The earliest vascular land plants: continuing the search for proof

New collections from Bringewoodian strata (Silurian, Ludlow Series, Saetograptus leintwardinensis incipiens Zone) in Wales have yielded the oldest known specimens of the plant Cooksonia. From evidence at younger (Eř;éolí/Downton) horizons this genus is considered to be a vascular plant; although no tracheids have been isolated from the Bringewoodian specimens, on the basis of comparative morphology they are concluded to be the oldest recorded tracheophytes. The types of evidence relevant to the identification of vascular plants are briefly reviewed, and the relationships of the Welsh Cooksonia flora to other late Silurian floras are discussed. Confident stratigraphical dating is a prerequisite for any discussion of early plant evolution, emphasising the desirability of an integrated approach incorporating both geologial and palaeobotanical investigations. The dating of two published records of diverse Silurian floras, including lycopods, is questioned; recent dating of the Australian Baragwanathia flora as early Ludlow on the basis of graptolites is not supported by the shelly faunal evidence, which indicates a correlation within the Lower Devonian.