Fire has been shown to stimulate seed germination in a number of fire-prone ecosystems, mainly in Mediterranean type shrublands and, though not exclusively, in hardseeded species. Stimulation by heat, or by chemical constituents of charred wood and smoke, have been identified as the main mechanisms breaking dormancy of soil-stored seeds. In this study, we experimentally tested the effect of heat on germination rates of nine herbaceous species (5 grasses, 1 Cyperaceae, 3 forbs) from frequently burned grassland in southern Brazil. Seeds were exposed to temperatures between 50ºC and 110ºC (to 180ºC for two species) for 2 min. Germination of treated seeds was monitored in a germination chamber. The heat treatments did not stimulate germination in any of the species tested. Tolerance of seeds to heat varied between species. Two of the herbs and the three grasses with the smallest seeds were able to germinate at temperatures of 110ºC, or even higher. Apparently, no mechanisms directly stimulating germination by heat have developed in herbaceous species from southern Brazil. However, survival of high temperatures can be considered to be an adaptation to fire, possible allowing for increased germination in the post-burn environment. © Springer 2005. Abstract reproduced by permission.