Extracted from:
https://en.wikipedia.org/wiki/Plum#Species:~:text=A%20plum%20is,and%20juicy%20flesh.
Plum is a fruit of a number of species in Prunus, subgenus Prunus. [1][2] There are many known species of plum and several that are grown commercially. Prunus domestica has been traced to East European and Caucasian mountains and is now referred to as European Plums. While Prunus salicina and Prunus simonii originated in China and varieties of these species are referred now to as Chinese, Japanese, or Asian Plums.
Plums may have been one of the first fruits domesticated by humans, with origins in East European and Caucasian mountains and China. They were brought to Britain from Asia, and their cultivation has been documented in Andalusia, southern Spain. Plums are a diverse group of species, with trees reaching a height of 5-6 meters when pruned. The fruit is a drupe, with a firm and juicy flesh.
Ploidy
Prunus simonii and Prunus salicina (Chinese or Japanese plums) have a diploid number of chromosomes (n=16) whereas Prunus domestica (European plums) have a hexaploid chromosome number (n=48). Chromosome number, as well as other factors, affect the ability of these cultivars to cross-pollinate one another. European and Asian plums do not cross-pollinate.
Many plums (European or Asian) are partially or fully self-fertile. Cross-pollination between cultivars is also quite dependent upon the dates of blooming such that early and late blooming varieties are unlikely to effectively cross-pollinate. In general, Asian plums bloom early in the spring and European varieties bloom in late spring.