Itaquixylon heterogenum BENICIO, PIRES, DA ROSA, SPIEKERMANN, UHL et JASPER, 2016

Benicio, Jose R. W., Pires, Etiene F., Da Rosa, Átila A. S., Spiekermann, Rafael, Uhl, Dieter & Jasper, André, 2016, A New Fossil Fabaceae Wood From The Pleistocene Touro Passo Formation Of Rio Grande Do Sul, Brazil, Fossil Imprint 72 (3 - 4), pp. 251-264 : 254

Itaquixylon heterogenum BENICIO, PIRES, DA ROSA, SPIEKERMANN, UHL et JASPER sp. nov.

H o l o t y p e. UFSM 12032 (Repository: Coleção Paleontológica da Universidade Federal de Santa Maria, Rio Grande do Sul, Brazil).

E t y m o l o g y. The specific name, heterogenum , is due to the presence of heterocellular rays.

T y p e h o r i z o n. Touro Passo Formation.

A g e. Late Pleistocene, 14,600 years (TL).

T y p e l o c a l i t y. (29º23'55.9"S / 56º42'05.9"W), Itaqui city, Rio Grande do Sul State, Brazil .

D i a g n o s i s. Angiosperm wood, diffuse porosity, numerous vessels in tangential bands; vessels generally solitary, sometimes in radial multiples of 3 to 5, circular to oval in outline, with narrow diameter and short length, helical thickenings absent, tyloses present; simple perforation plates; alternate intervessel pits, vestured, circular, small with lenticular irregular aperture slightly oblique; vessel-ray pits and vessel-parenchyma pits bordered; libriform fibres, non-septate, extremely short and narrow, with simple minute pits; paratracheal axial parenchyma, vasicentric and scanty and apotracheal axial parenchyma diffuse; rays are nume. rous, exclusively heterocellular, composed of procumbent and square marginal cells, short and extremely narrow, simple pits of minute size; mostly uniseriate, less frequently biseriate and triseriate, rarely tetraseriate; aggregate rays are absent.

D e s c r i p t i o n. Distinctive growth rings, alternately separated by light and dark bands (Pl. 1, Fig. 1), marked by radially flattened thick-walled latewood fibres versus thin-walled earlywood fibers. Absence of stratification in secondary xylem elements. Wood diffuse-porous (Pl. 1, Figs 1–2). Vessels in tangential bands (Pl. 1, Figs 1–2), numerous (16–36/mm²), occupying 25.6% of the cross section (Pl. 1, Figs 1–2). Vessels generally solitary, sometimes in radial multiples of 3 to 5, circular to oval in outline (Pl. 1, Figs 2–3). Mean tangential diameter 65.5 (32–96) µm, mean length 186.5 (48–360) µm. Helical thickenings in vessel elements are absent. Simple perforation plates (Pl. 2, Fig. 4), intervessel pits alternate, small 4.1 (2–8) µm, vestured, with lenticular irregular slightly oblique apertures (Pl. 1, Figs 4–5). Vessel-ray pits with distinct borders, rounded and bordered (Pl. 1, Figs 4–5). Vessel-parenchyma pits are similar to vessel-ray pits. Tyloses (Pl. 1, Figs 2–6) and prismatic crystals are present in the marginal square ray cells (Pl. 2, Figs 4–6). Fibres libriform, non-septate, with simple and minutely bordered pits 2.3 (1–4) µm (Pl. 2, Figs 1–4), occupying 45% of the wood. The fibres are extremely short, mean length 162 (30–360) µm, narrow 3.2 (1–8) µm and thin-walled 1.9 (1–4) µm, with a narrow diameter of 3.9 (2–8) µm. The paratracheal axial parenchyma is vasicentric and scanty, occupying only 5.45% of total wood volume (Pl. 1, Figs 2–3). The apotracheal axial parenchyma is diffuse, with dispersed cells between the fibers (Pl. 1, Fig. 2–3). Axial parenchyma cells are rectangular (Pl. 2, Fig. 2), mean length 36.9 (16–80) µm and mean width 18.5 (8–32) µm, constituting a series with mean length 364.8 (176–896) µm, composed of 13 (3–6) cells. Rays are numerous, occupying 24% of the volume of the wood (Pl. 1, Figs 1–2). They are mostly uniseriate (44%), less frequent biseriate (27%), triseriate (21%) and tetraseriate (8%) (Pl. 2, Figs 1–3). Aggregate rays are absent. Rays are heterocellular, composed of procumbent cells and 1–4 rows of square marginal cells, most commonly 2 rows (Pl. 2, Figs 4–5). Uniseriate rays extremely short, mean length 204.9 (112–424) µm, and extremely narrow, mean width 12.4 (8–24) µm, 7 to 27 cells high (Pl. 2, Figs 1–3). The multiseriate rays are narrow, mean width 26.8 (16–40) µm, 1 to 4 cells wide, and very short, mean length 241.5 (120–556) µm, 8 to 27 cells high (Pl. 2, Figs 1–3). In tangential section, the ray cells are circular to oval (Pl. 2, Figs 1–3) with minute simple pits, ranging from 1 to 4 µm.