Article: The ultrastructure of spores of Cooksonia pertoni

The ultrastructure of spores isolated from sporangia of Cooksonia pertoni from Pridoli and Lochkovian rocks of the Welsh Borderland has been elucidated using both scanning and transmission electr microscopy. The Silurian material, attributable to C. pertoni subsp. synorispora, contains Synorispori vermcatus while the Devonian C. pertoni subsp. apiculispora yields either Streelispora newportensis Aneurospora sp. All three spore taxa show an exospore (= exine) composed of two layers, both of which extend into the murornate and verrucate sculpture in Synorisporites vermcatus, into the papillae and proximal folds of Streelispora newportensis, and into apertural folds (where observed) in all three taxa. In contrast, only the outer layer occurs in the apiculate sculpture of the Devonian spores. The homology of the layers is briefly discussed in relation to extant vascular cryptogams. Such ultrastructural observations compare favoural with published descriptions of the same taxa recorded from dispersed assemblages using light microscopy. Similar ultrastructure has already been recorded in cf. Ambitisporites isolated from Pridoli Cooksonia pertoni from Long Mountain, Shropshire, thus providing support for the hypothesis that, while the gross morphology and spore structure of C. pertoni remained unchanged from the Silurian into the Devonian, spore sculpture evolved from smooth to verrucate to apiculate.