CZEKANOWSKIA FROM THE JURASSIC OF INNER MONGOLIA, CHINA

Chunlin Sun,1,*,y David L. Dilcher,*,y Hongshan Wang,y Ge Sun,* and Yuhui Ge*

*Key Lab for Evolution of Past Life and Environment in Northeast Asia, Ministry of Education, 6 Ximinzhu Street, Changchun 130026,Jilin, China; and yFlorida Museum of Natural History, University of Florida, Gainesville, Florida 32611-7800, U.S.A.

The genus Czekanowskia is an important member of the Mesozoic flora and is widespread in the NorthernHemisphere. In China, it is found mostly in Late Triassic and Early and Middle Jurassic sediments of NorthChina. With the exception of a few specimens, all the reports of this genus from China have been basedon gross leaf morphology. Abundant Czekanowskia leaves, preserved as compression fossils, were collectedfrom the Middle Jurassic, Zhaogou Formation of Inner Mongolia, China. In this article, two subgenera ofCzekanowskia, Harrisella and Vachrameevia, are recognized from Inner Mongolia, China, on the basis of leafmorphology and epidermal characters. Two new species, Czekanowskia chinensis sp. nov. (subg. Harrisella)and Czekanowskia shiguaiensis sp. nov. (subg. Vachrameevia), are described. The occurrence of these speciesin the Middle Jurassic of Inner Mongolia significantly extends the stratigraphic and geographic distribution ofCzekanowskia in the Northern Hemisphere. Analysis of the epidermal characters of material presented herealong with consideration of other associated plants of the flora and sedimentology of the plant-bearing stratasuggests that the two species described in this report grew in an area with a warm and humid climate in a warmtemperate zone. Biostratigraphic correlation of the plant-bearing strata indicates that the specimens describedhere are Middle Jurassic in age.

Keywords: Czekanowskia, Middle Jurassic, Inner Mongolia, China.

Introduction

Czekanowskia, an important member of Late Triassic andEarly and Middle Jurassic floras, is common and widely dis-tributed in the Northern Hemisphere. It has been reportedfrom Eastern Greenland (Harris 1926, 1935), England (Harrisand Miller 1974), Sweden (Nathorst 1906; Johansson 1922),Romania (Popa and van Konijnenburg-van Cittert 2006),Kazakhstan, Eastern Ural, Central Asia, Siberia (Doludenkoand Rasskazova 1972; Samylina and Kiritchkova 1991, 1993;Kostina 1999, 2004), China (Sze et al. 1963; Ye et al. 1986; Liet al. 1988; Mi et al. 1993, 1996; Sun 1993; Li 1995), Japan(Kimura and Ohana 1979), the United States, and Canada(Ash and Basinger 1991; Ash 1994).

Czekanowskia was first described by Heer (1876) on thebasis of material from the Irkutsk Jurassic coal-bearing basinof Eastern Siberia. Since then, many fossil leaves have beendiscovered throughout the Northern Hemisphere. Most ofthem were assigned to Czekanowskia setacea Heer and Cze-kanowskia rigida Heer on the basis of leaf morphology. Thecuticle of C. setacea Heer from the type locality in Siberiaand C. rigida Heer also from Siberia, but not the type locality,was studied by Florin (1936) and Vachrameev and Doludenko(1961). Cuticle of C. rigida Heer found in other areas was alsodescribed from the basal Liassic of Sweden (Nathorst 1906;Johansson 1922) and the Lower Cretaceous of Franz-Joseph-Land (Florin 1936).

Cuticular material belonging to other species of Czeka-nowskia was studied from other areas of the world, for ex-

ample, from Yorkshire by Seward (1900, 1919), Black(1929), and Harris and Miller (1974); from Eastern Green-land by Harris (1926, 1935); from Japan by Oishi (1932)and Kimura and Ohana (1979); and from the United Statesby Ash (1994).

Samylina and Kiritchkova (1991, 1993) studied well-preserved cuticle of the genus Czekanowskia collected frommore than 170 localities in the former Soviet Union. They di-vided the genus into three subgenera on the basis of leafepidermal characters, that is, Czekanowskia (leaves amphis-tomatic with stomata arranged in files), Harrisella (leavesamphistomatic with stomata arranged in bands, at least onthe lower epidermis), and Vachrameevia (leaves hypostomaticwith stomata arranged in files or bands).

So far, ;80 species of the genus Czekanowskia have beenestablished on the basis of differences of cuticular features.Sixty-five species were assigned to the subgenus Czekanow-skia, including two species from Eastern Greenland (Harris1926, 1935), four species from Yorkshire (Harris and Miller1974), one species from the United States (Ash 1994), onespecies from Sweden (Johansson 1922), one species from Ja-pan (Kimura and Ohana 1979), and 56 species from the for-mer Soviet Union (Samylina and Kiritchkova 1991, 1993).Eight species were assigned to the subgenus Harrisella andseven species to the subgenus Vachrameevia from the formerSoviet Union (Samylina and Kiritchkova 1991). Fossils of thesubgenus Vachrameevia were reported from the Jurassic ofNorthwest China (Wu et al. 2002).

Czekanowskia was thought to belong to the order Gink-goales (Florin 1936). Pant (1957) established the order Cze-kanowskiales, but he did not provide a diagnosis. After fruitsof Leptostrobus were studied (Harris 1935, 1951; Krassilov

1 Author for correspondence; e-mail: clsun@mail.jlu.edu.cn.

Manuscript received April 2009; revised manuscript received June 2009.

1183

Int. J. Plant Sci. 170(9):1183–1194. 2009.

� 2009 by The University of Chicago. All rights reserved.

1058-5893/2009/17009-0006$15.00 DOI: 10.1086/605869

1970; Harris and Miller 1974), these authors adopted andused the order name Czekanowskiales. Since then, Czeka-nowskiales has been adopted by most paleobotanists. Nowthe order Czekanowskiales includes the genera Czekanow-skia Heer, Solenites Lindley and Hutton, Hartzia Harris,Sphenarion Harris, Phoenicopsis Heer, Arctobaiera Florin,the ovulate reproductive organ Leptostrobus Heer, and theprobable staminate organ Ixostrobus Raciborski.

Material and Methods: Geological Setting

The specimens examined were collected from the ShiguaiBasin, a well-known Jurassic coal-bearing basin in northChina. This Jurassic nonmarine coal-bearing basin is located

in the southwestern part of Inner Mongolia (fig. 1). In thisbasin, the Jurassic sediments are well developed and are espe-cially well exposed at the Toudaogou-Erdaogou Section. TheJurassic strata are divided into four formations in ascendingorder (Geological and Mineral Resources Bureau of InnerMongolia Autonomous Region 1991): the Lower JurassicWudanggou Formation, the Middle Jurassic Zhaogou andChanghangou Formations, and the Upper Jurassic Daqing-shan Formation (fig. 2). From 1999 to 2002, many fossilplants were collected from the Lower and Middle membersof the Zhaogou Formation at the Toudaogou-Erdaogou sec-tion by the authors and their colleagues. Our preliminaryexamination shows that this is a large and diverse flora consist-ing of ferns, cycads, ginkgos, and conifers; it is dominated byginkgos, czekanowskias, and conifers.

Fig. 1 Map of the Shiguai Basin in Inner Mongolia, China. A, Map showing the location of Inner Mongolia in China. B, Map showing the

location of the Shiguai Basin in southwestern Inner Mongolia. C, Generalized regional outcrop map of the Lower Jurassic Wudanggou Formation,

the Middle Jurassic Zhaogou Formation, and the Changhangou Formation in the Shiguai basin. The leaf fossils examined in this article were

collected from the Zhaogou Formation.

1184 INTERNATIONAL JOURNAL OF PLANT SCIENCES

Lithologically, the Zhaogou Formation can be subdividedinto three members on the basis of our field investigation.The lower member is represented by fluvial and swamp sedi-ments consisting of conglomerates, sandstones, siltstones,shales, and coal layers. Abundant fossil leaves were mainlycollected from the fine-grade sandstone bed in the lower partof this member. Also some bivalves were found in this mem-ber. The middle member consists of sandstones, siltstones,shales, and coal beds, indicating deposition in a lacustrine orswamp environment. This member consists mainly of coal-bearing deposits. The upper member is typically lacustrinesediments consisting of conglomerates, sandstones, siltstones,oil shale, calcic shale, and freshwater limestone, which yieldfossil fish, conchostracans, and insects.

More than 20 compression specimens were collected fromthe lower part of the Middle Jurassic Zhaogou Formation.Six specimens with well-preserved cuticles were examined atthe Research Center of Paleontology and Stratigraphy of JilinUniversity, Changchun, China, and cuticular preparationswere made from them using standard procedures (see Dilcher1974). During this procedure, the cuticle was mechanicallyremoved from the specimens using HF, Schulze’s solution,and 5% NH4OH. Samples were then air dried before mount-

ing on SEM stubs and then coated with platinum. After that,the preparations were examined using a JSM-6700 SEM at anacceleration voltage of 10 kV. All specimens and preparationsare stored in the Research Center of Paleontology and Stratig-raphy of Jilin University, Changchun, China.

Systematics

Order—Czekanowskiales Pant 1957

Genus—Czekanowskia (Heer) Harris and Miller 1974

Remarks. According to Harris and Miller (1974) and Sa-mylina and Kiritchkova (1991, 1993), the filiform leaves arewedge shaped as a whole and are borne in bundles on cadu-cous short shoots covered with persistent scale leaves. Theleaves branch dichotomously one to three times. The result-ing leaf segments are usually 90–150 mm long and 0.5–2.5mm wide. The leaf lamina is thick, oval, trapezoidal-like orrectangular in cross section. Usually there is a single incon-spicuous vein in each filiform leaf lamina. Resin bodies areabsent.

The leaves are amphistomatic or hypostomatic. The sto-mata are longitudinally oriented and arranged in files orbands. The guard cells are sunken in a pore formed normallyby four to six subsidiary cells, two of which are usually ter-minal. The pore is commonly surrounded by a rim or papil-lae of subsidiary cells. Ordinary epidermal cell walls areusually arranged in longitudinal files and have straight or sin-uous side walls.

On the basis of the distribution and arrangement of the sto-mata on the epidermis, Samylina and Kiritchkova (1991) di-vided Czekanowskia into three subgenera: Czekanowskia,Harrisella, and Vachrameevia. The leaves of the subgenusCzekanowskia are amphistomatic, with stomata arranged insingle files on both sides. Although the leaves of the subgenusHarrisella are also amphistomatic, the stomata are arrangedin broad bands (at least on the lower epidermis). The leaves ofthe subgenus Vachrameevia are hypostomatic, with stomataarranged in files or broad bands only on the lower epidermis.

In this report, we follow Samylina and Kiritchkova’s (1991)proposal and assign the specimens from Inner Mongolia ofChina to the two subgenera Czekanowskia (subg. Harrisella)and Czekanowskia (subg. Vachrameevia) on the basis of theircuticular features.

Subgenus—Czekanowskia (subg. Harrisella)Kiritchkova and Samylina 1991

Species—Czekanowskia (subg. Harrisella) chinensissp. nov. Sun, Dilcher, Wang, Sun et Ge (Figs. 3–6)

Holotype. Specimen S012 (fig. 3A).Paratype. S004 (fig. 3B).Repository. The Research Center of Paleontology and

Stratigraphy of Jilin University, China.Type locality. Toudaogou-Erdaogou Section, Shiguai Coal

Mine, Inner Mongolia, China.Stratum typicum. Fine-grained sandstone of the Lower Mem-

ber of Zhaogou Formation.Etymology. The specific epithet chinensis refers to the

first report of this species from China.

Fig. 2 Diagram showing the division of the Lower and Middle

Jurassic strata in the Shiguai Basin, Inner Mongolia, China. The plantfossils described in this article were collected from the Lower Member

of the Zhaogou Formation.

1185SUN ET AL.—JURASSIC CZEKANOWSKIA OF INNER MONGOLIA, CHINA

Diagnosis. Six linear leaves attached in a bundle on theshort shoot. Leaves dichotomizing two or three times at 10�–25� angles with leaf segments 0.6–1 mm wide. Leaves am-phistomatic. Stomata longitudinally arranged in broad bandson the upper and lower epidermis. Two bands (each bandcontaining two files of stomata) present on the upper epider-mis and two bands (each band containing three to four files ofstomata) present on the lower epidermis. Stomata surroundedby four to six subsidiary cells with unevenly developed papil-lae. Trichomes and papillae absent on the periclinal cell walls.

Description. The leaves are in bundles of six, and theirlength is more than 100 mm. They dichotomize two or threetimes. Each leaf is ;0.8–1 mm wide at the base and increasesup to 2 mm wide before branching. The final segments are0.6–1 mm wide. The single vein is inconspicuous (fig. 3A, 3B).

The cuticle was removed from the middle and distal por-tions of the leaf (fig. 3A, 3B). The leaves are amphistomaticwith longitudinally oriented stomata. There are two stomatalbands (each contains two files of stomata) and one nonsto-matal zone on the upper cuticle. In the nonstomatal zone(;350 mm wide), epidermal cells are 20–100 mm long 3 10–15 mm wide and are arranged in longitudinal files. The sto-matal zones are 250 mm wide (fig. 4A). Within the stomatalzones, the ordinary epidermal cells between the stomatal files

are commonly irregularly rectangle with truncate or pointedends (10–50 mm long and 12–14 mm wide), and those cellsbetween the stomatal complexes are irregularly square (eachside ;10–14 mm long).

The stomatal complexes are 58–67 mm long 3 35–42 mmwide. Guard cells are commonly surrounded by five to sixrandomly oriented subsidiary cells, with one at each polarend of the guard cells and one or two lateral to the guardcells (fig. 4B). The guard cells are slightly sunken below thesurface of subsidiary cells. Cuticular thickenings are presenton the anticlinal walls adjacent to the stoma. The inner ringof subsidiary cells is unevenly papillate (papillae of differentsizes). The papillae partially cover the stomatal pit (fig. 4C).

Two stomatal bands, each containing three to four stoma-tal files, and one nonstomatal zone are present on the lowerepidermis (fig. 4D). The stomatal zones are 400–450 mmwide, and the ordinary epidermal cells are irregularly rectan-gular (30–50 mm long and 12–18 mm wide) or irregularlysquare (each side ;12–20 mm long). Nonstomatal zones are300–350 mm wide. The epidermal cells in these zones mayhave truncated or pointed ends and are very elongated rect-angular (60–120 mm long and 10–12 mm wide).

The stomatal complexes are 72–78 mm long and 50–65mm wide. Stomata are commonly surrounded by four to six

Fig. 3 Leaves of Czekanowskia (subg. Harrisella) chinensis sp. nov. A, S012, specimen showing two bundles of linear leaves (arrow indicates

the position where cuticle was removed for preparation). Scale bar ¼ 1 cm. B, S004, specimen showing a bundle of linear leaves superimposed by aGinkgo leaf at the bottom (arrow indicates the position where cuticle was removed for preparation). Scale bar ¼ 1 cm.

1186 INTERNATIONAL JOURNAL OF PLANT SCIENCES

subsidiary cells, with one at each polar end of the stomataand one or two on each lateral side (fig. 4E, 4F). The guardcells are sunken in the stomatal pit or pore, and cuticularthickenings occur on the anticlinal walls adjacent to thestoma. The inner ring of subsidiary cells is unevenly papil-late. The papillae may partially cover the stomatal pit (fig.5A) or most of it (fig. 5B). The outer ring exhibits unevenlydeveloped cuticular thickenings (fig. 5C, 5D).

The anticlinal cell walls of ordinary epidermal cells onboth the upper and lower epidermis are straight and thick-ened by striations. The periclinal cell walls are unevenlythickened (fig. 6A, 6B). Trichomes and papillae are absent onthe periclinal cell walls.

Comparison

Only eight species of Czekanowskia (subg. Harrisella)have been reported from Jurassic deposits of the former So-viet Union (Samylina and Kiritchkova 1991). This is the firstreport of this subgenus from China.

The new species is comparable with Czekanowskia (subg.Harrisella) amphistomatica Kiritchkova and Samylina (Samy-lina and Kiritchkova 1991, p. 80, pl. II, fig. 2; pl. LIV, figs.1–4; text fig. 44) from the Middle Jurassic of central Asia,Czekanowskia (subg. Harrisella) ketovae Orlovskaya (Dolu-denko and Orlovskaya 1976, p. 75, pl. XXXII, figs. 5–7; pl.XXXIII, figs. 1–4; pl. XXXIV, figs. 1–6; text figs. a–c; Samy-lina and Kiritchkova 1991, p. 83, pl. LVI, figs. 1–4; text fig.46) from the Early-Middle Jurassic of southern Kazakhstan,and Czekanowskia (subg. Harrisella) robusta Kiritchkovaand Samylina (Samylina and Kiritchkova 1991, p. 87, pl. V,fig. 4; pl. LIX, figs. 1–5; text fig. 49) from the Late Jurassicof Middle Asia.

The leaf segments of C. (subg. Harrisella) amphistomaticaKiritchkova and Samylina are usually 2.5–3 mm wide, andeach segment has four to five stomatal bands on the lowerepidermis. The width of the stomatal bands near the marginof the leaf segment is narrower than that in the center part ofthe segment. The leaf segments of C. (subg. Harrisella) keto-vae Orlovskaya are 2–3 mm wide, and each segment hasfour to five stomatal bands on the lower epidermis. The sto-matal complexes are 27–44 mm long and 21–34 mm wide.The new species is similar to C. (Harrisella) robusta Kiritch-kova and Samylina in gross morphology. However, the widthof the leaf segments of C. (Harrisella) robusta is ;1–1.5 mmwide, and it increases up to 2–2.5 mm wide before branchingat the middle part of the leaves. Three to four stomatal bandswith each containing two to three stomatal files are presenton the lower epidermis. Papillae are also present on the peri-clinal walls of lower and upper epidermis.

Both trichomes and papillae are absent on the periclinalcell walls of the new species, while they are present and dis-tinctive on the periclinal walls of the lower epidermis of allother five known species. In addition, the size of the leaves,the number of stomatal bands in each leaf segment, and thenumber of stomatal files in each bank are also different. Theleaf segments of Czekanowskia (subg. Harrisella) buninaeKiritchkova and Samylina (Samylina and Kiritchkova 1991,p. 81, pl. II, fig. 5; pl. V, fig. 8; pl. LV, figs. 1–5; text fig. 45)from the Middle Jurassic of northern Kazakhstan are ;2–3

mm wide. Each segment has five to seven stomatal bands onthe lower epidermis. The leaf segments of Czekanowskia(subg. Harrisella) mchatica Kiritchkova and Samylina (Samy-lina and Kiritchkova 1991, p. 84, pl. LVII, figs. 1–4; text fig.47) from the Middle Jurassic of northern Kazakhstan are1.75–2 mm wide. There are three stomatal bands, each con-taining two to four stomatal files on the lower epidermis.The leaf segments of Czekanowskia (subg. Harrisella) orlov-skajae Kiritchkova and Samylina (Samylina and Kiritchkova1991, p. 85, pl. I, fig. 17; pl. III, fig. 5; pl. LVIII, figs. 1–4;text fig. 48) from the Early Jurassic of eastern Kazakhstanare 2–2.5 mm wide and exhibit four to five stomatal bandson the lower epidermis; each band consists of four to fivestomatal files. The leaf segments of Czekanowskia (subg.Harrisella) striata Kiritchkova and Samylina (Samylina andKiritchkova 1991, p. 89, pl. V, fig. 5; pl. LX, figs. 1–6; text fig.50) from the Middle Jurassic of northern Kazakhstan are 2–3mm wide. Each segment has four to seven stomatal bandson the lower epidermis, and each band consists of four to sixstomatal files.

The leaf segments of Czekanowskia (subg. Harrisella) veraKiritchkova and Samylina (Samylina and Kiritchkova 1991,p. 91, pl. LXIII, figs. 1–3; text fig. 51) from the Late Jurassicof western Siberia are 1–1.5 mm wide. Each segment hasthree to four stomatal bands on the lower epidermis, andeach band consists of three to four stomatal files. Trichomesand papillae are also present on the periclinal walls. The pa-pillae on the subsidiary cells cover the stomatal pit.

Subgenus—Czekanowskia (subg. Vachrameevia) (Heer)Kiritchkova and Samylina 1991

Species—Czekanowskia (subg. Vachrameevia) shiguaiensissp. nov. Sun, Dilcher, Wang, Sun et Ge (Figs. 7, 8)

Holotype. S005 (fig. 7A).Repository. The Research Center of Paleontology and

Stratigraphy of Jilin University, China.Type locality. Toudaogou-Erdaogou Section, Shiguai Coal

Mine, Inner Mongolia, China.Stratum typicum. Fine-grained sandstone of the Lower

Member of Zhaogou Formation, Middle Jurassic.Etymology. The specific epithet shiguaiensis refers to the

Shiguai coal mine, Inner Mongolia, China, where the holo-type specimen was collected.

Diagnosis. Linear leaves attached in a bundle more than130 mm long; leaves dichotomously branching more thanthree times at 5�–15� angles. Leaf segments 0.7–1.1 mm inwidth. Leaves hypostomatic. Ordinary epidermal cells ar-ranged in files on the upper epidermis, mainly rectangular tosquare. Two stomatal bands present on the lower epidermis,with each band consisting of two to three stomatal files. Theordinary epidermal cells are irregularly square in shape. Onthe nonstomatal zone, the epidermal cells elongated rectan-gular in shape. Stomata surrounded by four to six subsidiarycells. Stomatal complex rounded or elliptic. Papillae and tri-chomes are absent on both upper and lower epidermis.

Description. Four linear leaves in a bundle and are morethan 130 mm long. Each leaf dichotomizes at least threetimes (fig. 7A). The leaf segments are ;0.7–1 mm wide andbecome somewhat wider below the first branching (up to 1.2

1187SUN ET AL.—JURASSIC CZEKANOWSKIA OF INNER MONGOLIA, CHINA

mm wide). An inconspicuous single vein is present in eachsegment of the leaves.

The leaves are hypostomatic. The cuticle is thin on bothupper and lower epidermis. On the upper epidermis, the cellsare arranged in longitudinal files (fig. 7B, 7C; fig. 8A). Theyare mostly rectangular or square and are 15–30 mm long and12–18 mm wide.

Two stomata bands (each containing two to three stomatalfiles) and one nonstomatal zone are present on the lower epi-dermis (fig. 7B). In the stomatal zones, ordinary epidermalcells are commonly irregularly square, with each side ;12–14 mm long. Ordinary cells on the nonstomatal zone areelongated rectangular (20–50 mm long and 12–16 mm wide)and are arranged in files (fig. 7B, 7C).

The stomatal complexes are rounded or elliptic in shapeand are 60–63 mm long and 45–60 mm wide. The stomataare longitudinally oriented. The guard cells are surroundedby four to six subsidiary cells (fig. 8B, 8C). Often there isone cell at each polar region and one or two on two lateralsides. The guard cells are slightly sunken below the surfaceof subsidiary cells, resulting in an epistomatal chamber en-closed by the subsidiary cells. Cuticular thickenings (irregularpapillae) are present on the guard cell anticlinal walls adja-cent to the stomata.

On both the upper and the lower epidermis, the anticlinalwalls of cells outside of the stomatal bands are straight andthickened by striations (fig. 8D). Their periclinal walls areunevenly thickened. Both papillae and trichomes are absent.

Discussion and Comparison

The new species differs from Czekanowskia (subg. Czeka-nowskia) and Czekanowskia (subg. Harrisella) in having hy-postomatic leaves and the presence of stomatal bands on thelower epidermis. Seven species of the subgenus Vachrameeviahave been described from the Jurassic deposits of China (Wuet al. 2002) and the former Soviet Union (Samylina and Kir-itchkova 1991) on the basis of leaf epidermal features.

Among the known species from Russia, the new species issomewhat similar to Czekanowskia (subg. Vachrameevia)baikalica Kirichkova and Samylina from the Lower or Mid-dle Jurassic of Siberia (Samylina and Kiritchkova 1991, p.91, pl. LXIII, text fig. 51) in lacking papillae and trichomeson the periclinal walls of nonstomatal band cells, having twostomatal bands (each band containing two to three stomatalfiles) on the lower epidermis. They differ significantly in theform of regular epidermal cells on both the lower and the up-per epidermis. The ordinary epidermal cells of the upper epi-dermis of C. (subg. Vachrameevia) baikalica are mainlyelongated rectangular in shape, and the cells in the stomatal

zones of the lower epidermis are rectangular in shape. Theshape and size (15–38 mm and 33–55 mm) of stomatal com-plexes, the number of leaves in a bundle (six leaves), and thewidth of the leaf segments (1.5–2 mm) of C. (subg. Vachra-meevia) baikalica are also different from the new species.

The other six known species obviously differ from the newspecies in gross morphology and in epidermal features. Theleaf segments of Czekanowskia (subg. Vachrameevia) aus-tralis Kiritchkova and Samylina from the Early-Middle Juras-sic of southern Kazakhstan (Samylina and Kiritchkova 1991,p. 91, pl. II, fig. 19; pl. VI, fig. 8; pl. XV, figs. 2–4; pl. LXII,figs. 1–6) are 1–2 mm wide, with each segment having threeto four stomatal bands on the lower epidermis. Each bandconsists of two to six stomatal files.

Czekanowskia (subg. Vachrameevia) doludenkoaes Kiritch-kova and Samylina from the Early Jurassic of eastern Ka-zakhstan (Samylina and Kiritchkova 1991, p. 92, pl. IV, fig.3; pl. LXIV, figs. 1–5; text fig. 52) is similar to the new spe-cies in that the leaf segments are 0.75–1.25 mm wide. Themajor difference between them is that the species fromKazakhstan has stomata arranged in files on the lower epi-dermis. The leaf segments of Czekanowskia (subg. Vachra-meevia) hypostomatica Kiritchkova and Samylina (Samylinaand Kiritchkova 1991, p. 93, pl. I, fig. 4; pl. VI, fig. 12; textfig. 53) from the Late Jurassic of eastern Siberia are 1–1.5mm wide. Each segment has four to six stomatal bands onthe lower epidermis, and each band consists of two to fourstomatal files. Papillae are present on the periclinal walls.The leaf segments of Czekanowskia (subg. Vachrameevia) tes-lenko Kiritchkova and Samylina (Samylina and Kiritchkova1991, p. 94, pl. I, fig. 1; pl. III, fig. 8; pl. LXVI, figs. 1–4;text fig. 54) from the Middle Jurassic of eastern Siberia are0.8–1.5 mm wide. On the lower epidermis, each segment hasthree to five stomatal bands, and each band consists of twoto three stomatal files. Papillae are present on the periclinalwalls.

The leaf segments of Czekanowskia (subg. Vachrameevia)tomskiensis Kiritchkova and Samylina (Samylina and Kiritch-kova 1991, p. 95, pl. LXVII, figs. 1–4; text fig. 55) from theLate Jurassic of western Siberia are 1.5–2.5 mm wide. Eachsegment has three to four stomatal bands on the lower epi-dermis, and each band consists of two to three files near theleaf segment margin or four to five files in the center part ofthe segment. The size of stomatal complexes varies from 24to 42 mm long by 21 to 31 mm wide. The leaf segments ofCzekanowskia (subg. Vachrameevia) uzbekistanca Kiritchkovaand Samylina (Samylina and Kiritchkova 1991, p. 96, pl. II,fig. 13; pl. III, fig. 2; pl. XI, fig. 4; pl. XXI, fig. 5; pl. XLV, figs.6–9; pl. XLVIII, figs. 1–8) from the Middle Jurassic of centralAsia are 1–3 mm wide, with each segment containing three to

Fig. 4 SEM images of the upper and lower cuticle of Czekanowskia (subg. Harrisella) chinensis sp. nov. showing leaf epidermal features. A,

S012-27, inner surface of the upper cuticle showing a stomatal zone on the right and a nonstomatal zone on the left. Scale bar ¼ 100 mm. B, S012-

18, inner surface of the upper cuticle showing a stomata complex with two guard cells (g) surrounded by five subsidiary cells (s). Scale bar ¼ 10mm. C, S004.1-23, outer surface of the upper cuticle showing a stoma with papillate on subsidiary cells. Scale bar ¼ 10 mm. D, S012.1-2, inner

surface of the lower cuticle showing stomata arranged in bands with three to four longitudinal files and a nonstomatal zone in the middle. Scale

bar ¼ 100 mm. E, S012.1-21, inner surface of the lower cuticle showing pits on the subsidiary cell walls (s). Scale bar ¼ 10 mm. F, S012-5, innersurface of the lower cuticle showing a stoma complex of two guard cells (g) surrounded by five subsidiary cells (s) and unevenly developed

thickening on the periclinal walls and striation on the anticlinal walls. Scale bar ¼ 10 mm.

1189SUN ET AL.—JURASSIC CZEKANOWSKIA OF INNER MONGOLIA, CHINA

seven stomatal bands on the lower epidermis. Each band con-sists of three to seven stomatal files.

Wu et al. (2002) reported Czekanowskia (subg. Vachra-meevia) sp. from the Middle Jurassic of the Alashan area, In-ner Mongolia, China (Wu et al. 2002, p. 167, pl. XI, fig. 1b;pl. XVII, figs. 1–3), but only fragments of the lower epider-mis have been observed. Therefore, the distribution and arrange-ment of stomata on the leaves are unavailable to compare withthe new species.

Discussion

Abundant fossil material from Inner Mongolia demon-strates that Czekanowskia is a diverse and important mem-ber of the Middle Jurassic flora in northern China. Accordingto Samylina and Kiritchkova (1991, 1993), fossil leaves thatwere unequivocally assigned to Czekanowskia (subg. Czeka-nowskia) and Czekanowskia (subg. Vachrameevia) are firstfound in Later Triassic sediments (Norian-Rhaetic). The fact

Fig. 5 SEM images of the lower cuticle of Czekanowskia (subg. Harrisella) chinensis sp. nov. showing leaf epidermal features. A, S012-13,

outer surface of the lower cuticle showing a stomatal complex with papillae on subsidiary cells partially covering stomatal pit. Scale bar ¼ 10 mm.

B, S004.2-19, outer surface of the lower cuticle showing a stomatal complex with papillae on subsidiary cells covering most of the stomatal pit.

Scale bar ¼ 5 mm. C, S012.1-19, inner surface of the lower cuticle showing uneven thickenings on the periclinal walls of the subsidiary cells. Scalebar ¼ 10 mm. D, S004.1-1, inner surface of the lower cuticle showing uneven thickenings (shown as depressions) on the subsidiary cell walls. Scale

bar ¼ 10 mm.

1190 INTERNATIONAL JOURNAL OF PLANT SCIENCES

that six species have been reported from the Upper Triassicimplies that this group was less diverse at that time. At thebeginning of the Early Jurassic, the number of species beganto increase gradually, and Czekanowskia (subg. Harrisella)appeared. During the Middle Jurassic, the diversity of thesetaxa reached its maximum. From the beginning of the LateJurassic, the number of taxa was reduced remarkably as a re-sult of large-scale transgression from northern seas and ex-pansion of an arid climate. At the end of the Late Jurassic,Czekanowskia (subg. Harrisella) and Czekanowskia (subg.Vachrameevia) became extinct. The latest record of Czeka-

nowskia subgenus Czekanowskia was reported from the ear-liest Late Cretaceous sediments of the Upper Kolyma River(Samylina 1988) and Japan (Kimura and Okawara 1982).

Previous reports indicate that abundant Czekanowskialeaves have mainly been found in many localities of the LateTriassic and Early and Middle Jurassic coal-bearing sedi-ments in North China; unfortunately, most of the variousspecies assigned to the genus Czekanowskia are all basedon gross leaf morphological features except those from theJurassic of Northwest China (Wu et al. 2002). This reportdescribes two new species of two subgenera on the basis ofwell-preserved epidermal features from Inner Mongolia,China. Their occurrences significantly extend the strati-graphic and geographic distribution of Czekanowskia in theNorthern Hemisphere.

The age of the Zhaogou Formation, from which the speci-mens of the two new species were collected, has been ac-cepted as Middle Jurassic (Geological and Mineral ResourcesBureau of Inner Mongolia Autonomous Region 1991). Thediversity of fossil plants in this formation has not yet beenstudied systematically. Our current collection indicates thatthe flora of the Zhaogou Formation is quite rich and diverse.It contains ferns (Coniopteris, Eboracia, Hausmania, Raphae-lia, and Cladophlebis), cycads (Anomozamites, Pterophyllum,and Nilssonia), ginkgos (Ginkgo, Baiera), Czekanowskiales(Czekanowskia, Phoenicopsis, and Sphenarion) and conifers(Pityophyllum, Elatocladus, and Storgaardia). On the basis ofour preliminary analysis, most genera listed above also occur inthe Early and Middle Jurassic deposits in Eurasia. Some ofthem, including Coniopteris and Eboracia, are common com-ponents and are diverse in the Middle Jurassic, but they arerare in the Early Jurassic. Neocalamites belongs to the horsetailfamily and is an important component in many areas of Eura-sia during the Early Jurassic and Late Triassic. It has also beenfound in the Lower Jurassic Wudanggou Formation, but it isabsent in the Zhaogou Formation. The preliminary biostrati-graphic analysis of this flora indicates that its age is Middle Ju-rassic.

The discovery of the two new species in the Middle Juras-sic deposits in Inner Mongolia is also of paleogeographic andpaleoenvironmental significance. Various reports suggest thatthe genus Czekanowskia was mainly distributed in the warmtemperate and temperate areas, with seasonal temperaturevariations and humid climatic conditions during the Meso-zoic of the Northern Hemisphere (Vachrameev 1987, 1991).The characters of the leaf epidermis described in this articlealso imply a regional humid and warm climatic conditionwith seasonal temperature variations. These characters in-clude unevenly thickened periclinal and anticlinal walls ofepidermal cells that lack papillae, hairs, and trichomes andslightly sunken stomata below the surface of the subsidiarycells. The unevenly developed papillae on subsidiary cellsmay result from the seasonal temperature variations.

The occurrence of some taxa of cycads, though less diversethan in subtropical and tropical flora, also supports the factthat the regional climate condition was warm temperate, be-cause cycads are rarely found in cooler temperate floras suchas Siberia during the Mesozoic. Today, cycads grow mainlyin subtropical and tropical areas and a few in warm temper-ate regions.

Fig. 6 SEM images of the upper and lower cuticle of Czekanow-skia (subg. Harrisella) chinensis sp. nov. showing leaf epidermalfeatures. A, S012-19, inner surface of the upper cuticle showing

stomata arranged in band with two longitudinal files, the shape of

ordinary epidermal cells, unevenly developed thickenings on the

periclinal walls, and striation on the anticlinal walls. Scale bar ¼ 20mm. B, S012-9, inner surface of the lower cuticle showing striations on

ordinary epidermal cell walls. Scale bar ¼ 20 mm.

1191SUN ET AL.—JURASSIC CZEKANOWSKIA OF INNER MONGOLIA, CHINA

Fig. 7 Leaves of Czekanowskia (subg. Vachrameevia) shiguaiensis sp. nov. A, S005, specimen showing a bundle of linear leaves (arrows indicate thepositions where cuticle was removed for preparation). Scale bar ¼ 1 cm. B, S005-19, inner surface of the upper and lower cuticle. The central part is

the inside view of the upper cuticle, while the lower cuticle is on two lateral sides. Scale bar¼ 100 mm. C, S005-22, inner surface of the upper (left) and the

lower (right) cuticle, showing slight striations on the anticlinal walls. Scale bar¼ 20 mm. D, S005-17, outer surface of the upper cuticle. Note that palillaeandtrichomesare absent.Scalebar¼50mm.E, S005-6,outer surfaceof the uppercuticle.Note thatpapillae andtrichomesare absent.Scalebar¼10mm.

Sedimentological evidence also indicates that the InnerMongolian Jurassic climate was humid and warm. Lithologi-cally, the Zhaogou Formation is divided into three memberson the basis of our field investigation. The lower member,yielding abundant fossil plants and the Czekanowskia leavesdescribed in this article, consists of conglomerates, sandstones,siltstones, shales, and coal layers and some fossil bivalves. Themiddle member consists of sandstones, siltstones, and coalbeds, which are currently being mined, and also contain fossilplants. The upper part is composed of conglomerates, sand-stones, oil-shale, calcic shale, and marlite, yielding fossil fish,conchostracans, and insects. The analysis of sedimentary cyclesindicates that the Zhaogou Formation was formed in a fandelta containing fluvial and lacaustrine sediments.

Acknowledgments

We thank our colleagues from Jilin University, ProfessorXiuliu Mao, Xiangdong Peng, and Liren Cheng for helpingus collect many excellent specimens during the geologicalsurvey; Chuntian Li for photographing the specimens; An-ping Wang for help with SEM work at the Research Centerof Paleontology and Stratigraphy of Jilin; Fengxiang Liu forhelping us prepare the fossil cuticle; and three anonymousreviewers for their helpful suggestions and comments on themanuscript. This study was funded by the China GeologicalSurvey grant 70101209016, Specialized Research Fund forthe Doctoral Program of Higher Education grant, China1999018702, and Project 111, China.

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Fig. 8 SEM images of the upper and lower cuticle of Czekanowskia (subg. Vachrameevia) shiguaiensis sp. nov. showing leaf epidermal

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