Vol. 7, No. 2, p. 157161, June 2003
Comparison of Korean and Japanese Tertiary fossil wood floras with special references to the genus Wataria
ABSTRACT: Among 64 fossil woods collected from the Upper Coal-bearing Formation of Janggi Group, Pohang, Korea, four specimens have been characterized by their distinct ring porosity and the presence of tile cells in rays. After detailed anatomical studies, we could identify them as two species of Wataria--W.
miocenica and W. parvipora. Genus Wataria, known as an extinct taxon of Sterculiaceae, has been found only in the Tertiary for- mations in Japan. Most of these sterculiaceous plants are thermo- philic and reportedly never inhabited in the Korean Peninsula.
The existence of fossil woods of Wataria in Korea supports the idea of a common flora established in both countries during the Ter- tiary. In Japan, fossil woods of Wataria have been found only dur- ing the early Miocene formations. Therefore, the age of the Upper Coal-bearing Formation can be said of as the early Miocene.
Key words: fossil wood, genus Wataria, Japan, Korea, Tertiary
1. INTRODUCTION
The Tertiary period lasted for a total of 63 million years, stretching from 65 million years ago to 1.8 million years ago and ended with the beginning of the Quaternary period.
The flowering plants, which must have originated during the Upper Jurassic (Sun et al., 1998), became dominant ter- restrial plants during the Tertiary (Stewart and Rothwell, 1993). In particular, there are abundant residual taxa of the Tertiary plants in Northeast Asian regions, including Korean Peninsula, Japan and northeastern China. Therefore, the Tertiary is a very important geologic period in revealing the origin and evolution of the extant flora in Northeast Asia.
The opening of East Sea (or also called Sea of Japan) and the separation of Japanese archipelagos from the East Asian Continent seemed to happen at the end of Oligocene or Lower Miocene (Lallemand and Jolivet, 1985). Korean Peninsula was linked with some of Japanese islands during most of the Tertiary period and both areas are assumed to have constituted a common flora. After two areas separated from each other, the evolution of plants in both areas occurred independently. Therefore, the comparison of Tertiary fossil plants in Korea and Japan will give us valuable information on the origin and evolution of plants in both areas.
A variety of plant organs can be a fossil plants. We chose fossil woods among them as a subject of our studies because they have some advantages as follows.
1) Wood is hard and quite stable in structure. These char- acteristics help maintaining its fine anatomical structure in the fossil. 2) Wood is composed of many kinds of tissues and cells with various arrangements. Therefore, wood could provide us lots of anatomical information to help identify plant species exactly (Barefoot and Hankins, 1982).
There are several Tertiary basins scattered sporadically along the eastern coast of Korea, namely Bukpyong, Yang- hae, Pohang, Eoil and Ulsan. Among them, the Pohang basin is the widest and has produced the most abundant fos- sils. Therefore, many geological and palaeontological atten- tions have been paid to the Pohang basin (Tateiwa, 1924;
Um and Yu, 1966; Huzioka, 1972; Takahashi and Kim, 1979; Paik et al., 1979; Bong, 1981; Chun, 1982; Park, 1995).
The so-called green-tuff deposition of the Tertiary period is widely distributed around the Pohang basin. Because the green-tuff often contains lots of fossil woods, it is also known that the Tertiary formations in the Pohang basin have produced abundant fossil woods. However, there was no palaeobotanic attention given to them.
In Japan, the green-tuff is found from the northern end of Hokkaido Island to the western coast of Honshu Island. The fossil woods found in many localities have been subjects of many studies since the early 20 th century. Those studies revealed the full diversity in wooden flora in the Tertiary and the floral changes in accordance with the climatic change in the geological time (Tanai, 1961; Suzuki, 1985;
Suzuki and Hiraya, 1989).
Due to scarcity of Korean researchers interested in fossil woods, we have limited information about the occurrence and locality of fossil woods in Korea. The existence of the deposition identical to Japanese green-tuff which bears a huge amount of fossil woods indicates that a large amount of fossil woods will also exist under the identical deposition in Korea. Therefore, it is evident that the study of fossil woods will be important to explain the evolution of plants as well as the floras of Korea and Japan.
The fossil woods of Wataria have been found from the Eun Kyoung Jeong*
Kyungsik Kim Jong Heon Kim Mitsuo Suzuki
Department of Biology, Graduate School of Chonbuk National University, Chonju 561-756, Korea Faculty of Biological Sciences, Chonbuk National University, Chonju 561-756, Korea
Department of Earth Science Education, Kongju National University, Kongju 314-701, Korea Botanical Garden, Graduate School of Science, Tohoku University, Kawauchi, Aoba, Sendai 980, Japan
*Corresponding author: [email protected]
woods found both in Korean Peninsula and Japanese Islands.
2. MATERIALS AND METHODS
The Pohang Basin is the largest one which is divided into two groups, Yeonil and Janggi Groups (Lee et al., 1992;
Park, 1995). However, the two groups could be regarded as independent isolated basin (Kim, 1970). The Janggi Gropup is divided into acidic volcanic rock, Janggi Conglomerate, Nuldaeri Trachyte Tuff, Geumgwangdong Shale, Lower Coal-bearing Formation, Lower Basaltic Tuff, Upper Coal- bearing Formation, Geumori Andesitic Tuff, Upper Basaltic Tuff in ascending stratigraphical order (Tateiwa, 1924; Park, 1995) (Table 1). There are some inconsistencies in presum- ing which age Janggi fossils belong to. Based on the flora of fossil leaves, Huzioka (1972) supposed that they belong to the Early Miocene. Meanwhile, Tateiwa (1924) and Chun (1982) supposed that they come from the Oligocene.
64 fossil woods were collected from the Upper Coal- bearing Formation of Janggi Group, Pohang, Korea from August 1999 to March 2001 (Fig. 1). All fossil specimens
examined are silicified woods. Ground cross, tangential and radial thin sections were prepared in accordance with con- ventional techniques. All the microscope slides examined in this paper are deposited in the Fossil Wood Collection of the Herbarium, Faculty of Biological Sciences, Chonbuk National University, Chonju, Korea.
3. RESULTS
Among the 64 fossil woods were collected from the Upper Coal-bearing Formation of Janggi Group, Pohang, Korea, four specimens were identified as the genus Wataria, one of them as W. miocenica (KNU 0010) and three of them as W.
parvipora (KNU 0008, 0019, 0044). The anatomical fea- tures of Wataria species from Pohang basin are summarized in Table 2 and described as follows.
Family Sterculiaceae
Genus Wataria Terada et Suzuki
Wataria miocenica (Watari) Terada et Suzuki (Figs. 2−5) in Terada et Suzuki, 1998. Rev. Palaeobot. Palynol., 103: 238.
Table 1. Stratigraphic of the Janggi Group (Tateiwa, 1924; Park, 1995).
Tateiwa (1924)
Janggi Group (Early Miocene) Upper Basaltic Tuff Geumori Andesiti Tuff Upper Coal-bearing Fm.
Lower Basaltic Tuff Lower Coal-bearing Fm.
Geumgwangdon Shale Nuldaeri Trachyte Tuff Janggi Comglomerate acidic volcanic rock
Fig. 1. Simplified geologic map of the studied area (Park, 1995) and sampling locality (Star indicates sampling site).
Table 2. Some representative anatomical characters of the Wataria from Korea.
Species Wide vessels in earlywood Narrow vessels in latewood Rays
TDa(µm) RDa(µm) LV NV WT(µm) HTb MRHa(µm) MRWa(µm) TT
W. miocenica 195−325 (252) 205−324 (268) 1−3 solitary 8.5 − 140−1900 (985) 30−125 (84) I W. parvipora 125−250 (181) 126−276 (201) 1−3 solitary 7.3 − 120−900 (558)0 25−115 (67) I TD=tangential vessel diameter, RD=radial vessel diameter, LV=layers of wide vessels in earlywood, NV=narrow vessels, WT=mean wall thickness of narrow vessel, HT=helical thickenings on vessels walls, MRH=multiseriate ray height, MRW=multiseriate ray width, TT=type of tile cells; I=intermediate of Durio- and Pterospermum-types, aRange (mean). b− =absent; +=present.
Reevesia miocenica Watari
in Watari, 1952. J. Fac. Sci. Univ. Tokyo Sect. III (Bot- any), 6: 116−129, photos. 8C−D, 9A−E.
Suzuki et Watari, 1994. J. Plant Res., 107: 71.
Material: KNU 0010
Description: Wood distinctly ring porous with wide ves- sels in earlywood and narrow vessels in latewood. Growth rings distinct; 0.4−3 mm wide.
Wide vessels mostly solitary and round in cross section;
arranged one to three layers in earlywood; 195−325 (mean 252)×205−324 (mean 268) µm in tangential×radial diame- ter. Narrow vessels mostly solitary and round in cross sec- tion; forming 2−5 groups; walls thick (about 8.5µm); helical thickenings absent.
Vessel elements short, 200−345 (mean 257) µm long;
perforation plates exclusively simple; intertracheary pitting
alternate; rarely gum-like deposit observed; helical thicken- ings absent.
Fiber consisting ground mass of the latewood with axial parenchyma; square and polygonal in cross section.
Axial parenchyma apotracheal and paratracheal; fusiform and strands of 2−10 cells or more; storied structure. Apo- tracheal parenchyma uni- or biseriate tangential bands in latewood. Paratracheal parenchyma vasicentric around wide vessels and narrow vessels. Crystals absent.
Rays heterocellular. Multiseriate rays 140−1900 (mean 985) µm tall and 30−125 (mean 84) µm wide; composed of tile cells and procumbent cells. Tile cells 15.2−24.7 (mean 19.7)×19−34.2 (mean 23.5)×9.5−13.3 (mean 11.7) µm in tangential×vertical×radial diameters. Procumbent cells 9.5−
13.3 (mean 11.7)×9.5−15.2 (mean 12.5)×38−76 (mean 55.1) µm in tangential×vertical×radial diameters. Rarely crystals present.
Figs. 2−5. Microphotographs of Wataria miocenica (KNU 0010).
Fig. 2. Cross section showing distinct ring porous. Fig. 3. Cross section showing narrow vessels in latewood. Fig. 4. Radial section showing tile cells and procumbent cells. Fig. 5. Tangential section showing uniseriate and multiseriate rays with tile cells, and storied structure of axial parenchyma (Scale bars=100µm; WV=wide vessels;
NV=narrow vessels; TC=tile cells; UR=uniseriate rays; MR=
multiseriate rays).
Figs. 6−9. Microphotographs of Wataria parvipora (KNU 0010).
Fig. 6. Cross section showing distinct ring porous. Fig. 7. Radial section showing tile cells and procumbent cells. Fig. 8. Radial sec- tion showing wide vessel with alternate pitting. Fig. 9. Tangential section showing uniseriate rays and multiseriate rays and storied structure (Scale bars=100µm; WV=wide vessels; NV=narrow ves- sels; TC=tile cells; UR=uniseriate rays; MR=multiseriate rays).
181)×126−276 (mean 201) µm in tangential×radial diame- ter. Narrow vessels mostly solitary and round in cross sec- tion; forming 2−5 groups; walls thick (about 7.3µm); helical thickening absent.
Vessel elements short, 125−250 (mean 178) µm long;
perforation plates exclusively simple; intertracheary pitting alternate; rarely gum-like deposit observed; helical thicken- ing absent.
Fiber consisting ground mass of the latewood with axial parenchyma; square and polygonal in cross section.
Axial parenchyma apotracheal and paratracheal; fusiform and strands of 2−10 cells or more; storied structure. Apo- tracheal parenchyma uni- or biseriate tangential bands in latewood. Paratracheal parenchyma vasicentric around wide vessels and narrow vessels. Crystals absent.
Rays heterocellular. Multiseriate rays 120−900 (mean 558) µm tall and 25−115 (mean 67) µm wide; composed of tile cells and procumbent cells. Tile cells 11.4−19 (mean 14.8)
×19−26.6 (mean 18.2)×7.6−11.4 (mean 10.2) µm in tangential
×vertical×radial diameters. Procumbent cells 7.6−11.4 (mean 9.8)×9.5−15.2 (mean 12.5)×24.7−62.7 (mean 46) µm in tangen- tial×vertical×radial diameters. Rarely crystals present.
4. DISCUSSION
Among the 64 silicified fossil woods from the Tertiary Upper Coal-bearing Formation, four specimens were char- acterized by 1) their distinct ring porosity with wide vessels in earlywood, 2) their solitary narrow vessels in latewood, 3) the presence of tile cells in heterogeneous rays, 4) the absence of helical thickening and 5) their exclusively sim- ple perforation plate. The tile cells are empty upright ray cells that found among horizontal procumbent ray cells.
They have been found in the woods belonging to four fam- ilies of the Malvales--Sterculiaceae, Tiliaceae, Bombacaceae, Malvaceae (Chattaway, 1933). The tile cells are classified into three type; Durio, Pterospermum and intermediate type (IAWA committee, 1989). The tile cells of our fossil woods are small to large ellipses in tangential view and very thin to a little wide in radial view. Therefore, those tile cells belong to the Pterospermum type and/or the intermediate type.
Up until now, the presence of the tile cells were reported in 14 species of fossil woods (Wheeler, 1991; Terada and Suzuki, 1998). Among them, only three species of Wataria and a species of Reevesia have the ring porosity (Terada
Miocene of Honshu, Japan. The three species are identified by their sizes and layers of wide vessels in earlywood (Terada and Suzuki, 1998). One of the four fossils (KNU 0010) was characterized by one to three layers and 195−325 (mean 252) µm of the tangential diameter of wide vessels and identified as W. miocenica. The remaining three (KNU 0008, 0019, 0044) have one to three layers and 125−250 (mean 181) µm of the tangential diameter of wide vessels and were identified as W. parvipora.
The East Sea (or Sea of Japan) is believed to be formed during Oligocene or Early Miocene (Lallemand and Jolivet, 1985). This means that Korean Peninsula and some of Jap- anese islands were built on the same terrestrial continent.
Therefore, they constituted the same flora in both areas.
According to the monographic study of fossil woods from Tertiary formations in Japan (Terada, 1998), fossil woods of Wataria were produced from five Miocene Formations-- Atsumi, Nawamata, Zenpouji, Nakamura, Hachiya Formations.
W. miocenica was produced from the Atsumi, Nawamata, Zenpouji Formations and W. parvipora from the Nakamura, Hachiya Formations. It is noticeable that none of Japanese Formations produced both of species. However, both spe- cies--W. miocenica and W. parvipora--were produced in the Upper Coal-bearing Formation, which is a relatively narrow area. Therefore, it can be said that the Tertiary flora of the Upper Coal-bearing Formation might be more variable than others.
As well, there are no relatives distributed in Japan and Korean Peninsula. Therefore, the Wataria is an extinct com- mon constituent of Tertiary flora in both of Japan and Korea. The creation of the same species in Korea and Japan could suggest that the floras of those two areas were fun- damentally identical during the Tertiary age.
As mentioned above, there are some inconsistencies in presuming which age Janggi fossils belong to. Based on the flora of fossil leaves, Huzioka (1972) supposed that they belong to the Early Miocene. Meanwhile, Tateiwa (1924) and Chun (1982) supposed that they come from the Oli- gocene. In Japan, all formations which produced W. mio- cenica and W. parvipora belong to the Early to Middle Miocene. After comparing between the Upper Coal-bearing Formation’s and Japan’s formations, we concluded that the Upper Coal-bearing Formation fossils might be formed dur- ing the Early to Middle Miocene.
Wataria belongs to the Sterculiaceae and most of Stercu- liaceae are found in the tropics. Triplochiton, which is con-
sidered as a plant closely related with Wataria (Terada and Suzuki, 1998), is also a tropical plant. The only plant in the Sterculiaceae with the typical ring porosity is Firmiana, which is found in warm temperate East Asia. In this regard, it can be said that the climate of the period when the Upper Coal-bearing Formation was made might be warmer than that of the present age.
ACKNOWLEDGMENTS: This paper was supported (in part) by research funds of Chonbuk National University.
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Manuscript received January 29, 2003 Manuscript accepted April 30, 2003
