Nilssonia mirovanae, Čepičková & Kvaček, 2020

Čepičková, Jana & Kvaček, Jiří, 2020, Two Cycads Nilssonia Mirovanae Sp. Nov. And Pseudoctenis Babinensis J. Kvaček From The Cenomanian Of The Bohemian Cretaceous Basin (The Czech Republic) As Indicators Of Water Stress In The Palaeoenvironment, Fossil Imprint 76 (2), pp. 315-324 : 317-318

Nilssonia mirovanae sp. nov.

Pl. 2, Figs 1–9

H o l o t y p e. NM-F 4698, designated here, housed in the National Museum, Prague, the Czech Republic (Pl. 2, Figs 1–9).

P l a n t F o s s i l N a m e s R e g i s t r y N u m b e r:

PFN001825.

E t y m o l o g y. The generic name is derived from the name of Jaromír (Miro) Váňa, who collected plant fossils in Pecínov quarry during his long-term service for the National Museum.

T y p e l o c a l i t y. Pecínov quarry, 50 km west of

Prague, the Czech Republic

T y p e h o r i z o n. Peruc-Korycany Formation, unit 1.

A g e. Cenomanian, Late Cretaceous.

D i a g n o s i s. Isolated strap-like entire-margined pinna fragment, venation running parallel to pinna margin, veins simple. Pinna hypostomatic, adaxial cuticle bearing elongate, rectangular ordinary cells, straight to slightly wavy anticlinal walls. Each ordinary cell bearing a pronounced ridge in its central part. Abaxial cuticle consisting of costal and intercostal zones, costal zones built by elongate, rectangular ordinary cells of the same type as those on the adaxial side; intercostal zones consisting of isodiametric to shortly elongate ordinary cells. Stomata, arranged in rows, haplocheilic surrounded with 4–6 (7) subsidiary cells each bearing a papilla, overhanging the stomatal pit; guard cells sunken. Stomatal axes orientated parallel to pinna margin. Ledges of dorsal thickenings of guard cells pronounced.

D e s c r i p t i o n. The holotype, and only known specimen, is a leaf compression – pinna fragment from a larger pinnate leaf (Pl. 2, Fig. 1). The specimen is a strap-shaped fragment of an entire-margined pinna. It is symmetric, 61 mm long and 6 mm wide. Veins are simple, running parallel to pinna margin. Venation density is 2–3 veins per mm.

The leaf is hypostomatic. Its adaxial cuticle comprises elongated rectangular ordinary cells, 40–90 µm long and 10–25 µm wide. Anticlinal walls are straight, rarely slightly wavy; their thickness is 4–6 µm (Pl. 2, Figs 6, 8). The abaxial cuticle consists of costal and intercostal zones (Pl. 2, Figs 2–5). The width of the costal zones is 200 µm, the intercostal zones 220 µm. The costal zones are formed by elongate ordinary cells, similar to those on the adaxial cuticle. The outer surfaces of the costal zones show parallel ridges (Pl. 2, Figs 3, 5). The intercostal zones consist of isodiametric to slightly elongated ordinary cells, 40–80 µm long and 10–20 µm wide (Pl. 2, Figs 2, 4). The periclinal wall of ordinary cells is smooth, showing parallel ridges, its thickness varies from 5 to 10 µm. The intercostal zones consist of three to four rows of stomata. Stomatal rows are separated by 1–3 ordinary cells (Pl. 2, Figs 2, 4, 9). The stomatal axes are oriented parallel to the pinna margin (Pl. 2, Fig. 9). The anticlinal walls are nearly straight or slightly bent. The stomata are haplocheilic (Pl. 2, Figs 4, 9), surrounded with 4–6 (7) subsidiary cells 20–60 µm long and 15–30 µm wide. They are sunken in stomatal chambers 25–30 µm long × 5–20 µm wide. Each subsidiary cell shows externally 3–6 (7) large papillae. The papillae surround the stomatal chamber from the outside (Pl. 2, Figs 5, 7).