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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Brief Report on a New Material of Ashicaulis (Osmundaceae, Filicales) from the Middle Jurassic of Western Liaoning, NE China 234 Ning Tian 1,2 , Yongdong Wang 1 , Wu Zhang 3 , Zikun Jiang 1 1 Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China 2 Key Lab of Western China's Environmental Systems of the Ministry of Education, Lanzhou University, Lanzhou 730000, China 3 Shenyang Institute of Geology and Mineral Resources, Ministry of Land and Resources (E-mail: tianning84@163.com) The Osmundaceae is a primitive family of Fili- cales which receives much concern of palaeobotanists because of its peculiar characters of sporangia, phylo- genetic relationships and extensive fossil records. The Osmundaceae contains only 21 extant species distri- buted among the genera Osmunda, Todea and Lepto- pteris (Hewitson, 1962). The osmundaceous ferns were diverse and widespread in the geological time, more than 180 fossil species have been described so far repre- sented by compressed foliage, isolated spores and sporangia and permineralized stems (Tidwell and Ash, 1994); among them, over 80 species are based on permineralized rhizomes or stems. The earliest fossil evidence of the Osmundaceae can be traced back to the Early Permian (Rößler and Galtier, 2002). Molecular and morphological data of living species suggest that the origin of this family is the Late Carboniferous (Pryer et al., 2004). This group has been regarded by many authors as intermediate between the eus- porangiate and leptosporangiate ferns, while the latest molecular studies place the Osmundaceae as sister group to the rest of the leptosporangiate ferns (Pryer et al., 2004). During the past decades, some well preserved petrified osmundaceous rhizomes have been described from the Middle Jurassic of western Liaoning and northern Hebei Provinces, NE China. It is considered this region to be one of the most significant petrified osmundaceous fossil localities in Northern Hemisphere. To date, 3 species of Ashicaulis and 2 species of Millerocaulis have been described from northeastern China (Wang, 1983; Zhang and Zheng, 1991; Matsu- moto et al., 2006; Cheng and Li, 2007; Cheng et al., 2007). The present paper is to briefly report a new species referred to Ashicaulis by comparison with living and fossil fern rhizomes in the subfamily Osmun- doideae. The specimen is collected from the Middle Jura- ssic Tiaojishan (Lanqi) Formation in Beipiao County, western Liaoning Province. It is about 4-4.5 mm in diameter, and is composed of pith, xylem cylinder, a two-layered cortex, adventitious roots and numerous petiole bases. In cross section, the stem shows an ectophloic-dictyoxylic siphonostele consisting of 24- 32 xylem strands; Xylem cylinder consists of 11-13 xylem strands, and is about 0.8-1.2 mm (12 to 15 tracheids) in thickness. Most of xylem segments are separated by complete leaf gaps and rare incomplete leaf gaps; Leaf gaps are mostly delayed type. The pith is with an ill preservation, 1.5-3.5 mm in diameter. Inner cortex is poorly preserved, and the outer cortex is sclerenchymatous; the whole cortex consists of about 22-25 leaf traces. Leaf traces are mostly adaxially concave with endarch single protoxylem cluster which bifurcates when entering into the outer cortex. Petiole bases are spirally arranged surrounding the stele, and each one bears two lateral wings. The petiole bases consist of a parenchymatous outer cortex, a homogeneous sclerotic ring, a C-shaped vascular bundle, a sclerenchyma mass at the concavity of the vascular bundle. The shapes and composition of the petiole base change in different position; Immediately proximal to the junction of the stele, the petiole base bears relatively short stipular wings (5 mm wide and 3.5 mm high), and the sclerenchyma mass in the stipular wings and concavity of the vascular bundle are absent. Distally, the stipular wings become longer (8.0 mm wide and 2.5 mm high), and the sclerenchyma mass is present in the vascular bundle concavity, and nearly oval in shape. In the most distal levels, the length of the lateral wings are much more longer (10.0 mm wide and 3.5 mm high), and sclerenchyma masses in the stipular wings and concavity of the vascular bundle can all be observed, sclerenchyma masses in the vascular bundle concavity ranged from oval to kidney in shape. In addition, at such levels of the petiole bases, some thick- walled fibers also exist in stipular wings irregularly. Of interest, adventitious root traces are well developed in the new species. Typically, they mostly diverge from the leaf trace or petiole bases, merely minority of them are directly from vascular strands of the stele. Xylem of these root are diarch. Depend on the diagnostic combination of characters (ectophloic dictyoxylic siphonostele, complete leaf gaps, oval sclerotic ring), the present specimen exhibit more similarity with the genus of Ashicaulis. Since it differs from the Osmundacaulis, Millerocaulis and Aurealcaulis in stele type; additionally, it is also distinct from the Palaeosmunda in bearing oval sclerotic ring. In the classification of the different species of the osmundaceous genera, the arrangement of sclerenchyma in the stem and petiole bases is considered a key feature (Hewitson, 1962; Miller, 1967, 1971; Cheng and Li, 2007; Tian et al., 2008). Some other features,
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 such as the stem diameter, stele diameter, pith diameter, xylem cylinder, cortex thickness and trace number are also important distinguishing characters at species level. This species is characterized by the presence of an crescent-shaped sclerenchyma mass in the concavity of petiolar vascular strands, one large mass and several small sclerenchymatous in each stipular wing, and homogeneous sclerenchyma ring in the petiole bases. When comparing with other known species of the Ashicaulis in these identification features, our specimen is considered to be distinct from all the previously reported Ashicaulis species, hence the authors prefer to regard it as a new taxon referred to Ashicaulis. As the sixth described osmundaceous rhizome from the Middle Jurassic of northeastern China, the new material helps to further understand the radiation of the family Osmundaceae in the Northern Hemi- sphere. The new species seems to show many similarities in anatomical characters with the A. liaoning- ensis from the same locality and A. woolfei from North America. Furthermore, anatomical similarities in the distribution of sclerenchyma tissues of the petiole base between the new taxon and the modern species Osmunda pluma indicates that the new species be a possible precursor of the subgenus Osmunda. Our new species may provide valuable informa- tion for understanding the developing trace and geological occurrences of the osmundaceous rhizomes in the northern hemisphere. It is noted when compared with the species referred to the extant genus Osmunda, the new material shares a great similarity with the O. shimokawaensis from the Middle Miocene of Hokkaido, Japan. Though the O. shimokawaensis is with a distinct bigger size in shape (20 cm long and 4-7 cm in diameter), the stele characters (thickness and xylem strand number of the xylem cylinder, homogeneous sclerotic ring, as well as leaf trace number in the inner and outer cortex) really approach our new specimen. Particularly, sclerenchyma tissue distribution pattern in petiole base of the new taxa is extremely comparable with the earlier stages of that in O. shimokawaensis (Matsumoto and Nishida, 2003). Of interest, this may indicate the two species are closely related with each other, and the O. shimokawaensis may be derived form the present species. Additionally, it also provides a clue for inter- preting the Miocene osmundaceous rhizome species of Japan may not immigrated from North American, but from northeast China. The new hypothesis is more easily understandable in the the view of palaeo- geography. O. shimokawaensis is assigned to the subgenus Osmunda; hence the authors may propose that the new material from China be a close relative of the living species of subgenus Osmunda and O. shimokawaensis be an important intermediate in the evolution from Ashicaulis to subgenus Osmunda. Acknowledgements: Sincere appreciations are due to Prof. Zheng, S.L. (Shenyang Institute of Geo- logy and Mineral Resources, Shenyang) for his kind suggestions. This work was partly supported by National Key Basic Research Program of China (2006CB701401), National Natural Science Foun- dation of China (No. 40972008) and the Pilot Project of the Knowledge Innovation Program, CAS (KZCX2- YW-154). This is a contribution to IGCP 506. The first author is also supported by the Visiting Scholar Project of Lanzhou University for Domestic Doctoral Student (2008). Key words: Ashicaulis; Osmundaceae; Tiao- jishan Formation; Middle Jurassic; Liaoning Province References: Cheng Y.M., Li C.S. A new species of Millerocaulis (Osmundaceae, Filicales) from the Middle Jurassic of China. Review of Palaeobotany and Palynology, 2007, 144: 249-259. Cheng Y.M., Wang Y.F., Li C.S. A new species of Millerocaulis (Osmundaceae) from the Middle Jurassic of China and its implication for evolution of Osmunda. International Journal of Plant Science, 2007, 168: 1351-1358. Hewitson W. Comparative morphology of the Osmun- daceae. Annals of the Missouri Botanical Garden, 1962, 49: 57-93. Matsumoto M., Nishida H. Osmunda shimokawaensis sp. nov. and Osmunda cinnamomea L. based on permineralized rhizomes from the Middle Miocene of Shimokawa, Hokkaido, Japan. Paleon- tological Research, 2003, 7: 153-165. Miller C.N. Evolution of the fern genus Osmunda. Contribution from the Museum of Palaeontology, The University of Michigan, 1967, 21: 139-203. Miller C.N. Evolution of fern family Osmundaceae based on anatomical studies. Contribution from the Museum of Palaeontology, The University of Michigan, 1971, 23: 105-169. Pryer K.M., Schuettpelz E., Wolf P.G., et al. Phylogeny and Evolution of ferns (Monilophytes) with a focus on the early leptosporangiate divergences. American Journal of Botany, 2004, 91: 1582- 1598. Rößler R., Galtier J. First Grammatopteris tree ferns from the Southern Hemisphere e new insights in the evolution of the Osmundaceae from the Per- mian of Brazil. Review of Palaeobotany and Palynology, 2002, 121: 205-230. Tian N., Wang Y.D., Jiang Z.K. Permineralized rhizomes of the Osmundaceae (Filicales): Diversity and tempo-spatial distribution pattern. Palaeo- world, 2008, 17: 183-200. Tidwell W.D. Ashicaulis, a new genus for some species of Millerocaulis (Osmundaceae). Sida Contri- bution of Botany, 1994, 16: 253-261. Tidwell W.D., Ash S.R. A review of selected Triassic to Early Cretaceous ferns. Journal of Plant Research, 1994, 107: 417-442. Wang Z.Q. Osmundacaulis hebeiensis, A new species 235
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