Rhacopteris transitionis STUR , 1875

Rhacopteris transitionis STUR, 1875

Text-fig. 8a View Text-fig

1875 Rhacopteris transitionis STUR , p. 77, 86, pl. 8, figs 5–7. 1923 Rhacopteris transitionis STUR ; Kidston, p. 219, pl. 50,

fig. 1, pl. 53, fig. 1 (?pl. 51, fig. 4).

D e s c r i p t i o n. Once-pinnate frond with stout, finelystriate rachis up to 5 mm wide. Petiolate pinnules touching or very close, attached to rachis at 70–80°. Pinnules ca. 15 mm long, 7 mm wide in middle of frond, becoming gradually smaller in more distal and proximal positions. Pinnule shape asymmetrically rhomboidal, shallowly divided into up to seven lobes. Fine veins radiate from base with a single vein entering each pinnule lobe.

R e m a r k s. Although a rare species, Kidston (1923) documented some particularly well-preserved specimens from the Lower Limestone Formation. The systematic affinities of this species remain uncertain and Hübers et al. (2014) suggested that it might be an immature pteridosperm, by implication a lyginopteridalean. However, the very robust rachis and asymmetrical pinnules suggest that it is probably a Rhacopteris .

O c c u r r e n c e s. Rare in Lower Limestone Formation, notably from the Top Hosie Limestone (Limekilns),

Lanarkshire; and a record from an ironstone above the Top Hosie Limestone (lower Limestone Coal Formation).