Hybrids: Basic Questions about Mint Plants

I have a question about hybrids. Specifically, I'm interested in knowing about peppermint (Mentha x piperita). I have read that this plant is a cross between spearmint (M. spicata) and watermint (M. aquatica). I have also read that because peppermint is a hybrid, it is sterile and cannot produce seeds. Yet I can find peppermint seeds for sale.

Assuming that commercially-available peppermint seeds will grow into true peppermint when planted, I am curious to know how the seeds are produced?

If the answer is that M. aquatica is pollinated by M. spicata (or vice versa), does it make a difference which plant pollinates the other? Or is the resultant peppermint the exact same either way?

And if that’s not how the seeds are produced, then what is the correct answer?

Also, somewhere I've seen reference to "white" and "black" peppermint plants. Are there really such varieties -- and, if so, what makes them "white" and "black"? Or is there just one true peppermint?

 

Mint article for you to read -- looks like a case of buyer beware when it comes to the sale of "peppermint seeds".

 

Ｔｈａｎｋ you for the link to Conrad Richter's article about mint. Richter writes:

In addition, here is what I have discovered from other sources.

Peppermint (Mentha x piperita) is indeed sterile. It is a triploid hybrid, so it cannot be bred by natural sexual crossings. It's unable to produce normal gametes because, as a triploid, its three sets of chromosomes are unable to form pairs and separate during meiosis.

However, by treating peppermint with a drug called colchicine, the ploidy can be doubled and fertile hexaploid plants can be produced. In fact, it seems that such "polyploidization is a widespread method used in peppermint breeding to increase the chromosome numbers and to restore the fertility" (F. Pank et al, 1999).

As for what constitutes "true" peppermint, it seems there is no simple answer. I have found scientific descriptions of peppermint saying that "chromosome number is variable", and indeed I have found somatic counts of 48, 66, 72, 84 and 120 for non-colchicine induced plants. The most commonly cited number seems to be 72. And for colchicine-induced plants, I've found counts of 90(!), 96, and 144.

Getting back to the peppermint seeds I see at local stores, I still wonder what they are. Are they from colchicine-treated hexaploid plants? Or are they simply the seeds of some other mint species being sold as peppermint?

 

A local store was selling this as "peppermint", although I found that it tasted like a very blah type of spearmint.