38 



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



Fig. 5 A-F Phoenicopsis rincewindii sp. nov. A, B, stomatal distribution and orientation across width of leaf. Same leaf margin on right of Fig. A and left 

 of Fig. B. A, presumed lower (thinner) cuticle, B, presumed upper (thicker) cuticle, both V.64526, x 50; C, stomatal pair from the lower cuticle, V.64526, 

 X 400; D-F, stylised stoma based on observations in the SEM, approximately x 1000; D, viewed from inside of cuticle; E, transverse- vertical section 

 along line a-a; F, longitudinal-vertical section along line b-b; g -guard cell; s - subsidiary cell. 



and 6C. In the light microscope, the subsidiary cells appear darker 

 than those of the general epidermis (Figs 4F, 5C, 6A, C) because of 

 the greater thickness of their surface walls. In many Czekanowskiales 

 this appearance is caused by the cutinization of the inner periclinal 

 walls, but the SEM has, as yet, afforded no evidence of inner 

 periclinal cutinization on the subsidiary cells off. rincewindii (Fig. 

 4G, H). The typical arrangement of the subsidiary cells in this 

 species, a single polar subsidiary cell at each end of the stomatal pit 

 and one or two lateral subsidiary cells on each side, is shown in Figs 

 4G, 5C, D. The thickened inner anticlinal walls of the subsidiary 

 cells frequently form flat papillae on the lateral cells protruding over 

 the stomatal pit (Figs 4F, I; 5C; 6C, D ). The characteristic axe-head 

 shaped outline of the guard cell-dorsal plates is shown in Figs 4H and 

 5D 



Discussion. P. rincewindii sp. nov. exhibits the following 

 czekanowskialean features: linear leaves; stomata in files; subsidi- 

 ary cells with thicker periclinal walls than other epidermal cells. It is 

 assigned to the genus Phoenicopsis rather than Czekanowskia because 



of the numerous parallel veins, and to the sub-genus Culgoweria 

 because the stomata are on both leaf surfaces and arranged in files 

 (see generic discussion above). 



Comparison. The general arrangement of the stomata and the 

 common occurrence of stomatal pairs in P. rincewindii is reminis- 

 cent of Phoenicopsis steenstrupii Seward (1926) from the Lower 

 Cretaceous of western Greenland, which is also attributable to the 

 subgenus Culgoweria. However, material of P. steenstrupii was 

 reinvestigated (Hall 1987) and the two species were found to be 

 easily distinguished by differences in stomatal densities on both 

 surfaces, stomatal orientation, nature of the anticlinal cell walls and 

 length of ordinary epidermal cells. 



The extremely limited number of specimens of P. rincewindii 

 prevents useful comparison of gross morphology with the many 

 other species of Phoenicopsis described in particular by Samylina 

 (1972), Sun (1987) and Zhou & Zhang (1998), and this must await 

 further discoveries in the debris bed material. 



