bio

Allopolyploidy

New species formation by hybridising two species and then doubling the hybrid's chromosome set, which makes it fertile and instantly isolated from both parents. This is not theory: the salt-marsh grass *Spartina anglica* appeared in Britain around 1890 in exactly this way, and *Tragopogon miscellus* in North America did the same in the twentieth century, twice, in different places. An allopolyploid species has two parent lineages, so on a strictly bifurcating tree diagram there is nowhere to draw it.