Bread wheat is an allohexaploid (an allopolyploid with six sets of chromosomes: two sets from each of three different species). Of the six sets of chromosomes, two come from Triticum urartu (einkorn wheat) and two from Aegilops speltoides. This hybridisation created the species Triticum turgidum (durum wheat) 580,000–820,000 years ago. The last two sets of chromosomes came from wild goat-grass Aegilops tauschii 230,000–430,000 years ago.
Free-threshing wheat is closely related to spelt. As with spelt, genes contributed from Aegilops tauschii give bread wheat greater cold hardiness than most wheats, and it is cultivated throughout the world's temperate regions.