifers) seem to vary from authors to others. However, given the descriptions provided in references cited above and figures in InsideWood (2004 -onward), A. chama appears the most anatomically close species to our fossil, as well as A. lacucha and A. lamellosus .

Fossil Moraceae are mainly represented by the genus Ficoxylon Kaiser ( Gregory et al. 2009) which shows mostly banded parenchyma. The fossil genus Artocarpoxylon , also in Moraceae , groups fossils resembling modern Artocarpus ( Prakash & Lalitha 1978) . It displays close similarities with our specimen as it shows no growth rings, mostly solitary vessels, tyloses, vasicentric to aliform parenchyma, 1-6 seriate heterocellular rays and some sheath cells. It also sometimes displays horizontal latex tubes, as in our specimen. Fossil remains related to modern Artocarpus are known as far as the Cretaceous from Asia to North America, Europe and even Greenland ( Ball 1930; Mehrotra et al. 1984; Williams et al. 2017). Two species of this genus are described: A. kartikcherraensis and A. deccanensis Mehrotra, Prakash & Bande ( Mehrotra et al. 1984) . They both have laticifers in rays and strongly resemble our fossil. Artocarpus deccanensis has smaller and more numerous vessels (80-180 µm and 9-20/mm²) and narrower sheath of vasicentric parenchyma than our fossil. Artocarpus kartikcherraensis has vessel diameter and density closer to our fossil (105-315 µm and 2-3/mm²). The present fossil is thus attributed to Artocarpus kartikcherraensis .

Artocarpus is a genus of Asian (also in Pacific and Australia) tropical trees growing in everwet climate or with a short dry season, in evergreen forests or in areas with mild monsoon climate, usually scattered in lowland dipterocarp forests below 1000 m altitude ( Lemmens et al. 1995; Berg et al. 2006). Artocarpus lamellosus lives in evergreen forests, rarely in semideciduous forests or savanna woodlands, commonly found in mixed dipterocarp and sub-montane forests up to 1500 m altitude, on hillsides and ridges ( Lemmens et al. 1995; Berg et al. 2006; Tropical Plants Database 2014 -onward). Artocarpus chama lives in evergreen, semi-evergreen and moist deciduous forests up to 1500 m attitude, in areas with a monsoon climate and rainfall of at least 2000 mm a year ( Gamble 1902; Jarrett 1959). Artocarpus lacucha lives up to 1200-1800m of attitude ( Gamble 1902; Jarrett 1960) in evergreen, semievergreen and moist deciduous forests, with a distinct dry season ( Jarrett 1960).

Figures

FIG. 10. — Artocarpoxylon kartikcherraensis Prakash & Lalitha, MNHN.F.50187: A, Ts, sparse vessels, vasicentric parenchyma sometimes slightly aliform; B: Ts, detail of vasicentric parenchyma and vessels plugged with tyloses; C, Tls, alternate intervessel pits with lenticular appertures; D, Tls,1-6 seriate rays with upright marginal cells; E, Tls, 1-6 seriate rays with sheath cells (black arrow) and end-to-end fusions (white arrow); F, Tls, latex tube in ray, mostly of the same size as ray cells (arrow); G, Rls, view of a latex tube in ray, recognizable as a continuous black line in radial section; H, Rls, heterocellular ray with 1-4 rows of marginal cells, sometimes appearing with upright and procumbent cells mixed due to sheath cells or end-to-end fusions. Scale bars: A, 1 mm; D, 500 µm; B, E, G-H, 200 µm; F, 100 µm; C, 50µm. Abbreviations: see Fig. 2.