32 



venient to study the Ginkgoales and Czekanowskiales together, 

 particularly when dealing with fragmentary leaves and cuticles 

 which can be difficult to distinguish and it would not be prudent to 

 study one without the other. 



In tribute to the author Terry Pratchett OBE, all the new fossil 

 plant species diagnosed and described in this paper are named for 

 fictional characters who appear in his series of Discworld novels. 



SYSTEMATIC DESCRIPTIONS 



GYMNOSPERMAE 

 Order CZEKANOWSKIALES 



Harris ( 1 935 ) first attributed the cupulate fructification Leptostrobiis 

 Heer to the leaf genus Czekanowskia Heer when studying the 

 Scoresby Sound flora from East Greenland, though at that fime the 

 precise nature of the reproductive structure was unclear. When later 

 studying the Middle Jurassic flora of Yorkshire Harris (1951) was 

 able to elucidate the exact structure of the Leptostrobiis seed cap- 

 sules and repeated the attribution (see also Harris & Miller 1974). 

 The order Czekanowskiales was subsequently named by Pant ( 1 959) 

 in order to accommodate these associated organs and isolate them 

 from the Ginkgoales. Since then Russian authors (e.g. Krassilov 

 1972) have confirmed the strong evidence, with the repeated asso- 

 ciation of Leptostrobiis not only with Czekanowskia leaves but also 

 with those of Phoenicopsis. Otherwise there has been little further 

 evidence and other aspects of these plants including the pollen 

 organs remain obscure. Thus the order remains poorly characterised 

 and there is no evidence at present to support a further subdivision of 

 the order into families. 



The foliage leaves attributed to the Czekanowskiales are all borne 

 in bundles on short caducous shoots which are covered with small 

 scale leaves. The three main leaf-genera included in the order are 

 Solenites Lindley & Hutton, Czekanowskia Heer and Phoenicopsis 

 Heer. These three genera also share the possession of a single vein 

 entering at the base of the foliage leaf but can easily be distinguished 

 according to gross morphological features. Czekanowskia Heer and 

 Phoenicopsis Heer which are now known to be represented in the 

 English Wealden flora can be separated thus: 



Foliage leaves linear, divided, each with one or two veins. 



Czekanowskia Heer 

 Foliage leaves narrowly wedge-shaped with numerous veins. 



Phoenicopsis Heer 



Other czekanowskialean leaf genera are discussed at length by 

 Harris and Miller (1974: 79) and this remains an extremely useful 

 account notwithstanding other treatments by Krassilov (1972) and 

 Samylina & Kiritchkova ( 1 99 1 . 1 993 ). Samylina ( 1 972 ) established 

 sub-genera within Phoenicopsis and later (Samylina & Kiritchkova 

 1 993) within Czekanowskia. based on cuticle characters. Despite the 

 difficulties of separating the leaves of the Ginkgoales and 

 Czekanowskiales the cuticle of the latter can be quite distinctive, 

 with characteristic features which include: ordinary epidermal cells 

 arranged in longitudinal files, frequently with oblique or pointed end 

 walls; longitudinal arrangement of haplocheilic stomata; cutinization 

 of inner periclinal walls of isolated cells in the epidermis, particu- 

 larly the subsidiary cells. This is further discussed and illustrated 

 below. 



J. WATSON, S.J. LYDON & N.A. HARRISON 

 Genus CZEKANOWSKIA Heer 



1876 Czekanowskia Heer: 65. 



1936a Czekanowskia Heer; Florin: 128. 



1972 Czekanowskia Heer: Krassilov: 12. 



1974 Czekanowskia Heer; Harris & Miller: 92. 



1991 Czekanowskia Heer; Samylina & Kiritchkova: 30. 



1993 Czekanowskia Heer; Samylina & Kiritchkova: 273. 



Type species. Czekanowskia setacea Heer 1876: 68; pis 5, 6 

 (cudcle figured by Florin 1936a; text-fig.l2). 



Diagnosis, [emended by Harris & Miller, 1974: 92] Caducous 

 short shoot covered with persistent scale leaves and bearing bundle 

 of foliage leaves. Foliage leaf, as a whole, wedge-shaped, dividing 

 by dichotomies into number of filiform segments; segments ending 

 in acute apex. Leaf substance thick, probably oval in section. Vein 

 single at leaf base, forking well below lamina dichotomy: apex with 

 single vein. Resin bodies absent. 



Cuticle well developed, similar on the two sides, amphistomatic; 

 stomata occurring mainly in more or less short longitudinal files. 

 Stomatal files almost evenly distributed over whole epidermis (in- 

 cluding veins and at leaf margins). Stomata longitudinally orientated, 

 haplocheilic, guard cells sunk in pit formed by subsidiary cells, two 

 of which are usually terminal. Pit commonly reduced by rim or 

 papillate pads of subsidiary cells. Encircling cells occasional. 



Discussion. Cuticles from the two sides of Czekanowskia foliage 

 leaves are not easily designated 'upper' and 'lower' and indeed these 

 terms are less appropriate for leaves which are borne in bundles. The 

 wider leaves of Phoenicopsis sometimes exhibit a dorsi-ventral 

 differentiation and the cuticles are then designated 'thicker' and 

 'thinner', possibly upper and lower respectively. The narrow one- or 

 two-veined leaves of Czekanowskia exhibit no such differentiation 

 and the reason for this might be apparent in some Jurassic 

 uncompressed Czekanowskia leaves which have been described as 

 round in transverse secfion by Hill (C.R. Hill, pers. comm. 1987). In 

 such leaves, the description of cuticle from each 'leaf-surface" in the 

 compression fossil, loses its value. Nevertheless, two distinct sur- 

 faces can be detected on the grounds of stomatal density. Samylina 

 and Kiritchkova (1991, 1993) have described the leaf cross-section 

 as trapezium-like or rectangular but this is not confirmed in York- 

 shire Jurassic material or from the Wealden specimens. 



Three subgenera within the genus Czekanowskia Heer have been 

 recognised by Samylina & Kiritchkova (1991, 1993). These are: 

 subgenus Czekanowskia with amphistomatic leaves, stomata in files; 

 subgenus Harrisella with amphistomatic leaves, stomata in bands at 

 leaston lower epidermis; subgenus Vac/jraweev/fl withhypostomatic 

 leaves, stomata in files or bands. Seventy four species of 

 Czekanowskia. from more than 160 Mesozoic localities in the North- 

 ern Hemisphere, divided between these three subgenera are listed by 

 Samylina & Kiritchkova ( 1 99 1 ). All of the Lower Cretaceous occur- 

 rences are geographically extremely remote from the Wealden. 



Czekanowskia anguae sp. nov. 



Figs 1-3 



Diagnosis, [based on leaf fragments only] Leaf 1-2 mm wide. 

 more than 6 mm long, tapering to mucronate apex [veins unknown]. 

 Stomata present on both leaf surfaces, cuticle 4 pm thick. Stomata 

 always longitudinally orientated, arranged in short or long longitudi- 

 nal rows. Stomatal apparatus averaging 59 (37-100) jam long and 47 

 (24-101) |jm wide. Guard cells with wide, thickly cutinized semi- 

 circular dorsal plates and square-ended polar thickenings, sunken 

 beneath ring of 2 polar plus 2 to 6 lateral subsidiary cells. Raised 

 rectangular rim to stomatal pit, partially exposing guard cells and 



