Czekanowskia sp.

León, María Patricia Velasco de, Martínez, Erika Lourdes Ortiz, Barragan, Miguel Angel Flores, Madrid, Diana Silvia Guzmán & Martinez, Pedro Christian Martínez, 2024, New records of Bennettitales and associated flora from the Jurassic of the Cualac Formation, Mexico, Palaeontologia Electronica (a 14) 27 (1), pp. 1-19 : 14

Czekanowskia sp.

Figure 5 H-I

Material examined. CFZCr105, Cr135 Description. Incomplete laciniate leaf impressions, stiff and firm in appearance; bundle of up to nine laciniae united at base, without short outgrowths, largest leaves up to 71.8 mm long and

0.61-2 mm wide, at base the specimen is dichotomous up to twice ( Figure 5H ). Each lacinia bears a distinct median vein, the apex is unknown. The laciniae diverge at angles of 15°-22°.

Discussion. Leaves of the Czekanowskiales are borne on short shoots, are deciduous and are surrounded by squamiform leaves; the laminae are elongate, simple, or dichotomously segmented, with a single vein at the base of the leaf, usually forked several times, not anastomosing, so that at least one vein remains per leaf segment resulting. There are three genera; the first, Solenites Lindley and Hutton is characterized by a leaf without segmentation; Phoenicopsis Heer with leaves that are narrow wedge-shaped with numerous veins and Czekanowskia Heer with linear, segmented leaves 1 mm wide and a vein ( Harris and Miller 1974; Watson et al., 2001). The material studied here has a single vein and leaves with a width of 1.2 mm and bifurcation is therefore assigned to Czekanowskia .

Czekanowskia is distributed in the Northern Hemisphere from the upper Triassic to the Cretaceous ( Taylor et al., 2009). Harris and Miller (1974) recorded four species in Yorkshire, UK: C. furcula Harris and Miller , 1 mm wide over most of the leaf, tapering towards the apex and over 120 mm long; it also has eight-leaved bundles; the latter character distinguishes it from the Oaxacan species as seen in the specimen, CFZCr 105-135, Figure 5 HI. Czekanowskia thomasi Harris and Miller has few, delicate, unevenly sized leaves; its foliage with leaf bundles of seven to eight leaves, and up to 80 mm in length. Most leaf segments fork once and are mostly 0-5 mm wide. The fossil studied here does not have any of the diagnostic characters of C. thomasi the third species, Czekanowskia blacki Harris and Miller , has twice forked leaves with unequal size and about seven leaves per bundle, over 140 mm in length; again, the specimens from Mexico are characterized by leaves of constant size and are therefore not assignable to this species. Finally, Czekanowskia microphylla Harris and Miller has leaves forked three times, in bundles of five leaves. Both of these characters differentiate it from the Cualac Formation specimen. Therefore, the material presented here differs from that of the UK. Other species have been proposed from Russia, many of them from the Cretaceous, and others from the Wealden flora by Watson et al. (2001) where cuticle is used as the main character. As no cuticle could be obtained so far from our specimens the assignment to any species is impossible, and we leave the record at genus level only.

Figures

FIGURE 5. Leaves of Mexiglossa and Czekanowskia. A-B - whole leaves of Mexiglossa varia, note that the midvein cells; C-E- F-G light microscopic images, rectangular epidermal cells of Mexiglossa with straight walls; D - electron microscopy image, thick walls of epidermal cells; F - arrows indicate two stomata; G - trichomes present on leaves of Mexigossa varia; H - linear leaves of the genus Czekanowskia, the arrows indicate the middle vein and the fork of the leaf; I - specimen CFZcr105 shows base of bundle of laciniae, the arrow indicates a bifurcation. Scale in A 3 cm; B 3 cm; C 10 μm; D 50 μm; E 15 μm; F 15 μm; G 2.5 μm; H 1 mm; I 5 mm.