Seed germination of Xyris spp. from Brazilian campo rupestre is not associated to geographic distribution and microhabitat

Xyridaceae comprises the seventh largest monocot family in Brazil, with Xyris L. being the largest and most representative genus there. The most important center of diversity for this genus is the Espinhaço Range in southeastern Brazil, where these plants grow in rocky open fields (campo rupestre), usually on humid or boggy soils. The present work examined the seed germination of Xyris species to evaluate the relationships between the germination requirements and their geographic distribution patterns and the distinct micro-habitats they occupy. Laboratory tests were carried out to evaluate light, temperature, and oxygen restriction effects on the germination of eight Xyris species occurring in the Espinhaço Range. All eight species had small seeds that were intolerant of high temperatures (≥35 °C) when imbibed, absolute light requirements for germination, and were able to germinate under hypoxic conditions. The effects of temperature on seed germination do not explain the patterns of geographic distribution nor the endemism seen among the species examined here. Additionally, the occurrence of Xyris species in soils with different water retention capacities cannot be attributed to the capacity of their seeds to germinate under conditions of hypoxia, as the seeds of species that occur on well-drained soils also germinated under low-oxygen condition.