The apricot, Prunus armeniaca, is a species of Prunus, classified with the plum in the subgenus Prunus. The native range is somewhat uncertain due to its extensive prehistoric cultivation. The apricot is a small tree, 8–12 m (26–39 ft) tall, with a trunk up to 40 cm (16 in) in diameter and a dense, spreading canopy. The origin of the apricot is disputed. It was known in Armenia during ancient times, and has been cultivated there for so long, it is often thought to have originated there. Apricots are susceptible to numerous diseases whose relative importance is different in the major production regions as a consequence of their climatic differences. Diseases include bacterial canker and blast, bacterial spot and crown gall, and an even longer list of fungal diseases, including brown rot, black knot, Alternaria spot and fruit rot, and powdery mildew. Other problems for apricots are nematodes, viral and phytoplasma diseases, including graft-transmissible problems.