The Wealthy apple is genetically related to the Haralson, though it took DNA testing to rediscover this fact after extensive hybridization.

The species is threatened by extensive hybridization with the invasive White Mulberry (M. alba), introduced from Asia.

Its eastern limit in Russia is hard to define, due to extensive hybridisation and intergradation with the Siberian spruce, but is usually given as the Ural Mountains.

For a plant with extensive natural hybridization amongst varieties and the reportedly high genetic divergence, these values are thus indicative of the wide range of diversity.

However, blue mussel populations show extensive hybridisation worldwide and are a well studied example of a marine hybrid zone.

If the isolating mechanisms between these populations are only partially complete, extensive hybridization may occur.

However, extensive wolf-dog hybridization is not supported by morphological evidence, and analyses of mtDNA sequences have revealed that such matings are rare.

The problem of its species status and placement in the genus is complicated by extensive natural hybridization with Tilia americana.

Edinburgh University found, in Scotland, there has been extensive hybridisation with the closely related sika deer.

There is now serious concern for the long-term genetic viability of red mulberry because of extensive hybridization in some areas.