Wild moth orchid species that are yellow or are fragrant are "diploid" -they have two sets of macrochromosomes-whereas the large-bloomed hybrid cultivars now on the market are "tetraploid," having four sets of microchromosomes. The vast differences in the number and size of the chromosomes makes it difficult to crossbreed them.
由於蝴蝶蘭中黃花或帶有香味的「原生種」多是 2 倍大型染色體，而目前市面上大花型的「栽培種」則為 4 倍小型染色體，染色體的倍數不同、大小迥異，難以配對雜交（即「不親和」）。