Zhao et al.—New Jurassic Nilssoniopteris species from Xinjiang of China On the middle portion of the adaxial surface of the midrib,
cells are near square or more or less isodiametric, with many scattered trichome bases (Fig. 6.14). Towards both sides, epidermal cells on the midrib become increasingly elongated (Fig. 7.13). Two files of stomata can be observed along each side of midrib (Figs. 6.14, 6.15, 7.13, 7.14). Cells on the abaxial surface of the midrib are rectangular or elongated and are longitudinally arranged, with many scattered trichome bases. One file of stomata is distributed on one side of the midrib (Figs. 6.16, 7.15, 7.16). Anticlinal walls of cells on both surfaces of the midrib are straight.
Etymology.—The specific epithet “hamiensis” is a latinization of the Chinese Pinyin name of the discovery location, Hami City.
Remarks.—Based on the entire-margined laminae, sinuous anticlinal walls of epidermal cells, and syndetocheilic stomata, the present specimens can be undoubtedly assigned to the genus Nilssoniopteris. One of the leaves in the present collection was previously assigned to N. vittata without detailed cuticular features (Deng et al., 2010). However, newly prepared cuticles not only allowed us to align the specimen with others, but separate this set of specimens from all known species. Besides some macromorphological differences, our specimens are mainly distinguishable from known species in the following combined suite of characteristics: (1) they have anticlinal walls of their cells finely sinuous on the adaxial epidermis; (2) they have unicellular trichome bases, oval or round, on the adaxial epidermis; and (3) they have numerous trichome bases of 1–4 cells with various shapes on the abaxial epidermis. The Supplementary Data Set displays the main comparison
of our two new species with all 43 Jurassic species worldwide. Among those 43 species, the one most similar to the present new species in leaf form, leaf size, cuticular feature, and geological age is N. major, which is an important bennettitalean species from the Middle Jurassic flora of Yorkshire, England (Harris, 1969). For example, cuticular analysis of Harris’s specimens demonstrated that its trichome bases are also usually present on the abaxial epidermis, and the number of their basal cells is 1–4, similar to those of our specimens. The densities of stomata and trichome bases of Harris’s specimens are similar to those of our narrowly elliptic and oblanceovate leaves. Leaf form and leaf size of Harris’s mature and young leaves resemble those of our mature narrowly elliptic and oblanceovate leaves and our young narrowly oblong leaves. In addition, line drawings of Harris’s specimens also show vein anastomosis. However, our
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specimens are different from those of N. major in the following ways: (1) the lower parts of Harris’s ovate-lanceolate leaves narrow slightly and then end abruptly, whereas in our narrowly elliptic and oblanceovate leaves they more commonly taper gradually towards the base; (2) oblancelate and narrowly oblong leaves are lacking in Harris’s specimens, but common in our collection; (3) the leaf margins of N. major have minute teeth, which are not observed in our specimens; (4) the density of secondary veins of N. major is 6–12 per cm, which is considerably lower than that of most of our specimens; and (5) trichome bases are lacing on the adaxial epidermis of N. major while existing on that surface of our specimens. These differences provide us the confidence to separate our specimens from N. major. Nilssoniopteris vittata, described by Harris (1969) from
Yorkshire (now referred to as N. solitaria by Cleal and Rees, 2003; Cleal et al., 2006; Van Konijnenburg-van Cittert et al., 2017; Pott and Van Konijnenburg-van Cittert, in press), is another species showing some similarities to our specimens. However: (1) in N. solitaria, the leaves are linear-lanceolate in outline and rarely up to 3cm wide, which is much narrower than most of our specimens; (2) the anticlinal walls of adaxial epidermal cells of N. solitaria are coarsely sinuous (ridges extend from folds almost to middle of cell), which are different from the finely sinuous walls of most cells of our specimens; and (3) trichome bases on the abaxial epidermis of N. solitaria are composed of 1–2 cells, while our specimens have 1–4 cells. These differences prevent us from allocating our specimens to N. solitaria. One of the typical features of our specimens is the presence
of numerous and conspicuous trichome bases of 1–4 cells with various shapes on the abaxial epidermis. Similar trichome bases have been reported in N. glandulosa (Florin, 1933b) and Nilssoniopteris sp. b (Lundblad, 1950) from the Early Jurassic Lias flora of Sweden. Florin’s leaves lack apices and bases and are 1–4.5cm wide, which were considered to be linear- lanceolate to lanceolate. The secondary vein density of leaves that are l–2.5cm wide is 17–22 per cm (Florin, 1933b, pl. 1, figs.
4, 6) and 13 per cm in leaves ~4cm wide (Florin, 1933b, pl. 1, fig. 2). They are respectively lower than that of our narrowly oblong leaves and that of our narrowly elliptic to oblanceovate leaves. In addition, the number of trichome basal cells of
N. glandulosa is up to 5–6 (Florin, 1933b, pl. 2, figs. 2, 3, text- fig. 5), which is different from 1–4 of our species. Lundblad’s specimen (Nilssoniopteris sp. b, Lundblad, 1950) is only preserved with the apical portion of a leaf. Although its trichome bases bear a certain resemblance to ours, based on
Figure 6. Nilssoniopteris hamiensis Zhao and Deng, n. sp. from the Xishanyao Formation of the Sandaoling Coal Mine, Xinjiang Uygur Autonomous Region, China. (1–3) Adaxial cuticle: (1) areas along veins and between veins (the cuticle was from the specimen shown in Fig. 5.7); scale bar=500 μm; (2) epidermal cells and trichome bases along and between veins (the cuticle was from the specimen shown in Fig. 5.4); scale bar=200 μm; (3) epidermal cells and trichome bases (the cuticle was from the specimen shown in Fig. 4.2); scale bar=100 μm; (4–13) abaxial cuticle: (4) epidermal areas along two veins and between veins (the cuticle was from the specimen shown in Fig. 3.3); scale bar=500 μm; (5) epidermal areas along two veins and between veins (the cuticle was from the specimen shown in Fig. 4.2); scale bar=200 μm; (6) epidermal areas along three veins and between veins (the cuticle was from the specimen shown in Fig. 4.3); scale bar=200 μm; (7) stomata between veins and trichome bases along and between veins (the cuticle was from the specimen shown in Fig. 3.3); scale bar=200 μm; (8) stomata between veins and trichome bases along and between veins (the cuticle was from the leaf shown in Fig. 5.3 [a]); scale bar=100 μm; (9) three stomota and one trichome base; scale bar=50 μm; (10) one stoma and two trichome bases; scale base=50 μm; (11) two stomota and one trichome base; scale bar=50 μm; (12) one stoma and one trichome base; scale bar=50 μm; (13) one stoma and one trichome base; scale bar=50 μm; (14, 15) adaxial cuticle of the midrib: (14) epidermal cells and trichome bases of the central area of a lamina (notice the epidermal cells and about two rows of stomata on each side of the midrib); scale bar=200μm; (15) enlargement of stomata (indicated by white arrows) and trichome bases (by black arrows); scale bar=100μm; (16) abaxial cuticle on the midrib, showing epidermal cells and trichome bases, and stomata on one side (indicated by the white arrow); scale bar=200μm.
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