First Record of Paraphyllanthoxylon from China

IAWA Journal, Vol. 31 (1), 2010: 89–94

FIRST RECORD OF PARAPHYLLANTHOXYLON FROM CHINA

Xin-Xin Feng 1, Tie-Mei Yi 2* and Jian-Hua Jin1*

SUMMARY A new species, Paraphyllanthoxylon hainanensis, is described from the Eocene Changchang Formation of the Changchang Basin on Hainan Is- land, South China. It is the first record of this genus in China, providing important fossil evidence for research on the phytogeographic history of this genus. The form genus Paraphyllanthoxylon was previously only known from the Cretaceous and Neogene of North America, Mexico, France, Belgium, Japan, India and South Africa. Key words: Eocene, Changchang Formation, Paraphyllanthoxylon, Hainan Island, south China.

INTRODUCTION

So far, about 27 species of Cenozoic angiosperm woods were described from China. All records are from strata of the Neogene and Quaternary (Cheng et al. 2006; Zheng et al. 2008). In this paper a new species, Paraphyllanthoxylon hainanensis, discovered in the Changchang Formation of the Changchang Basin on Hainan Island, south China, is described. The genus Paraphyllanthoxylon was first established by Bailey (1924) to describe angiosperm fossil woods from the Upper Cretaceous of Arizona, USA. In the past 85 years, numerous species of Paraphyllanthoxylon have been described from Cretaceous and Neogene strata of North America (Bailey 1924; Spackman 1948; Cahoon 1972; Thayn et al. 1983; Wheeler et al. 1987; Herendeen 1991; Wheeler 1991; Wheeler et al. 1995; Wheeler & Lehman 2000), Mexico (Martínez-Cabrera et al. 2006), France (Koeniguer 1967; Privé 1975), Belgium (Meijer 2000), Japan (Ogura 1932; Takahashi & Suzuki 2003), India (Ramanujam 1956; Prakash 1958; Prakash et al. 1986), and South Africa (Mädel 1962). Discovery of Paraphyllanthoxylon hainanensis sp. nov. from the Eocene strata of Hainan Island constitutes the first record of this genus in China, providing important fossil evidence for the phytogeographic history of this genus.

MATERIALS AND METHODS

The materials were collected from the coal-bearing series of Changchang Basin (19° 38' 03 N, 110° 27' 04 E) which is located near Jiazi Town, Qiongshan County, in the northern portion of Hainan Island, South China. The coal-bearing series belongs to

1) School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China 2) Beijing Institute of Science and Technology Information, Beijing 100037, China *) Corresponding authors [E-mail: [email protected] (J-H. Jin), [email protected] (T-M. Yi)].

Downloaded from Brill.com09/29/2021 10:00:23AM via free access 90 IAWA Journal, Vol. 31 (1), 2010 the Upper part of the Changchang Formation and is dated as early Eocene–early Late Eocene age (Lei et al. 1992). Four permineralized logs were studied. The structure of the specimens is similar except for some quantitative variations. Samples were prepared for light microscopy by the standard methods of cutting, grinding and polishing us- ing different grades of carborundum powder (Lacey 1963). Anatomical terms used in this paper follow the recommendations of the IAWA list of Microscopic Features for Hardwood Identification (IAWA Committee 1989). Wood identification was based on Anatomy of the Dicotyledons (Metcalfe & Chalk 1950), Woods of China (Cheng et al. 1992), the InsideWood database (http://insidewood.lib.ncsu.edu/search/) and relevant literature. Slides and unsectioned materials are deposited in the Museum of Biology of Sun Yat-sen University, Guangzhou, China.

TAXONOMIC DESCRIPTION

Pa r a p hyllanthoxylon Bailey (1924) Paraphyllanthoxylon hainanensis sp. nov. Holotype: A section of a trunk, 68 cm long and 35 cm in diameter (CCW067). Locality: Hainan Island, South China. Horizon and age: The Changchang Basin, Eocene. Collector: Jian-Hua Jin. Other specimens: HN02, HN03, HN14. Repository: The Museum of Biology of Sun Yat-sen University, Guangzhou, China.

Specific diagnosis Wood diffuse-porous. Growth rings indistinct. Vessels solitary or in radial multiples of 2–4(–5). Tyloses commonly present in vessels. Helical thickenings absent. Perfo- ration plates simple. Intervessel pits alternate, commonly polygonal. Vessel-ray pits variable, regular or irregular, oval, elongated oval, some horizontally elongated. Fibres thin- to thick-walled. Axial parenchyma not observed. Rays uniseriate and multiseriate. Multiseriate ray cells wide, heterocellular. Uniseriate rays rare. Prismatic crystals abundant and present in chambered upright and square ray cells.

Description Wood diffuse-porous. Growth rings indistinct. Vessels commonly in short radial multiples of 2–5 (generally 2–4) and few solitary (Fig. 1A); ratio of solitary pores to pore multiples ranging from 1 : 8 to 1 : 4. Outline of solitary vessels circular to oval. Vessel tangential diameter 81–210 μm, average 133 μm (sd = 18). Vessels 21–28/ mm2, average 24 (n = 6). Tyloses commonly present in vessels. Helical thickenings absent. Perforation plates simple. Intervessel pits alternate, commonly polygonal with circular to elliptic apertures. Vessel-ray pits varying in size; regular or irregular, oval, elongated oval, some horizontally elongated, with large apertures and reduced borders (Fig. 1B). Fibres mostly septate (Fig. 1C), occasionally non-septate, with simple to minutely bordered pits on radial walls. Fibres thin- to thick-walled; wall thickness 2–6.8 μm, average 3.7 μm (sd = 0.49). Axial parenchyma not observed. Rays 5–8

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Figure 1. Paraphyllanthoxylon hainanensis sp. nov. – A: Transverse section, showing diffuse- porous wood; indistinct growth rings; vessels commonly in short radial multiples; tyloses present in vessels. – B: Radial section, showing vessel-ray pits. – C: Tangential section, showing septate fibres. – D: Tangential section, showing long uniseriate extensions of the multiseriate rays. – E: Radial section, showing rays heterocellular. – F: Radial section, showing crystals present in upright ray cells. — Scale bars: A, D, E = 25 μm; B, C, F = 50 μm. per mm, uniseriate and multiseriate. Multiseriate rays 2–4 (occasionally 5) cells wide (Fig. 1D), heterocellular (Fig. 1E), composed of procumbent cells with 1–14 (mostly 1–6) rows of square to upright marginal cells, and upright cells occasionally also present in the middle part of multiseriate rays. Uniseriate rays rare. Vertical fusions common with uniseriate and multiseriate portions alternating. Prismatic crystals abundant and present in chambered upright (Fig. 1F) and square ray cells.

DISCUSSION

The genus Paraphyllanthoxylon was first described by Bailey (1924) with the following combination of features: indistinct well-defined growth rings; diffuse-porous wood; solitary or radially grouped vessels; simple perforation plates; abundant tyloses; septate fibres and heterocellular multi–uniseriate rays. Although Bailey (1924) proposed this name to show its similarity to the genera Bridelia and Phyllanthus of the section

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Phyllanthoideae of the Euphorbiaceae, the characters listed above are common to a number of extant families, including Anacardiaceae, Burseraceae, Elaeocarpaceae, Euphorbiaceae, Flacourtiaceae, Lauraceae, and Violaceae (Wheeler et al. 1987). Con- sequently, the systematic position of this genus remains uncertain. While some research- ers maintain that it is not proper to assign this genus to Euphorbiaceae because of its similarity to other families (Bailey 1924; Spackman 1948; Cahoon 1972; Wheeler 1991), the majority of authors emphasize its affinity with Euphorbiaceae (Mädel 1962; Privé 1975; Thayn et al. 1983; Thayn & Tidwell 1984; Prakash et al. 1986). According to the occurrence and number of marginal rows on multiseriate rays and the amount of the uniseriate rays, Wheeler et al. (1987) and Herendeen (1991) divided this genus into two anatomical groups: Group I: Those species with few, short marginal extensions on the multiseriate rays and few or rare uniseriate rays, such as P. alabamense, P. capense, P. idahoense, P. marylandese, and P. utahense. These show greater affinity with Lauraceae, Elaeocarpaceae, Anacardiaceae, Burseraceae, and Verbenaceae. Group II: Those species with abundant uniseriate rays and long uniseriate extensions on the multiseriate rays, such as P. arizonense and P. illinoisense. These are more similar to species of Ulmaceae, Flacourtiaceae, Euphorbiaceae, and Simaroubaceae. After comparison with all reported species of Paraphyllanthoxylon, the studied wood resembles P. arizonense and P. illinoisense more than the others in its combination of features. However, it can be distinguished from these two species in the following features: vessel-ray pits are not markedly larger than intervessel pits in P. arizonense while vessel-ray pits are large, varying in size, regular or irregular in P. hainanensis; rays of P. illinoisense tend to be of two sizes, an outstanding feature not occurring in the studied wood. Therefore, a new species is justified. Paraphyllanthoxylon has characteristics of the Euphorbiaceae, but these features also occur in other families (Wheeler 1987; Herendeen 1991). After comparison of our fossil species with those extant families, the closest anatomical similarity is found with members of Euphorbiaceae and Flacourtiaceae, both of which exhibit a combination of septate fibres, heterocellular rays, multiseriate rays with large uniseriate extensions, absence of axial parenchyma (or scanty paratracheal), simple perforation plates, alternate intervessel pits, and large vessel-ray pits. We concur with Bailey’s original intent, and Cahoon’s as well as Spackman’s remarks about the affinities ofParaphyllanthoxylon , i.e. although similar to the phyllanthoid Euphorbiaceae, Paraphyllanthoxylon cannot be assigned with certainty to the Euphorbiaceae because of its similarities shared with other families (Metcalfe & Chalk 1950). In Flacourtiaceae, uniseriate rays are numerous and composed of high upright cells (Metcalfe & Chalk 1950). Furthermore, the representative feature of Paraphyllanthoxy- lon hainanensis, prismatic crystals existing in upright ray cells, only occurs in Ahernia, Hasseltia, Homalium, Scolopia of Flacourtiaceae (Wheeler & Manchester 2002). Of the four genera, some scalariform perforation plates exist in Ahernia and Homalium; intervessel pitting appears scalariform in Hasseltia; the vessel to ray pitting of Scolopia is small and quite similar to its intervessel pitting (Metcalfe & Chalk 1950). All three features are lacking in Paraphyllanthoxylon hainanensis. Consequently, it seems inap- propriate to place P. hainanensis in Flacourtiaceae.

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The large family Euphorbiaceae includes a great number of woody taxa. Great similarity exists between P. hainanensis and the woods of some genera in the Glochidion group of the Euphorbiaceae, subfamily Phyllanthoideae, such as subtribe Flueggeinae, Antidesma, Bischofia, Bridelia, Hymenocardia, Neowawrea, Spondiathus, and Uapaca, and due to features of simple perforation plate and medium to large vessel-ray pitting (Mennega 1987). The non-septate fibres inUapaca and thin-walled fibres inBischofia exclude their similarities with P. hainanensis. In summary, the Hainan Paraphyllan- thoxylon morphospecies shares the greatest anatomical resemblance to Antidesma, Bridelia, Hymenocardia, Neowawrea, Spondiathus, and subtribe Flueggeinae, all in the Euphorbiaceae.

ACKNOWLEDGEMENTS

This study was supported by the National Natural Science Foundation of China (No. 40672017), the NSFC-RFBR project (No. 40811120033 and No. 07–04–92127), the key project of the Ministry of Education of China inviting foreign teachers, the Guangdong Provincial Natural Science Foundation of China (No. 06023161), and the Scientific Research Fund, Hongda Zhang, Sun Yat-sen University. Graduate students majoring in Plant Science at Sun Yat-sen University participated in the field col- lection of the fossils. We also thank Ms. Margaret Joyner, University of Florida, and Dr. Xin Wang, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences for improving the manuscript.

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