Pseudoctenis Seward, 1911 emend. Harris, 1964

Pott, Christian, Mcloughlin, Stephen & Lindström, Anna, 2010, Late Palaeozoic foliage from China displays affinities to Cycadales rather than to Bennettitales necessitating a re-evaluation of the Palaeozoic Pterophyllum species, Acta Palaeontologica Polonica 55 (1), pp. 157-168 : 159-163

Genus Pseudoctenis Seward, 1911 emend. Harris, 1964

Type species: Zamites eathiensis Richards, 1884 ; from the Jurassic of Scotland .

Remarks.—The cycadalean foliage genus Pseudoctenis is a common element of several Mesozoic (Rhaetian–Jurassic) floras in Europe ( Seward 1911, 1917; Harris 1932, 1950, 1964; Pott et al. 2007b). Seward (1911) introduced the genus for Zamites − type leaves from the Jurassic of Sutherland, Great Britain. Although Ctenis and Pseudoctenis are similar in macromorphology, Seward (1911) noted that they are easily distinguishable based on the occurrence of anastomoses in the venation of Ctenis , an interpretation with which Harris (1950) concurred. Nevertheless, historically, Pseudoctenis has often been used in an arbitrary manner because no valid generic diagnosis existed. Furthermore, numerous foliage specimens have been accommodated in genera such as Pterophyllum , Ctenophyllum , and Zamites over many years, although they better matched the characters of Pseudoctenis . This changed when Harris (1932) described the epidermal features of several Pseudoctenis species from the Rhaetian of Greenland. The epidermal anatomy established the cycadalean affinities of Pseudoctenis based on the presence of cyclocytic (“haplocheilic”) stomata. Harris (1932, 1964) provided a diagnosis for Pseudoctenis that included both macromorphological and epidermal characters. The earliest confirmed representatives of the genus occur in the Carnian of Lunz, Austria ( Pott et al. 2007b).

doi:10.4202/app.2009.0070

Pseudoctenis samchokense ( Kawasaki, 1934) nov. comb.

Figs. 2–4.

1931 Pterophyllum samchokense nom. nud.; Kawasaki 1931: pl. 86: 260.

1934 Pterophyllum samchokense sp. nov.; Kawasaki 1934: 197, no illustration.

1939 Pterophyllum pruvostii sp. nov.; Stockmans and Mathieu 1939: 93, pl. 21: 2, 2a, 3.

1974 Pterophyllum pruvostii Stockmans and Mathieu, 1939 ; Gu and Zhi 1974: 144, pl. 114: 1, 2.

2006 Pterophyllum pruvostii Stockmans and Mathieu, 1939 ; Sun 2006: 385, no illustration.

Basionym : Pterophyllum samchokense Kawasaki, 1934 .

Type material: Holotype: specimen figured by Kawasaki (1931) on pl.

86: 260 (repository and accession number not recorded). Epitypes:

specimens NRM S 141652 and NRM S 141653 ( Fig. 3C, 3F).

Type locality: Sanchoku (Samchok) district , South Korea (Chosen) .

Type horizon: Jido Series, Heian Group.

Remarks.—The species was originally established on a single specimen and compared to Pterophyllum daihoense by Kawasaki (1934). However, another comment by the author in the same paragraph, later supported by Sze (1936), illustrates that these taxa can not be regarded as conspecific because Pt. daihoense includes leaves with laminae that are partly not divided into segments, especially in the distal portion of the leaf. Specimen NRM S 141652 is chosen as an epitype, because it provided the cuticular details on which the new combination of the species is based.

Material/repository.— 26 specimens from the palaeobotanical collections in the NRM . From Yangjialiang: S141640 , S141648 , S141650 – S141655 ; from Damugou: S143500−02 , S143501 , S143502 , S143503 a, S143503 b, S143504 , S143505 , S143506−01 , S143506−02 , S143507 , S143508−01 , S143509 , S143510 , S143511−01 , S143511−02 , S143512 , S143513−01 ; from Linxi: S146368 .

Emended diagnosis.—Frond pinnate, rachis roughly striate, leaflets attached laterally and almost perpendicularly to the rachis, distinctly separated, never confluent, slender and unequal in width, gradually narrowing into the bluntly pointed apices, slightly narrowing near the base and a little dilated at the attachment to the rachis, basipetal margin slightly decurrent; veins forked at the base and commonly just distal to the base; the marginal veins arching parallel to the margins of the leaflets and the middle ones being straight; leaves hypostomatic, epidermal cells isodiametric polygonal to broadly elongate, cell walls straight, stomata surrounded by 5–7 subsidiary cells (emended after Kawasaki 1934).

Description.—Leaves are petiolate, impari−segmented, regular, oblong to broadly oval in outline ( Fig. 2A–C), obtusely rounded at apex, up to 24 cm long and 22 cm wide (incomplete leaves). The petiole is prominent, but incomplete on all Ą specimens ( Fig. 2B; arrow). Besides these large leaves, some very small leaves occur ( Fig. 3D) that reach only 5 cm long but display identical leaf architecture apart from narrower rachides. The lamina is subdivided into numerous long and narrow, parallel−sided to ensiform leaflets, which are oppositely to sub−oppositely positioned ( Fig. 2A–E). The length of the individual leaflets varies depending on the position in the leaf; leaflets are up to 92 mm long and 5–11 mm wide. Leaflet length seems to increase slightly toward the middle of the leaf, and then gradually decrease toward the leaf tip ( Fig. 2C). The leaflets are only slightly constricted basally; the basipetal margin is slightly decurrent ( Fig. 3B; arrows). Leaflet apices are obtusely to acutely rounded ( Fig. 3E). The distance between the individual leaflets is regular within a single leaf but may vary between leaves of this species.

The leaflets are inserted laterally on the prominent and longitudinally striate rachis ( Fig. 3B, E, F). The distal leaflets are arched towards the apex and form a rounded leaf apex ( Figs. 2B, 3A). Numerous parallel veins enter each leaflet and usually bifurcate once close to the leaflet base ( Fig. 3B, C). In some cases, additional bifurcations occur in the proximal portion of the leaflet. Veins positioned close to the lateral leaflet margins do not fork. Cuticles are very thin, brittle and poorly preserved. The leaves are probably hypostomatic; costal and intercostal fields are distinguishable on the abaxial side of the leaf. Stomata are restricted to the intercostal fields ( Fig. 4C 1 , C 2). The adaxial cuticle is slightly thicker than the abaxial cuticle ( Fig. 4A, C 1 ).

Few details are available for the adaxial cuticle: epidermal cells are polygonal, elongate to isodiametric in outline, 40–100 µm long and 30–45 µm wide. Anticlinal and periclinal cell walls are smooth. Stomata, papillae and/or hair bases are absent ( Fig. 4A).

In the abaxial cuticle, costal fields are composed of 6–8 rows of epidermal cells. The cells above the veins are polygonal, elongate to isodiametric, 30–110 µm long, 30–40 µm wide, and possess delicate walls. Anticlinal cell walls are usually straight and periclinal walls are smooth; papillae are absent. Intercostal fields are 200–380 µm wide, with isodiametric polygonal to broadly rectangular cells. Epidermal cells are 30–80 µm long and 30–55 µm wide ( Fig. 4C 1 , C 2). Anticlinal cell walls are straight. Stomata ( Fig. 4B 1 –B 3, C 3) are cyclocytic (“haplocheilic”), probably slightly sunken, and up to 110 µm in diameter. Pores are orientated almost perpendicularly to the veins ( Fig. 4C 1 , C 2; arrows). Stomatal complexes incorporate 5–7 rectangular subsidiary cells that are arranged in a circle around the pit ( Fig. 4B 1 , B 2); some stomata appear to be surrounded by a weakly defined second ring of subsidiary cells. The guard cells possess heavily cutinised central portions of the dorsal walls, whereas the polar ends are weakly cutinised ( Fig. 4B 1 , B 2, C 3).

Discussion.—This foliage type is assigned to Pseudoctenis because essential macromorphological features (e.g., the segmented architecture of the leaf, the lateral and perpendicular insertion of the almost parallel−sided leaflets, and the striate rachis) correspond well to those evident in typical representa−

doi:10.4202/app.2009.0070

tives of the genus ( Harris 1964; Pott et al. 2007b). In addition, the venation is similar, especially with respect to the parallel lateral veins that fork near their base. Furthermore, the epidermal anatomy, characterised by cyclocytic (“haplocheilic”) stomata, justifies accommodation of this species in Pseudoctenis ( Harris 1964; Pott et al. 2007b) and, therefore, in the Cycadales .

Cycadales range from the Permo−Carboniferous to present. Cleal (1993) gave a short overview of their temporal distribution and stated that the first unequivocal cycads derive from the Early Permian of Taiyuan (Shanxi series) in China ( Gao and Thomas 1989). We agree with Cleal (1993) who suggested treating several doubtful Carboniferous and Early Permian fossils (for details see Cleal 1993) as precursors of the Cycadales rather than regarding them as true cycads. The fossils described here also come from the latest Carboniferous–Early Permian of China, some of them from close to the source of the early cycads described by Gao and Thomas (1989; see Fig. 1 ) and thus rank amongst the earliest cycads. The early cycadalean record of Gao and Thomas (1989) is now supported by unequivocal cycadalean foliage from coeval deposits of this region.

Stratigraphic and geographic range.—Latest Carboniferous to Early Permian of China (Hebei, Shanxi) and South Korea (Sanchoku).

Figures

Fig. 1. Map of NE China and Korea showing the localities from which Pseudoctenis samchokense fossils have been collected (grey symbols) and the locality from which Primocycas chinensis fossils have been described (black symbol).