PERMIAN PHYTOGEOGRAPHY IN GONDWANA

Phytogeographic patterns based on multivariate techniques (Multidimens ional Scaling) are proposed for the Permian vegetation of Gondwana. Th is approach requires a data set with broad geographic coverage based o n generic composition and with good time control. In general, strong p hytogeographic 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 S tage I(earliest Permian) the vegetation was strongly influenced by gla cial conditions; a very impoverished vegetation is seen except in Pata gonia and parts of South America. Four units were identified: Patagoni a, Nothosouthamerica, Australia and Indo-Africa. By far, Patagonia was the most diverse and had the most favourable climatic conditions, per haps 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 gla cial influence in the Brazilian sector. Indo-Africa had a much lower d iversity occupying high latitudes, whereas Australia had the lowest di versity 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 Sou th America (including a Brazilian and NW Argentinean unit) had the ric hest plant assemblages, whereas Africa, Indo-Australia and Antarctica (as separate units) are less diverse probably due to late glacial infl uence. By the late early Permian (Stage III), Gondwana shows much more ameliorated climatic conditions basically due to drifting into more t emperate latitudes, as well as increased moisture resulting in expansi on of peat-forming areas. This is immediately reflected in the vegetat ion as shown by diversified plant assemblages, even in Antarctica. Non etheless, a differentiation is again observed between eastern Gondwana (Patagonian and South American Units) and the western sector (Indo-Au stralian and Antarctic Units), whereas Africa would probably represent an ecotone. Beginning in the late Permian (Stage IV) there was a decr ease in the number of plant assemblages and diversity, indicating a de terioration in climate resulting from generally drier conditions. Lati tudinal differentiation can be observed, with Antarctica as a polar un it, Afro-Australia at high latitudes, whereas the South American-India n and Patagonian Units are located in middle latitudes. Finally, in Pe rmian Stage V (latest Permian) a South American Unit can be differenti ated clearly from the rest (Africa and Indo-Australia); Antarctica is interpreted again as a discrete unit. In the Stage V time slice easter n Gondwana returns to more humid climatic conditions allowing the form ation of extended peat-swamps, whereas the western sector is affected by seasonal and strong droughtness. This kind of phytogeographic appro ach has proven useful for detecting some palaeogeographic problems, su ch as those involving the Patagonian subcontinent. In this regard, pal aeogeographic reconstructions and palaeoclimatic models should be test ed against these phytogeographic patterns.