REVISION OF THE ENGLISH WEALDEN FLORA 



variety of leaf size and shape. The leaf outlines fall into two groups, 

 those which are needle-like (Figs 22A, C, D; 23D, E. F, G) and those 

 which aie more or less elliptical (Figs 22B; 23A-C). The former are 

 largely the leaves originally described as the conifer Abietites linkii 

 (Romer) and the latter more or less represent the material which was 

 described by Watson (1969) as a new species of Pseuclotorellia, but 

 which also included needle-like leaves known to have two or more 

 veins. Wide, elliptical leaves are well-known from the German 

 Wealden but Watson & Hanison's (1998) identification and interpre- 

 tation of the German specimens has been rejected by Manum er al. 

 (2000), largely on the basis of the needle leaves and the elliptical 

 leaves occurring separately and at different stratigraphic horizons. 

 However, since Manum et al. (2000) have refrained from presenting 

 cuticle evidence (a cornerstone of Mesozoic palaeobotany) in sup- 

 port of this rejection, we are unable to accept their alternative thesis 

 at present. The salient features of the recombined species P. linkii 

 (Romer), based on English and Gennan material, are summarised 

 below. 



The needle leaves are parallel-sided (or sub-parallel ) with a tapering 

 or rounded apex (Fig. 22 A, C, D) and sometimes a twisted base (Figs 

 22A 4th from right; 23D, E). The known width of needles is 1 to 3 

 mm but relatively few whole needle leaves have been recovered (Fig. 

 22A far left, D). The known length to width ratio in needles is 8: 1 in 

 the shortest (Fig. 22A sixth from right) and just over 20: 1 in the 

 longest (Fig. 22A extreme left). The veins in long needles have been 

 repeatedly demonstrated as at least two in number but some needle 

 leaves as narrow as 1.4 mm certainly have up to four (Fig. 22E). 



The elliptical leaves show a wide variety of shape and size (Figs 

 22B; 23 A-C) with a known range of 4 to 8 mm wide and 1 to 40 mm 

 long, plus one exceptionally large leaf from Germany which is 15 

 mm wide and 60 mm long (Watson & Harrison 1998, tigs 4A, B; 

 6M). The shape of the broader leaves of P. linkii varies from sub- 

 parallel (Fig. 22B left) through well-formed ellipses (Fig.23A, B) 

 with symmetrical distal and proximal halves, to obovate with a 

 broad, blunt apex (Fig. 22B second from left). 



Watson & Harrison (1998) have discussed and speculated about 

 the significance of the heterophylly and the probability that the two 

 leaf forms represent juvenile and adult foliage of one tree species. 

 They suggested that the wide leaves are more likely to be juvenile 

 and the needle leaves adult. However, the evidence remains slim 

 despite the huge array of P. linkii leaves available. Watson & 

 Harrison's (1998: 247) reasons hinge upon the wider leaves (which 

 are far fewer in number in the leaf deposits) having great variation in 

 shape and size, which could indicate the unsettled morphology of 

 juvenile foliage and might also reflect a probable wide ancestral 

 form. Some modern conifers such as Junipents have large juvenile 

 and small adult foliage. The needles off! linkii. which occur in vastly 

 larger numbers than wide leaves, are more consistent in shape and 

 size, suggesting the stable moiphology of leaves in the main part of 

 the plant. Smaller leaves are of course a more advanced character in 

 conifers. 



The extreme tip of the leaf, which was possibly scarious, is almost 

 always missing (Fig. 23A, B, F, G) but a rare example of a leaf with 

 an intact, pointed tip is shown in Fig. 22G. The bases of both the 

 needles and the wider leaves sometimes show twisting and/or trans- 

 verse wrinkling, thought to be related to post-mortem shrinkage of a 

 triangular leaf-base with the apex and two sides disposed adaxially, 

 and the base of the triangle abaxially. Some well-preserved P. linkii 

 leaves reveal this triangular cross-section, with the apex in the centre 

 of the upper surface and a flat lower surface (see Watson & Harrison 

 1998, fig. 9F, G) and despite not having been found connected to a 

 shoot, there seems to us little doubt that the triangular leaf-bases 

 were attached to the shoots of Sulcatocladus robustus Watson & 



59 



Harrison ( 1 998) in life. The two are repeatedly associated and their 

 remarkabl) similar cuticles possess the same unusual, distinctive 

 characters. 



The cuticle of P. linkii is extremely thick ( 1 5-50 pm) on both leaf 

 surfaces with stomata restricted to the abaxial surface, unrelated in 

 arrangement to the position and number of veins which vary from 2 

 to at least 12, according to the width of leaf The leaf base shows the 

 entry of two veins which give rise to branches on their inner sides 

 (Fig, 23A-C) in the lower part of the leaf Distally beyond the 

 branching the veins run parallel to one another (Figs 22C, F: 23 A-D ) 

 then converge towards the apex. The veins are more resistant to 

 maceration than the mesophyll and can easily be seen as black 

 strands if maceration is halted before completion (Figs 22E; 23 A- 

 C). Brittle, amber-coloured strands of resin, which fluoresce under 

 ultraviolet light, appear to be infills of resin canals running unbranched 

 along the full length of the leaf, each strand lying directly beneath a 

 stomatal band (Fig. 23F, G). 



Fig. 22L, M shows the upper cuticle devoid of stomata, with 

 square to rectangular epidermal cells arranged in longitudinal files, 

 and the characteristic pairs of cells which underwent late division 

 (Fig. 22M). The upper cuticle is typically smooth on the outer 

 surface but commonly has hemispherical cuticular thickenings or 

 pustules (Fig. 22L) on the inside surface of the outer periclinal walls, 

 particularly near the leaf base. 



Ordinary epidermal cells of the lower cuticle are similar in size to 

 those of the upper epidermis and are also arranged in longitudinal 

 files (Fig. 22H, I), though less strictly amongst the stomatal bands. 

 The outside surface of the lower epidermis is very variable, some- 

 times as smooth as in Fig. 22J, sometimes with weakly developed 

 cuticular ridges running along the length of a file of cells (see Watson 

 & Harrison 1 998, fig. 1 3B ) or with very strongly developed ridges as 

 in Fig. 22K. Fig. 221 shows the same distinctive pustules on the 

 inside of the ordinary epidermal cells as occur in the upper cuticle. 

 Stomata are absent from the extreme base of the leaf but 2 or 3 

 distinct stomatal bands (Fig. 23G) are initiated just above the base 

 (see Watson & Harrison 1998, fig. 8C), generally remaining distinct 

 until about half way up the leaf ( Figs 22H ), then merging distally into 

 a single broad band (Watson & Harrison 1998, fig. 8A) which 

 continues to the apex. Occasionally the stomata are arranged in one 

 broad longitudinal band, more often in the wide elliptical and 

 obovate leaves (Watson & Harrison 1998, fig. 1 IG) than in needle 

 leaves. The stomata are all longitudinally aligned and have a more or 

 less rectangular pit, usually overhung by subsidiary cell papillae 

 (Figs 22J, K), but are occasionally smooth-rimmed. Aborted sto- 

 mata, with single, undivided guard cell mother cells are a common 

 feature in leaves of P. linkii from all localities. Figs 22H, I. N show 

 the distinctive, thickly cutinized, dorsal plates of the guard-cells, 

 with their typical long, strongly cutinized polar appendages. 



Discussion. The revision of this species by Watson & Harrison 

 (1998) united three separate species from Lower Cretaceous floras 

 of England, Greenland and Germany. The evidence for this comes 

 largely from the cuticle, which is identical in all three floras, but also 

 from the discovery that the long-known German Wealden needles 

 attributed Xo Abietites linkii Romer (1839) did not possess a single- 

 veined 'midrib' as had long been supposed. The recognition in all the 

 leaves of parallel, dichotomising veins ending freely in the distal 

 margins, led to the newly combined species being assigned to the 

 genus Pseiidotorellia Florin and removed from the Ginkgoalcs with 

 temative reattribution to the Coniferales, supported by the associated 

 Sulcatocladus shoots. 



The leaves of P. linkii were almost certainly deciduous and Watson 

 & Harrison ( 1 998) have discussed the evidence for this. The presence 



