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Ok, je vous tiendrai au courant ici, sur ce topic.
En attendant lisez ! :
http://pt.wikipedia.org/wiki/XaximINTRODUCTION
Xaxim (Dicksonia sellowiana Hook. is a tree fern which belongs to the Dicksoniaceae family, and i is widely distributed in Latin America (Sehnem, 1978; Tryon and Tryon, 1982). Its trunk can reach up to 5m in height and 50cm in diameter (Pio Corrêa, 1931) and it is totally surrounded by a wide hem constituted by entangled foreign roots (Fernandes, 1997). This trunk is used as raw material for vases, and the substratum is used in the production of ornamental plants.
The intense harvesting of its trunks has caused the inclusion of this species in Appendix II of CITES (MMA, 1998) such as endangered species. In spite of this, few studies have actually been carried out since studies that could provide information about conservation strategies and management in Pteridophytes are more complex and difficult to interpret than those regarding flowering plants. This is due to the fact that these plants have in their cycles two free life phases: a gametophytic phase and a sporophytic phase. These phases are very distinct with regard to their morphology, physiology, and biotic and abiotic relationships. They have different ecological requirements, because a specific environmental situation that is favorable to the gametophytes can be inappropriate for the sporophytes. This environmental situation cannot persist for the gametophitic and sporophytic phases since it propitiates the action of selective forces separately in each phase (Dyer, 1979; Soltis and Soltis, 1989; Ranal, 1999).
Many Pteridophytes, such as Xaxim, can present the capacity of formation of spore banks, as well as the dormancy of some spores (Schneller, 1998; Ranal, 1999; Filippini et al., 1999; Rooge et al., 2000) that can guarantee the individuals' germination at different times, making possible the decrease of the competition in the initial phases of development and increasing the chances of reproductive success of parental genotypes. Therefore, the recognition of variations in the behavior patterns between individuals and natural populations is important because it can indicate the existence of adaptative strategies in the initial phase of development and fixation of the gametophytes, which are reflected directly in the ability to colonize, the reproductive success, and the maintenance of the parental genotypes.
Although this kind of information involving the autoecology of tropical Pteridophytes and their intra and interspecific interactions in natural habitats is extremely important, it is practically not available. In this context, the objective of this study was to analyze the existing variability in the germination of individuals' spores collected from two natural populations of Xaxim (Dicksonia sellowiana) in southern Brazil.