Observations on Eristophyton Zalessky, Lyginorachis waltonii Calder, and Cladoxylon edromense sp. nov. from the Lower Carboniferous Cementstone Group of Scotland

ABSTRACT

Fifteen specimens of Eristophytonstems from the Lower Carboniferous Cementstone Group of Berwickshire and East Lothian have been examined. Three possess medullary rays comparable to E. waltoniiLacey, the others have rays like E. beinertianum(Göpp.) Zalessky. In one specimen assigned to E. waltoniia leaf-trace subdivides outside the secondary xylem to form an arc of six separate bundles. Another stem of E. waltoniihas attached closely spaced petiole bases one of which is clearly identifiable as Lyginorachiswith six vascular bundles arranged in an arc. Stems of Eristophytonfrom five localities occur associated with petioles or rachises possessing a U-shaped vascular bundle with abaxial ridges like L. waltoniiCalder. As these may occur mixed with rachises agreeing with L. browniiCalder the latter is regarded as synonymous. Detached petioles found associated with E. beinertianummay possess four or six basal bundles. The evidence suggests that the U-shaped petiolar bundle passes down into four then six basal bundles and such petioles are associated with both E. waltoniiand E. beinertianum. Calder (1935, pl. 1, fig. 2) showed dichotomy in the petiole bundle.

In addition different rachises are known possessing a more massive U-shaped bundle but lacking sclerotic nests and sparganum outer cortex. These are assigned to Cladoxylon edromensesp. nov. Cortical nests occur in both E. waltoniiand L. waltoniiand may be compared with the sclerotic plates in the compressions of Diplotmema dissectumBrongn. and D. patentissimumEtt.. The evidence supports the view that Eristophytonis a pteridosperm with bifurcate fronds known as L. waltoniiCalder when petrified and comparable to Diplotmemawhen compressed.