Zhao et al.—New Jurassic Nilssoniopteris species from Xinjiang of China
the figures in Lundblad (1950), its blunt-rounded laminar apex is clearly different from the retuse, truncated, or short pointed apex of our specimens. Another species that is more or less comparable with the
present species is N. kokalensis from the Early Jurassic of western Kazakhstan (Kiritchkova, 2000; Kiritchkova and Nosova, 2012), which also possesses numerous trichome bases having cutinized thickenings on the abaxial epidermis. However, its stomatal bands are slightly narrower than nonstomatal bands, its stomata are smaller in size than ours, and its adaxial epidermis lacks trichome bases. These features make them different from our leaves. In addition, the stomatal densities of our narrowly elliptic
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to oblanceovate leaves (25–35 per mm2) and the narrowly oblong leaves (40–55 per mm2) are quite different from each other. Due to the fact that: (1) these two leaf shapes have continuous intermediate shaped specimens in the flora, (2) they sometimes are even preserved on the same hand specimen, and (3) they share almost all micromorphological and anatomical characteristics, we interpret them to belong to the same species. The obvious stomatal density difference might be the result of different ecological adaptations, which might have been caused by their different positions on the same plant or different plants growing under different microenvironments.
Nilssoniopteris crassiaxis Zhao and Deng, new species Figures 9–12
1911 Taeniopteris vittata; Seward, p. 16, pl. 3, figs. 30, 31.
Holotype.—SDL-98-L2, from the Middle Jurassic Xishanyao Formation at Sandaoling Coal Mine, Xinjiang Uygur Autono- mous Region, China (Fig. 9.13).
Paratypes.—SDL-98-4-11 (Fig. 9.1), SDL-98-409 (Fig. 9.3), SDL-98-4-13 (Fig. 9.6), SDL-98-L14 (Fig. 9.10), and SDL-98- L1 (Fig. 9.11).
Diagnosis.—Leaves petiolate, entire-margined, long strap- shaped, but with the widest part at the apical portion. Petiole stout. Lamina gradually and very slowly narrowing from the widest part to the base while narrowing towards the apex more quickly. Leaf base cuneate, apex likely obtuse to obtuse- rounded. Midrib at leaf base stout, accounting for one-third to one-half width of leaf base, tapering gradually towards leaf apex. Midrib surface bearing irregular transverse corrugations.
Lamina attached to the adaxial side of midrib but leaving the central part exposed. Secondary veins thin, conspicuous, simple or forked once, twice, or even three times, with a few veins forking and then merging and a few others merging with their neighboring veins. Leaf hypostomatic. Epidermal areas along veins and between veins distinct on both surfaces. Epidermal cells on the adaxial surface square, rectangular, or more or less isodiametric, with anticlinal walls sinuous, U-shaped, or Ω-shaped. Epidermal cells along veins on the abaxial surface rectangular or elongated, between veins irregularly shaped, with anticlinal walls strongly sinuous, U- or Ω-shaped. Stomata syndetocheilic, mostly vertical or oblique to veins but occasionally parallel to veins. Trichome bases consisting of 1–3 cells occurring numerously along veins and between veins of the abaxial epidermis. Epidermal cells on the abaxial surface of midrib having straight anticlinal walls, with numerous trichome bases present.
Occurrence.—The Xishanyao Formation at Sandaoling Coal Mine, Xinjiang Uygur Autonomous Region, China.
Description.—This new species is represented by ~20 leaf- bearing specimens in our collection. The leaves are long strap- shaped, entire-margined, and petiolate. Among our collection, the longest leaf reaches a length of ~22 cm, but with only the lower region of the leaf preserved (Fig. 9.3). Based on the shape of the preserved part, the full length might be ~50 cm. Its widest preserved part is at the apical portion of the leaf, which reaches up to 7.5cm wide (Fig. 9.1, 9.2). The lamina gradually and very slowly narrows from the widest part down to the petiole (Fig. 9.3, 9.6, 9.10, 9.13), and the width of the leaf is ~4.5cm at a distance of ~22cm from the base and ~2cm at a distance of ~6cm from the base (Fig. 9.3). The lamina tapers to a cuneate base (Fig. 9.3, 9.11). The lamina narrows from the widest part towards the apex more quickly than towards the base, from 6.6cm wide to 3.5cm wide at a distance of ~6cm (Fig. 9.2). The petiole is stout, ~3cm long and 9mm wide (Fig. 9.11). The midribs of these specimens are also stout with a width of 5–8mm at the leaf base, accounting for one-third or even one-half of the leaf base width (Fig. 9.3). The midrib width gradually decreases acropetally. Irregular transverse corruga- tions are always observed on the midrib on the impressions (Fig. 9.4). The lamina is attached to the adaxial side of the midrib, but leaves the central part of the midrib exposed. The exposed width is 1–2.5mm, wider below and thinner above, with the thinnest near the widest part of the leaf (Fig. 9.5).
Figure 7. Nilssoniopteris hamiensis Zhao and Deng, n. sp. from the Xishanyao Formation of the Sandaoling Coal Mine, Xinjiang Uygur Autonomous Region, China: (1, 2) internal view of adaxial cuticle; (the cuticles were from the specimen shown in Fig. 5.7); (1) epidermal areas along veins and between areas; scale bar=100 μm; (2) epidermal cells between veins; scale bar=50 μm; (3) external view of adaxial cuticle, showing trichome bases of adaxial cuticle (the cuticle was from the specimen shown in Fig. 5.7); scale bar=50 μm; (4–12) internal view of abaxial cuticle (the cuticles were from the leaf shown in Fig. 5.3 [a]): (4) areas along a vein and distribution of stomata; scale bar=100 μm; (5) one rectangular stoma; scale bar=20 μm; (6) two stomata; scale bar=20 μm; (7) one stoma with sunken guard cells and cutinized inner margins of guard cells; scale bar=20 μm; (8) one round stoma and one rectangular stoma from side view; scale bar=20 μm; (9) two stomata and one trichome base (indicated by the black arrow); scale bar=50 μm; (10) three stomata and one trichome base consisting of two cells (indicated by the black arrow); scale bar=50 μm; (11) three stomata and one trichome base consisting of three cells (indicated by the black arrow); scale bar=50 μm; (12) three stomata and two trichome bases consisting of four cells (indicated by black arrows); scale bar=50 μm; (13) internal view of adaxial cuticle on the midrib, showing epidermal cells and about two rows of stomata (indicated by white arrows); scale bar=100 μm; (14) external view of adaxial cuticle on the midrib, showing trichome bases on the central area (indicated by black arrows) and rows of stomata on one side (by white arrows); scale bar=100 μm; (15) internal view of abaxial cuticle on the midrib, showing epidermal cells and one row of stomata (indicated by white arrows); scale bar=100 μm; (16) external view of abaxial cuticle on the midrib, showing trichome bases; scale bar=100 μm; (17–20) external view of abaxial cuticle; (17) areas along a vein and trichome bases along and between veins; scale bar=100 μm; (18) two trichome bases; scale bar=50 μm; (19) one trichome base and one stoma (indicated by the white arrow); scale bar=20 μm; (20) one stoma; scale bar=10 μm.
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