Permian phytogeography in Gondwana

Phytogeographic patterns based on multivariate techniques (Multidimensional Scaling) are proposed for the Permian vegetation of Gondwana. This approach requires a data set with broad geographic coverage based on generic composition and with good time control. In general, strong phytogeographic differentiation can be observed throughout the Permian. In order to identify short term phytogeographic patterns, the Permian period was informally divided into five time slices. In the Permian Stage I (earliest Permian) the vegetation was strongly influenced by glacial conditions; a very impoverished vegetation is seen except in Patagonia and parts of South America. Four units were identified: Patagonia, Nothosouthamerica, Australia and Indo-Africa. By far, Patagonia was the most diverse and had the most favourable climatic conditions, perhaps as a result of palaeogeographic separation from western Gondwana. Nothosouthamerica, which included plant assemblages from NW Argentina and Brazil (perhaps as two subunits), is a mid-latitude area with glacial influence in the Brazilian sector. Indo-Africa had a much lower diversity occupying high latitudes, whereas Australia had the lowest diversity of all the vegetational regions in Stage I. The early Permian Stage II shows a more diversified and expanded plant cover. Vegetation of eastern and western Gondwana was differentiated; Patagonia and South America (including a Brazilian and NW Argentinean unit) had the richest plant assemblages, whereas Africa, Indo-Australia and Antarctica (as separate units) are less diverse probably due to late glacial influence. By the late early Permian (Stage III), Gondwana shows much more ameliorated climatic conditions basically due to drifting into more temperate latitudes, as well as increased moisture resulting in expansion of peat-forming areas. This is immediately reflected in the vegetation as shown by diversified plant assemblages, even in Antarctica. Nonetheless, a differentiation is again observed between eastern Gondwana (Patagonian and South American Units) and the western sector (Indo-Australian and Antarctic Units), whereas Africa would probably represent an ecotone. Beginning in the late Permian (Stage IV) there was a decrease in the number of plant assemblages and diversity, indicating a deterioration in climate resulting from generally drier conditions. Latitudinal differentiation can be observed, with Antarctica as a polar unit, Afro-Australia at high latitudes, whereas the South American-Indian and Patagonian Units are located in middle latitudes. Finally, in Permian Stage V (latest Permian) a South American Unit can be differentiated clearly from the rest (Africa and Indo-Australia); Antarctica is interpreted again as a discrete unit. In the Stage V time slice eastern Gondwana returns to more humid climatic conditions allowing the formation of extended peat-swamps, whereas the western sector is affected by seasonal and strong droughtness. ind of phytogeographic approach has proven useful for detecting some palaeogeographic problems, such as those involving the Patagonian subcontinent. In this regard, palaeogeographic reconstructions and palaeoclimatic models should be tested against these phytogeographic patterns.