<P> Polyploidization is a mechanism of sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors . An example is the plant Erythranthe peregrina . Sequencing confirmed that this species originated from E. x robertsii, a sterile triploid hybrid between E. guttata and E. lutea, both of which have been introduced and naturalised in the United Kingdom . New populations of E. peregrina arose on the Scottish mainland and the Orkney Islands via genome duplication from local populations of E. x robertsii . Because of a rare genetic mutation, E. peregrina is not sterile . </P> <P> Polyploid types are labeled according to the number of chromosome sets in the nucleus . The letter x is used to represent the number of chromosomes in a single set . </P> <Ul> <Li> triploid (three sets; 3x), for example seedless watermelons, common in the phylum Tardigrada </Li> <Li> tetraploid (four sets; 4x), for example Salmonidae fish, the cotton Gossypium hirsutum </Li> <Li> pentaploid (five sets; 5x), for example Kenai Birch (Betula papyrifera var . kenaica) </Li> <Li> hexaploid (six sets; 6x), for example wheat, kiwifruit </Li> <Li> heptaploid or septaploid (seven sets; 7x) </Li> <Li> octaploid or octoploid, (eight sets; 8x), for example Acipenser (genus of sturgeon fish), dahlias </Li> <Li> decaploid (ten sets; 10x), for example certain strawberries </Li> <Li> dodecaploid (twelve sets; 12x), for example the plants Celosia argentea and Spartina anglica or the amphibian Xenopus ruwenzoriensis . </Li> </Ul> <Li> triploid (three sets; 3x), for example seedless watermelons, common in the phylum Tardigrada </Li>

Polyploidy in which all sets of chromosomes are from the same species is known as