IAWA Journal, Vol. 33 (2), 2012: 197–204 A NEW SPECIES OF PISTACIOXYLON (ANACARDIACEAE) FROM THE MIOCENE OF YUNNAN, CHINA Ye-Ming Cheng1,*, R.C. Mehrotra2, Yue-Gao Jin1, Wei Yang1 and Cheng-Sen Li3,* SUMMARY A new species of Pistacioxylon, Pistacioxylon leilaoensis Cheng et al., showing affinities withPistacia of the Anacardiaceae is described from the Miocene of Leilao, Yuanmou Basin, Yunnan Province, southwest China. It provides data for reconstructing the phytogeographic history of Pistacia and the paleoenvironment of the Yuanmou Basin. This fossil suggests a long history of exchange of various taxa including Pistacia between Europe and East Asia during the Tertiary. Key words: Pistacia, fossil wood, phytogeography, Xiaohe Formation, Southwest China. INTRODUCTION The Yuanmou Basin of Yunnan Province, southwest China, is well known for its Yuanmou Man (Homo erectus) (Qian 1985) and hominoid fauna fossils (He 1997). Abundant hominoid and mammal fossils have been reported since 1980 from the Late Miocene Xiaohe Formation of Leilao and Xiaohe, Yuanmou Basin, Yunnan (Pan & Zong 1991; He 1997; Harrison et al. 2002; Liu & Pan 2003; Yue et al. 2003; Qi et al. 2006). The age and character of the Xiaohe fauna are similar to those of the Late Miocene Siwalik fauna of Pakistan (Pan & Zong 1991). The Yuanmou Basin might have been an important refuge for hominoids when they became extinct in the rest of Eurasia (Zhu et al. 2005). The Late Miocene Xiaohe Formation of Leilao, Yuanmou Basin, also contains fossil woods (Zhang et al. 2002) and their study can provide important information for the reconstruction of the paleoenvironment of the basin. The present study describes a new species of Pistacioxylon, a wood with features seen in Pistacia (Anacardiaceae) from the Late Miocene of Yuanmou, Yunnan, China, and gives light on the phytogeographic history of the genus. MATERIALS AND METHODS The material for the present study was collected from the hominoid fossil site of Leilao Village, Yuanmou County, Yunnan Province, southwest China. The sediments from 1) The Geological Museum of China, Beijing 100034, China. 2) Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226007, India. 3) State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China. *) Corresponding authors [E-mail: [email protected]; [email protected]]. Downloaded from Brill.com10/01/2021 10:18:24AM via free access 198 IAWA Journal, Vol. 33 (2), 2012 Downloaded from Brill.com10/01/2021 10:18:24AM via free access Ye-Ming Cheng et al. — A new species of Pistacioxylon 199 which the fossil wood was derived belong to the Late Miocene Xiaohe Formation which is dated as 7.2–8.1 Ma based on paleomagnetic evidence (Qi et al. 2006). The specimen studied is about 10 cm in length. The slides were prepared accord- ing to the standard methods of cutting, grinding and polishing using different grades of carborundum powder (Lacey 1963). Both specimen and slides are deposited in the Geological Museum of China. Anatomical terms used in this paper follow the recom- mendations of the IAWA list of microscopic features for hardwood identification (IAWA Committee 1989). SYSTEMATIC DESCRIPTION Family Anacardiaceae Genus PISTACIOXYLON Dupéron (1973) Species Pistacioxylon leilaoensis Cheng, Mehrotra, Jin, Yang & Li, spec. nov. (Fig. 1) Specific diagnosis Growth rings distinct. Wood ring-porous. Vessels in earlywood mainly solitary, few in radial pairs, latewood vessels in long radial multiples or clusters. Perforation plates simple. Intervessel pits alternate, round to polygonal. Helical thickening present in narrow vessels. Vessel-ray pits not visible. Tyloses common, thin-walled. Axial parenchyma sparse. Rays 1–7-seriate, mostly 4–5-seriate, heterocellular, composed of procumbent cells with 1(–2) rows of square or upright marginal cells; radial canals present in some rays. Description Growth rings distinct, marked by the earlywood and latewood vessel diameter and distribution and flattened fibers. Wood ring-porous. Vessels in earlywood mainly solitary, few in radial pairs, circular to oval in cross section, mean tangential diameter of solitary vessels 170 µm, range 109–265 µm, radial diameter 147–261 µm. Latewood vessels in long radial multiples or clusters. Perforation plates simple. Intervessel pits alternate, round to polygonal, 5–8 µm in diameter. Helical thickenings present in narrow vessels. Vessel-ray pits not visible due to poor preservation. Tyloses common, thin-walled. Axial parenchyma sparse, scanty paratracheal. Rays 5–8/mm, 1–7-seriate, 1–2-seriate rays very few, mostly 4–5-seriate rays, mul- tiseriate rays 7–38 cells or 181–599 µm high, heterocellular, composed of procumbent body cells with 1(–2) rows of square or upright marginal cells; radial canals occasionally present. ← Figure 1. Pistacioxylon leilaoensis Cheng et al., sp. nov. (Anacardiaceae) (P2290). – A: Cross section showing distinct growth rings and ring-porous wood. – B: Cross section showing vessels predominantly solitary in earlywood and mostly in radial multiples and clusters in latewood. – C: Tangential section showing alternate intervessel pits. – D: Vessel elements with helical thickenings. – E: Radial section showing heterocellular rays. – F: Tangential section showing distribution of rays. – G: Tangential section showing structure of rays and radial canal. — Scale bars: A = 1 mm; B, F = 200 μm; C = 20 μm; D = 50 μm; E, G = 100 μm. Downloaded from Brill.com10/01/2021 10:18:24AM via free access 200 IAWA Journal, Vol. 33 (2), 2012 Holotype: P2290, a specimen 10 cm long. Locality: Leilao Village, Yuanmou County, Yunnan Province, China. Horizon: Xiaohe Formation. Age: Late Miocene. Repository: Geological Museum of China, Beijing, China. DISCUSSION Comparison with extant woods The fossil is characterized by ring-porous wood with distinct growth rings, thin- walled tyloses, latewood pores mainly in radial multiples and clusters, simple perfo- ration plates, alternate intervessel pits, narrow vessels with helical thickening, sparse axial parenchyma, heterocellular rays and radial canals. This combination of characters occurs in woods of Pistacia, Rhus and Schinus of the Anacardiaceae (Metcalfe & Chalk 1950; Ghosh & Purkayastha 1963; Ilic 1991; Cheng et al. 1992; InsideWood 2004-onwards). Both Pistacia and Rhus occur in Asia and possess helical thickenings in narrow vessels and radial canals in rays (Cheng et al. 1992; Dong & Baas 1993; Gupta & Agarwal 2008). Ring-porous Pistacia are characterized by a narrow earlywood zone, latewood with radially as well as obliquely arranged long radial multiples and vessel clusters, and radial canals are common. In contrast, ring-porous species of Rhus have a wide earlywood with several rows of vessels, and radial canals are only occasional (Heimsch 1940; Fahn et al. 1986; Young 1974; Détienne & Jacquet 1983; Fahn et al. 1986; Schweingruber 1990; Cheng et al. 1992; Dong & Baas 1993; Gupta & Agarwal 2008; InsideWood 2004-onwards). The species of Schinus native to South America mostly have diffuse wood and narrow rays (1–3-seriate, InsideWood 2004-onwards). The present fossil wood shows maximum similarities with Pistacia. Pistacia, a small genus of trees and shrubs, is better known for its fruits and gums than for timber. It contains nine species that are native to Eurasia from the Mediterranean region eastward to India, China and the Philippines, as well as the southern U.S.A. and Mexico (Min 1980; Mabberley 2008). The species of Pistacia in the Mediterra- nean region grow mainly in dry areas (Min 1980). Most of the species of this genus have ring-porous wood (Schweingruber 1990; Cheng et al. 1992; Dong & Baas 1993; Selmeier 2000; Gupta & Agarwal 2008; InsideWood 2004-onwards), but some have diffuse-porous wood. The present fossil wood is similar to those species having ring porosity, one row of earlywood pores and rays that are 3–5-seriate, such as Pistacia atlantica Desf. (Fahn et al. 1986, p. 63-64, plate 7A-C; Schweingruber 1990, p. 188, fig. 6–10), P. chinensis Bunge (Fig. 2) and P. terebinthus L. (Schweingruber 1990, p. 188, fig. 1–5). Two species of Pistacia, namely P. weinmannifolia J. Poisson ex Franch. and P. chinensis Bunge are widely distributed in China, except in Inner Mon- golia and Northeastern China (Zheng & Min 1980). The former possesses diffuse- porous wood and grows in forests or shrub dominated areas of limestone mountains at elevations of 580–2700 m in Yunnan, Xizang, Sichuan, Guizhou and Guangxi, while the latter has ring-porous wood and is distributed in montane forests at elevations of 140–3550 m in southward Yangtze River, northern and northwestern China. Downloaded from Brill.com10/01/2021 10:18:24AM via free access Ye-Ming Cheng et al. — A new species of Pistacioxylon 201 Figure 2. Extant Pistacia chinensis Bunge (Anacardiaceae) (CAFw8636, Sichuan, southwest- ern China). – A: Cross section showing distinct growth rings and ring-porous wood, vessels predominantly solitary in earlywood and mostly in radial multiples and clusters in latewood. – B: Radial section showing heterocellular rays, simple perforation plate and vessel elements with helical thickenings. – C: Tangential section showing structure of rays, radial canal and thin-walled tyloses. — Scale bars: A, C = 200 µm; B = 100 µm. Comparison with fossil woods Dupéron (1973) established the genus Pistacioxylon based on the comparison of fossil woods with woods of extant Pistacia. Four species of Pistacioxylon described so far are: P. muticoides Dupéron from the Oligocene Molassic Formation of southwest France (Dupéron 1973), P. holleisii Selmeier (2000) from the Late Miocene of Bavaria, Germany, P. praeterebinthus Gottwald and Pistacioxylon sp. from the Miocene (?) of Bavaria, Germany (Gottwald 2004). Pistacioxylon holleisii distinctly differs from the Chinese specimen in having 1–3-seriate rays and an earlywood with 4 rows of pores; P. praeterebinthus and Pistacioxylon sp. can be distinguished from our specimen in having multiple rows of earlywood pores; P. muticoides is similar to this Chinese wood in having only one row of earlywood pores, but differs in having narrower (mostly 1–3- seriate) rays.