XVI International Botanical Congess
This contribution reports new Silurian-Lower Devonian land-plant assemblages in Bolivia and Argentina. In the Ludlow-Pridoli of Southern Bolivia we have found Cooksonia, the earliest pteridophyte-like plant recorded in Laurassia, diverse rhyniophytoids and further more enigmatic fossils. There is no evidence for Baragwanathia in Bolivia although it is recorded in Australia during this time interval. Such differences emphasise the existence of at least two phytogeographic processes in Gondwana at this time. In the Lower Devonian of Argentina plants are recorded in the Villavicencio and Talacasto Formations, relatively well and independently dated as Lochkovian and in the younger but less securely dated Punta Negra Formation. The latter contains abundant debris, including some sporangia, that are impossible to classify. The Lochkovian plants are more complete and include specimens with terminal sporangia and enations. However, although at approximately same organisational grade as coeval plants elsewhere, none can be assigned to existing taxa, suggesting that this part of Gondwana had a distinct flora in early Devonian times, which is possibly related to its isolation at high latitudes.