Bjuvia sp.

Flores-Barragan, Miguel Angel & Leon, María Patricia Velasco-de, 2020, New records of Bjuvia and Nilssonia from the Permian of Mexico, Palaeontologia Electronica (a 28) 24 (3), pp. 1-17 : 3-8

cf. Bjuvia sp.

Figure 3

Material. CFZ-MTZ540, 551, 583.

Locality. Coatepec.

Description. Entire lamina, lanceolate, with entire margins, the rachis is prominent and longitudinally striate; veins are fine, numerous, simple, and emanate perpendicularly from the rachis. Irregular to square and/or rectangular epidermal cells have generally straight walls. The stomata are arranged in irregular rows; stomatal apparatus is protected by simple digitate papillae.

Given the large size of the lamina, all specimens are preserved as fragments, with the bestpreserved specimen measuring 15.0 cm in length and 18.55 cm in width at the mid-part ( Figure 3A ). The width of the leaf gradually decreases towards the apex and the base ( Figure 3B ). The shape of both is unknown. A rachis running along the lamina is longitudinally striated and 0.55 cm wide ( Figure 3C ). The leaf is laterally inserted into the rachis. The veins are perpendicularly inserted into the rachis. This venation is simple and has a density of 33 to 40 veins per centimeter in the proximal part to the margin ( Figure 3D ); the number of veins is constant along the entire lamina.

In the adaxial cuticle, the epidermal cells are rectangular to irregular in shape 80 to 90 µ long and 8 to 10 µ wide, with straight to slightly undulated anticlinal walls, 1 to 2 µ thick ( Figure 3E ). Crest distance is 6 to 8 microns, with a height of 3 microns. The epidermal cells are arranged parallel to the venation and also exhibit simple trichomes of up to 15 microns in length ( Figure 3I ).

In the abaxial cuticle, there are also irregular to square and/or rectangular epidermal cells, with straight anticlinal walls and a size between 50 and 100 µ ( Figure 3F ). The stomatal aperture is 10 to 15µ wide with 6-7 subsidiary cells on both sides surrounding the stoma. Four papillae are observed, which protrude from the stomatal aperture ( Figure 3G and J ). The stomata are arranged in irregular rows ( Figure 3H ).

Remarks. Entire leaves attached to a central rachis that lack epidermal and reproductive characters are generally located in the fossil taxon Taeniopteris (Van Konijnenburg-van Cittert et al., 2017). In this case, we observe seven subsidiary cells. The shape of the epidermal cells, the presence of trichomes, and the absence of dichotomies in the veins also suggest Bjuvia . Nevertheless, it is necessary to obtain better preserved material in order to be certain; thus, we consider the specimens CFZ-MTZ540, 551, and 583 as cf. Bjuvia sp.

Thus far, there are only three species of this genus, all located in the Triassic of Europe. Bjuvia simplex Florin is characterized by having large leaves of up to 1 m in length and a venation density of 12-14 veins per cm; the venation can dichotomize at the base of the veins. Even though the size of the specimen studied here is incomplete, the venation density completely differs from that observed in B. simplex . The same occurs with the species B. dolomitica Wachtler et Van Konijnenburg-van Cittert, which only has 14-18 veins per centimeter, as well as a larger leaf width and a thicker rachis with a constant width. Regarding the third species, B. thalensis Kustatscher et Van Konijnenburg-van Cittert, though it has a size relatively similar to that of the specimen from Puebla, it also differs in the venation density, as well as in the width of the rachis ( Table 2 ).

In the case of the epidermal characters of the genus, the three reported species exhibit haplocheilic stomata, amphistomatic leaves, rectangular or square epidermal cells, and stomata generally in irregular rows with subsidiary cells and, in some cases, with papillae. The specimen from Puebla is similar to Bjuvia simplex in the shape of the abaxial epidermal cells, the size of the stomatal aperture, number of subsidiary cells and the presence of trichomes ( Barbacka, 2001). With B. dolomitica it shares the characters of the adaxial cuticle, since both have rectangular to irregular epidermal cells with straight to slightly crenulated walls (Wachtler and Van Konijnenburg-van Cittert, 2000). Finally, with B. thalensis it shares the presence of papillae in the stomatal apparatus ( Kustatscher and Van Konijnenburg-van Cittert, 2010).

Figures

FIGURE 3. Specimens of cf. Bjuvia sp. A) Largest specimen, CFZ-MTZ540. B) Specimen CFZ-MTZ583, in which a reduction in width toward the edges of the lamina can be observed. C) Close-up of specimen CFZ-MTZ540, in which the type of attachment of the lamina can be observed. D) Parallel venation observed in specimen CFZ-MTZ540. E) Adaxial cuticle extracted from specimen CFZ-MTZ583, with undulating epidermal walls. F) Abaxial cuticle extracted from specimen CFZ-MTZ540, in which straight epidermal cells can be observed. G and J) Stomata in the abaxial part of the cuticle of specimen CFZ-MTZ540, black arrows indicate papillae over stomatal opening and white arrows indicate subsidiary cells. H) Stomatal arrangement observed in the abaxial cuticle. I) Close-up of the adaxial cuticle where a simple trichome is observed, arrow indicates simple trichome. Abbreviations: m, leaf margin; r, rachis. Scale. A 5 cm, B and C 1 cm, D 0.5 cm, E, F and H 100µ, G 10 µ, I-J 50µ.