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Premise of the Study Reproduction in many crop species is impaired above 30 degrees to 35 degrees C; however, the sensitivity of reproduction in the natural flora remains uncertain. Studies focusing on the effect of high temperature on plant reproduction in wild species are necessary to improve our understanding of how rising global temperatures will impact global plant reproductive success and may ultimately inform models of plant distribution in the future. Additionally, these studies may highlight candidates for thermotolerance that could be further explored for crop improvement. Methods We studied reproductive heat tolerance in Trianthema portulacastrum, a weedy species found in hot microsites throughout the tropics and subtropics. Plants were grown at seven day/night temperature combinations: 30 degrees/24 degrees C, 33 degrees/24 degrees C, 36 degrees/24 degrees C, 40 degrees/24 degrees C, 44 degrees/24 degrees C, 24 degrees/40 degrees C, and 40 degrees/40 degrees C to study the effect of both high-day and high-night temperatures. The reproductive parameters measured include anther dehiscence, pollen viability, germination, ovule number, and seed set. Key Results Pollen viability and germination declined with increasing daytime temperature up to 44 degrees C, but this did not affect fruit production or seed set. Seed set was reduced under high night temperature. Continuous high temperature over the day and night (40 degrees C day/40 degrees C night) decreased pollen viability by half and reduced seed set by two-thirds. Conclusions Our results demonstrate Trianthema portulacastrum has much higher reproductive thermotolerance than commonly identified in crop species, and though inhibited, can retain fecundity at 40 degrees C. Through a combination of night escape and increased thermal tolerance, it maintains fertility in the hot microsites of its natural environment.