76 



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



B 



elliptical specimens of T. detriti and bears longitudinal ridges along 

 the leaf surface. The ordinary epidermal cells are, however, much 

 more elongate than those of T. detriti. Torreya nicanica Krassilov 

 (1967) from South Primorya differs considerably in having a short 

 petiole and stomata which are arranged in rows. 



Several other Mesozoic species with Torreya-\\V.Q leaves have 

 been described. Torreya gracilis Florin emend. Harris (1979) from 

 the Middle Jurassic of Yorkshire is of a similar size to T. detriti, but 

 differs in having a short flat petiole, a flat leaf surface, much more 

 elongate ordinary epidermal cells and a midrib marked by broader, 

 rather than narrower, cells on the upper cuticle. Torreya valida Florin 

 (1958) from the Middle Jurassic of Yorkshire has more elongate 

 ordinary epidermal cells and much broader stomatal grooves than 

 those of T. detriti. Torreya moelleri Florin (1958), from the Middle 

 Jurassic of Bornholm, Denmark, has a much longer leaf and the 

 stomata, which have fewer subsidiary cells, are arranged in rows. 

 Torreya longifolia Gomolitzky (1964) from the Jurassic of central 

 Asia has larger leaves with more elongate ordinary epidermal cells 

 and stomata with fewer subsidiary cells. Torreyites carolinianus 

 (Berry) Seward (1919), from the Middle Cretaceous of North Caro- 

 lina, is of a similar size to T detriti but the description by Berry 

 (1908) shows that the leaves taper much more gradually towards the 

 apex and that the stomata tend towards transverse rather than longi- 

 tudinal orientation. 



PALAEOECOLOGY 



Fig. 36 A-N Torreyites detriti sp. nov. Al! dispersed leaves from Wessex 

 Formation, Isle of Wight showing variety of shape and positions of 

 stomatal grooves. A-N, V.646 15-64628, all x 5: A-I, leaves with apex 

 more or less intact; J-N, leaves with twisted bases. 



be obtained by bulk maceration of debris material from the Lower 

 Cretaceous beds near where the original is probably from. 



It is possible that the small elliptical leaves represent juvenile 

 leaves, but leaf heteromorphism is not seen in modem Torreya and 

 there is far too little evidence to draw any conclusion about whether 

 this is the case in T. detriti. 



Comparison. Torreyites detriti is the only species of this genus to 

 be recognised within the English Wealden. Fig. 38A, B shows the 

 resemblance of T. detriti to the living species Torreya californica 

 Torrey which also has highly papillate stomatal grooves (Fig. 38C). 

 The leaves of T californica are, however, often four times the size of 

 the largest leaf of Torreyites detriti discovered so far. 



All the species resembling T detriti are refened to the genus 

 Torreya, none of them on the basis of anything other than gross 

 morphology and cuticle of leaves. Three of these are known from the 

 Lower Cretaceous. Torreya arctica Bose & Manum (1990) from 

 Spitsbergen is of a similar size to T. detriti but has stomata with fewer 

 subsidiary cells confined to stomatal bands which are not sunken and 

 which lack highly papillate margins. Torreya bureica Krassilov 

 (1973) from the Bureja Basin is of a similar size and shape to the 



The species described here, with the exception off! linkii. have been 

 found exclusively within debris beds and in a more or less fragmen- 

 tary state, suggesting that they may have been transported a fair 

 distance from their natural habitat, presumably on higher ground. 

 The addition of the species described here to the Wealden floral list 

 indicates that upland ecology, particularly that of areas draining into 

 the Wessex Basin, may have been more complex than previously 

 understood. Whilst dense forests of the cheirolepidiaceous conifer 

 Pseudofrenelopsis parceramosa undoubtedly dominated large areas 

 of higher ground (Watson & Alvin 1996: 23), there is growing 

 evidence of mixed communities of ginkgoes, czekanowskialeans 

 and needle-leaved conifers. 



The wild origins and ecology of Ginkgo biloba, the single extant 

 member of the Ginkgoales, are poorly known. It has been widely 

 cultivated in China and Japan for centuries and is known to be native 

 to Eastern China, where it might still occur as small populations in 

 mixed conifer-broadleaf forests in remote mountain valleys (Page 

 1990a). Ginkgo prevailed in moist and moderately warm conditions 

 during the Cenozoic (Uemura 1997), and its tendency for mesic 

 habitats may well have evolved earlier. Vakhrameev ( 1 99 1 ) certainly 

 regarded the Ginkgoales as a mesophilic group, attributing their 

 sharp reduction in the European province of the Late Jurassic to 

 increased aridity. 



Little is known about the ecology of the Czekanowskiales but a 

 wet and warm climate is thought to have been favourable for 

 Czekanowskia (Samylina & Kiritchkova 1993: 282), and both 

 Czekanowskia and Phoenicopsis are important within the humid, 

 moderately warm and seasonal conditions of the Early Cretaceous 

 Siberian-Canadian region (Vakhrameev 1991). The apparent disap- 

 pearance of the Czekanowskiales from the Euro-Sinian region was 

 noted by Vakhrameev (1 991: 127) as one of the most striking 

 differences between the two regions during the Early Cretaceous. 

 However, the discovery of Czekanowskia anguae and Phoenicopsis 

 rincewindii in the English Wealden provides evidence which suggests 



