Hemileia vastatrix is a fungus of the order Pucciniales that causes coffee leaf rust (CLR), a disease that is devastating to susceptible coffee plantations. Coffee serves as the obligate host of coffee rust, that is, the rust must have access to and come into physical contact with coffee in order to survive. There is no cure at the moment, although farms have managed to reduce their impact by replanting infected farms with hybrids that have a strong genetic resistance to rust.