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Seed dormancy and germination have been studied in the genetic model Brachypodium species complex in cooler, moist higher latitudes. Studying environmental factors in arid mountains affecting dormancy and germination in Brachypodium complex could determine the factors controlling these processes. This study assesses the impacts of temperature during seed maturation, seed after-ripening, drought, photoperiod, and thermoperiod on final germination and germination rate index of B. hybridum in the Arabian Desert. Seeds were germinated under dark or light conditions and under different ratios of red:far-red light, with three diurnal thermoperiods. The final germination percentage was significantly greater at 15/25 degrees C and 20/30 degrees C than at 25/35 degrees C and in light rather than in darkness. Seeds that reached maturity at 15/25 degrees C attained greater germination rates and faster germination than those that reached maturity at 20/30 degrees C. One-year after-ripening enhanced the final germination percentage and reduced photoperiod requirements. Light quality did not affect final germination percentage. The seeds tolerated drought of up to -0.8 MPa polyethylene glycol. The tolerance of B. hybridum seeds produced at higher thermoperiods to moderate levels of osmotic stress and their higher dormancy indicate that this species has the potential to survive the projected global warming in its native and introduced ranges.