Cupressinoxylon sp.

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 : 856-858

Cupressinoxylon sp.

( Fig. 2 )

MATERIAL. — MNHN.F.50171 (field number: 17FN15). Estimated minimal diameter: 15-25 cm.

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar

AGE. — Upper lower to lowermost middle Miocene

DESCRIPTION

Growth ring boundaries distinct ( Fig. 2A ), marked by 1-5 lines of flattened tracheids ( Fig. 2B ). Transition from earlywood to latewood gradual or indistinguishable due to flattening. Tracheids 2100-3200 µm long (average 2730 µm, n=20), tangential diameter 20-50 µm (average 30 µm), thin walled with polygonal cross-section. Radial pits 1-seriate, rounded, spaced, 15-24 µm in diameter (average: 21 µm) ( Fig. 2H ). Tangential pits present, minute to small ( Fig. 2F ). Axial parenchyma diffuse and zonate in the vicinity of growth ring boundaries ( Fig. 2A, C ), both horizontal and vertical walls smooth ( Fig. 2E ), 17-33 µm tangential diameter (average: 25 µm). Rays 1- to 2-seriate, biseriate parts are present here and there (K 10 %), only composed of parenchyma cells, 3-22 cells high (average: 8) ( Fig. 2C, D ); ray cells 13-30 µm in tangential diameter (average: 30 µm), both vertical and horizontal walls smooth ( Fig. 2I ), indentures not visible. Cross-field pits possibly cupressoid or podocarpoid, maybe both, seemingly 2-4 pits per cross-field ( Fig. 2G ); 6-15 µm in diameter (average: 11 µm). Crystals not found. Resin canals absent.

DISCUSSION

This specimen of homoxylate wood is characterized by: 1) tracheids with a polygonal transverse section; 2) uniseriate and spaced tracheid pits; 3) 1- to 2-seriate and rather short rays; 4) presence of tangential pits; and 5) smooth axial parenchyma and ray cell walls. It is thus attributed to conifers. The presence of axial parenchyma is reported in Podocarpaceae and Cupressaceae (including Taxodiaceae ). According to Greguss (1955, 1972), Trivedi & Srivastava (1989) and the IAWA Committee (2004), zonate axial parenchyma is more frequent in Cupressaceae but is not completely diagnostic. It is yet a diagnostic feature of Cupressaceae when it includes dark content in the transverse section and in the transverse end walls of parenchyma cells in longitudinal sections, which is the case for our specimen.

Wood species of the cupressoid group are poorly distinguishable from each other based on wood anatomy alone ( Phillips 1948; Wheeler & Dillhoff 2009). Kress et al. (2003) record 23 species of Cupressaceae (most of them are non-native) in Myanmar, including Cryptomeria D. Don which shares common traits with our specimen, especially uni- to biseriate rays and Libocedrus Endl. ( Greguss 1972) .

Within theInsideWood (2004-onward) database, Chamaecyparis formosensis Matsumura and Taxodium distichum (L.) Rich. match partially with our sample (InsideWood input code: 44p 61a 72p 73p 74p 80p 98p 99p 103p 108p). With less restrictive searches (e.g., excluding criteria such as smooth cell wall, cross-field pits cupressoid or podocarpoid and / or ray width from 1- to 2-seriate) most taxa still belong to Cupressaceae ( Chamaecyparis Spach. , Cupressus L., Juniperus L.). However, no clear modern relative among modern Cupressaceae can be found for this fossil. Nonetheless, our specimen shares all the diagnostic features of the fossil genus Cupressinoxylon (cross-field pits oblique and more or less narrow, ray walls mostly smooth, parenchyma often present, resin ducts absent), which are wide enough to include most of Cupressaceae species ( Vaudois & Privé 1971). The poorly preserved cell walls and the relatively small size of our specimen makes it difficult to determine the affinity at the species level. Wheeler & Dillhoff (2009) also note that “there are more species of Cupressinoxylon than there are distinctive wood anatomical types within extant Cupressaceae ” ( Wheeler & Dillhoff 2009: 84).

Cupressaceae are mainly mesic-hydric (from balanced hydric conditions to wet conditions) trees in temperate or seasonal climates ( Wilf et al. 2009; Pittermann et al. 2012) and all kinds of climate adaptation can be found in this pangeographic family, from moist tolerant trees to very drought-tolerant ( Pittermann et al. 2012). Today, few species of Asian and Western-Pacific Cupressaceae grow in tropical areas from lowlands (600 m) to tree line: Papuacedrus H.L.Li , some Calocedrus Kurz and Libocedrus ( De Laubenfels 1988; Earle 2004 -onward). They are found in the tropics above 600 m of elevation, but few species occur in lowland tropical areas (<600m): Libocedrus yateensis Guillaumin and Callitris pancheri (Carrière) Byng from New-Caledonia, Callitris macleayana (F.Muell.) F.Muell. from Australia or Glyptostrobus pensilis (Staunton ex D.Don) K.Koch in China and Southeast Asia ( Farjon 2005).

Figures

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.