REVISION OF THE ENGLISH WEALDEN FLORA 



63 



is thinly ciitinized beyond the dorsal plates, resulting in fully devel- 

 oped T-pieces or polar appendages (Figs 24G, I; 25E, F). The ventral 

 wall of the guard cells is also frequently represented in the fossil as 

 a thin sheet of cuticle (Fig. 241). 



Discussion and comparison. PseudotorelUa vimesiana sp. nov. 

 was first recorded as an unnamed leaf sample in the Wealden leaf 

 coal of Duingen, North West Germany (Miigdefrau & Rudolf 1969: 

 297), where it occurs alongside the larger and much more numerous 

 leaves oi PseudotorelUa linkii (Romer) Watson & Harrison ( 1998). 

 It is formally diagnosed and named here for the first time. 



P. vimesiana is readily distinguished, by the small size of its 

 leaves, from the two other species of PseudotorelUa which are 

 known to occur in the German Wealden leaf coal. P. linkii and a new 

 undescribed species (Watson et al. in preparation). The leaves of P. 

 vimesiana never exceed 1 .7 mm in width and the stomata have guard 

 cells generally less than 60 pm long beneath oval, crater-like pits. 

 Nevertheless, several features suggest a close affinity with 

 PseudotorelUa linkii: the arrangement of stomata in two or three 

 bands in the leaf base merging distally into one band: the thick 

 cutinization of the anticlinal walls around the leaf base; the presence 

 of resin canals. It is mainly this similarity with P. linkii which leads 

 us to assign this species to PseudotorelUa, since no evidence of veins 

 has been found. It should be noted however that isolated distal leaf 

 fragments with a single median stomatal band and resin canals 

 present certain difficulties of generic assignment and. for example, 

 those in Fig. 25A, B could have been readily attributed to 

 Sciadopityoides without evidence from other specimens. The prob- 

 lems associated with generic usage for this group of leaves is 

 discussed below in the account of Sciadopityoides. 



Form-genus SCIADOPITYOIDES Sveshnikova 



1981 Sciadopityoides Sye.&hmk.o\n: Mil. 



1987 Sciadopityoides S,\e.s\\mko\3L\Ma.num: 159. 



1990 Sciadopityoides Sveshnikova; Bose & Manum: 21. 



Type species. Sciadopithys uralensis Dorofeev & Sveshnikova 

 1959: 1277; pl.2, figs. 1-7. 



Diagnosis, [based on Sveshnikova 1981 (in Russian) with slight 

 emendments] Leaves linear, lanceolate or more broadly elliptical. 

 Apex obtuse or acuminate. Cells of the upper epidermis, and of the 

 lower in lateral areas outside median stomatal zone, seriately arranged, 

 without papillae. Lower surface of leaf with a median stomatal zone, 

 which may or may not be in a groove. Epidermal cells of stomatal 

 zone less seriately arranged than in rest of leaf. Stomata monocyclic, 

 longitudinally or transversely orientated or with no preferred orien- 

 tation. Subsidiary cells 4 to 6, but may be up to 9. Subsidiary and 

 non-stomatal cells inside groove with or without papillae. 



Discussion. Sveshnikova (1981) erected the form-genus 

 Sciadopityoides to accommodate all Mesozoic conifer-like leaves 

 which resemble the living Sciadopitys inasmuch as they have a 

 median stomatal band, but with no natural affinities implied and in 

 practice evidence of familial position is usually completely lacking. 

 Thus Sciadopityoides sensu Sveshnikova became a useful form- 

 genus for leaves of this type with stomata confined to a band along 

 the middle of the lower surface (Hall 1987; Manum 1987) and of 

 probable conifer affinity, though sometimes with characters reminis- 

 cent of the Ginkgoales (see comments by Watson & Harrison 1998). 

 This is the sense in which Sciadopityoides is used here. However, 

 several other genera have subsequently been erected (Reymanowna 

 1985; Bose & Manum 1990, 1991) which overlapped with 



Sciadopityoides and changed its usage. In particular Bose & Manum 

 (1990) undertook an extensive study and reassessment of 

 ' Sciadopitys-hkc leaves from the Mesozoic of northern Europe and 

 established a new conifer family, the Miroviaceae, containing sev- 

 eral new leaf genera, including Mirovia Reymanowna (1985) but 

 without evidence from reproductive structures. It is interesting to 

 note that Reymanowna (1985) considered Mirovia to be close to 

 PseudotorelUa and probably ginkgoalean. 



In the genera assigned to the Miroviaceae Bose & Manum ( 1 990, 

 1991) and Manum et al. (2000) have given considerable weight to 

 the presence of a median groove or line of differentiation on the 

 upper epidermis which they take as circumstantial evidence for a 

 double vein such as occurs in the leaves of Sciadopitys verticillata, 

 a unique feature amongst living conifers. However, PseudotorelUa 

 linkii (Romer) often has such a midline feature on leaves (Fig. 22D; 

 see also Watson & Harrison 1998) with numerous dichotomising 

 veins. Furthermore, the leaves of Abies and similar modem conifers 

 often display such a midline groove over their single vein (Watson & 

 Harrison 1998, figs ID, 2A-D). It thus seems unwise to regard the 

 presence of such a feature in fossil leaves as in any way indicative of 

 leaf venation. 



It has become clear that there are numerous Mesozoic species of 

 the Sciadopityoides and PsettdotoreUia type, variously referred to 

 the Coniferales or Ginkgoales, with a distinctive suite of characters 

 in common. Many of them are known to be heterophyllous with both 

 needle-like and more or less elliptical leaves; some are associated 

 with and/or attributed to shoots of the Sulcatocladus type. The 

 shared features of these plants might well indicate a family relation- 

 ship, almost certainly coniferous, but conclusive evidence from 

 reproductive structures is entirely lacking. Therefore in the absence 

 of any positive evidence of this kind we propose to include Wealden 

 leaves with a median stomatal band in the form-genus Sciadopityoides 

 sensu Sveshnikova (1981). 



Sciadopityoides greeboana sp. nov. 



Figs 26-30 



1976 27 GINK GkA Oldham (Code used in place of Linnean 

 binomial): 460; pl.70, figs 3-6; pi. 71, figs 1, 3, 5. 



Diagnosis. Leaf linear, up to at least 9 mm long, 0.5-1.5 mm 

 wide. Apex acute, frequently missing. Base slightly constricted. 2-3 

 resin canals present in some leaves, longitudinally aligned, 

 unbranched. 



Upper cuticle 5-20 |am thick, stomata usually absent, very 

 occasionally one or two stomata present on whole leat. Epidermal 

 cells arranged in longitudinal files; rectangular or square; generally 

 35-1 1 5 |im long x 1 5-40 pm wide; along midline narrower and more 

 elongate; near leaf base, shorter, as little as 5 pm long. Longitudinal 

 bars between pairs of cells common. Anticlinal walls generally 5-10 

 pm thick, straight or slightly sinuous; near leaf base, 1 0-20 |am wide, 

 strongly sinuous. Outer periclinal walls 5-17 pm thick, of uniform 

 thickness or, more commonly, with a solid, median, longitudinal 

 ridge over a file of cells, occasionally restricted to one cell, rarely 

 longitudinal rows of hollow papillae take the place of ridges; outside 

 surface finely pitted; inside surface finely granular. Inner periclinal 

 walls 0.5-1.0 pm thick. Hypodermis usually present. Hypodermal 

 cells approximately square. 23-46 pm long x 27-46 pm wide; 

 arranged in longitudinal files; anticlinal walls frequently sinuous. 



Lower cuticle with stomata confined to a median band, sometimes 

 in a groove. In lateral, stomatal-free zones, cuticle 5-20 pm thick; 

 ep'dermal cells similar shape, size and arrangement to those of upper 

 surface; hypodermis present. Stomatal band 1/3-2/3 of total leaf 

 width; tapering to a point just below leaf apex; cuticle 3-8 pm thick. 

 Ordinary epidermal cells in stomatal band, arranged in longitudinal 



