Zhao et al.—New Jurassic Nilssoniopteris species from Xinjiang of China
base (Fig. 5.12), or the lamina tapers to a cuneate base (Figs. 3.2, 5.1). In the narrowly oblong leaves, both sides of the widest part run nearly parallel for a distance, gradually narrowing down- wards (Fig. 4.1–4.3). All laminae narrow from the widest part towards the apex slightly, and then contract quickly near the top to form a retuse apex 1–3mm deep (Figs. 3.1, 3.3, 4.3), or to have a pointed end 4mm high (Fig. 5.1), or to form a truncated apex (Fig. 4.2). The midrib is straight, having a width of 1.5–2.5mm. The
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midrib is ridged on the abaxial surface but relatively flat on the adaxial surface, sometimes shows irregularly transverse wrin- kles (Fig. 5.2). The wrinkles can be obvious or not depending on bedrock grain size. The lamina is attached laterally to the midrib and does not cover it. The petiole is 0.7–1.5cm long and 2–3mm thick. The secondary veins are slender and even inconspicuous
in most specimens. They arise from the midrib at angles of 80°–90°. The veins are simple or forked once or twice, and the location of bifurcation is not fixed. In a few specimens, a few veins fork and then merge to form a closed loop (Fig. 5.8), or two adjacent veins merge and then disjoin again (Figs. 5.9, 5.10, 8.9). Vein density varies at different distances from midrib in the same leaf and differs among different leaves. In some leaves, vein density increases from ~16 per cm near the midrib to ~23 per cm near the margin; while in others, it can increase from ~20 per cm near the midrib to ~34 per cm near the margin (Fig. 8.10). Vein density of narrowly oblong leaves is generally higher than that of other leaf shapes. Some young leaves are preserved along with the above-
mentioned mature leaves. They show variety in their macro- morphology (Fig. 8.7, 8.8). For example, a narrowly oblong young leaf is 6.5cm long and 2 cm wide with its apex short pointed (Fig. 5.3 [b]) while another narrowly oblong young leaf is 7 cm long and 2 cm wide, having a retuse apex (Fig. 5.11). Two elliptic young leaves are ~4.5cm long and 2.5cm wide (Fig. 5.5). One of them (Fig. 5.5 [left]) shows sparse veins having a vein density of 11 per cm near the midrib while the other (Fig. 5.5 [right]) has a vein density of 19 per cm near the midrib. Because these young leaves: (1) often are preserved together with each other, (2) often are preserved together with mature leaf specimens of N. hamiensis n. sp. (3) have their leaf morphology showing gradual but continuous changes, and (4) exhibit cuticular features similar to those of the mature leaves of N. hamiensis n. sp. we interpret them to be young leaves of the current new species. The adaxial cuticle is thin. Epidermal cells along veins are
not different from those between veins in some leaves under a transmitted-light microscope (Fig. 6.2), although in some other leaves, they might be slightly different (Figs. 6.1, 7.1). The epidermal areas along veins are ~40–80 μm wide, composed of ~2–4 rows of rectangular or elongated cells while the epidermal
areas between veins are 300–650 μmwide, consisting of square, rectangular, or more or less isodiametric cells. In addition, cells between veins are generally shorter and wider than those along the veins. Epidermal cell outlines are distinctly recognizable and mostly regular in arrangement. Their anticlinal walls are wavy to finely sinuous (Figs. 6.2, 7.2). Stomata are absent. Trichome bases, consisting of a single oval or round cell with a thickened ring, occur along veins and between veins (Figs. 6.2, 6.3, 7.3). The density of trichome bases differs among leaves. The abaxial cuticle is nearly equal in thickness to the adaxial
one. Epidermal areas along veins are obviously different from those between veins (Fig. 6.4–6.6): those along veins are 70– 100μm wide, composed of about 2–4 rows of rectangular or elongated cells while those between veins are 300–740μmwide, consisting of irregularly shaped cells. Under a transmitted-light microscope the epidermal cell outlines are clear and the anticlinal walls of these cells are generally wavy. Laminae are hypostomatic. Stomata are scattered mainly
in the areas between veins on the abaxial surface. Stomatal bands are obviously wider than bands along veins without stomata (Figs. 6.7, 8.11, 8.12). The density range of stomata is 25–55 per mm2:25–35 per mm2 of narrowly elliptic to oblanceovate leaves (Figs. 6.4, 8.11) and 40–55 per mm2 of narrowly oblong leaves (Figs. 6.5, 8.12). Stomata are irregularly oriented, being parallel, vertical, or oblique to veins (Figs. 6.7, 6.8, 7.4). They are syndetocheilic, mainly near-rectangular to elliptic in shape and 25–30 × 50–60 μm in size (Figs. 6.9, 6.10, 6.13, 7.5, 7.6). Sometimes they can be nearly square to rounded, ~35 µm in diameter (Figs. 6.11, 7.8). From the external view, subsidiary cells are flat (Fig. 7.19, 7.20). The two polar anticlinal walls of subsidiary cells are usually parallel, and the exceptional polar anticlinal walls extend outwards to form an angular shape. The two distal anticlinal walls are usually semicircular in shape. Guard cells are sunken below subsidiary cells with cutinized inner wall thickenings (Fig. 7.5, 7.7). Numerous trichome bases of 1–4 cells of varied shapes
occur along veins and between veins of the abaxial surface. Trichome bases are rounded or elliptic (Fig. 7.18, 7.19) and are 20–50 μm in diameter. The unicellular trichome bases may or may not have thickened anticlinal walls. Multicellular trichome bases consisting of 2–4 cells (Fig. 7.10–7.12) have their anticlinal walls sometimes ridged and sometimes strongly cutinized and surrounded by radial thickenings on the periclinal walls. The internal sculpture of anticlinal walls of trichome base cells is usually similar to that of the neighboring epidermal cells under SEM, although sometimes the anticlinal walls of the former can be slightly more thickened and straighter than those of the ordinary epidermal cells. The density range of trichome bases is 12–40 per mm2:12–25 per mm2 of narrowly elliptic to oblanceovate leaves (Fig. 8.11) and ~35 per mm2 of narrowly oblong leaves (Fig. 8.12).
Figure 5. Nilssoniopteris hamiensis Zhao and Deng, n. sp. from the Xishanyao Formation of the Sandaoling Coal Mine, Xinjiang Uygur Autonomous Region, China. (1) An oblanceovate leaf with a short pointed apex and a cuneate base, SDL-98-4-05; (2) details of two midribs; transverse wrinkles are shown on the impression of the adaxial side and a longitudinal groove shown on the impression of the abaxial side, SDL-99-070; (3) a fragment on the left and a young leaf with narrowly oblong in outline and a short pointed apex on the right, SDL-98-0208; (4) a fragment with a retuse apex, SDL-99-080; (5) two young leaves with elliptical outline, SDL-98-0208; (6) a leaf with an obtuse-rounded base, SDL-99-037; (7) middle part of a leaf, SDL-98-4-02; (8) details of veins, showing a vein fork once and then anastomose (indicated by the arrow), SDL-99-045; (9) details of veins, showing two adjacent veins merge to be one vein and then disjoin again (indicated by the arrow), SDL-99-045; (10) details of veins, showing two adjacent veins merge to be one vein and then disjoin again (indicated by arrows), SDL-99-070; (11) a young leaf with narrowly oblong in outline, SDL-99-075; (12) lower part of a leaf with a rounded base, SDL-99-075. Scale bars=5mm in (8, 9) and=1 cm in the others.
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