Chocolate mint is a mint closely related to peppermint (Mentha x piperita), and it has a chocolate aroma. It is a sterile hybrid which means it doesn't set seed, and therefore can't be grown from seed. Let's have a look at why this is so.
Not only is chocolate mint a hybrid, it is also a cultivar (a cultivated variety). This means it is a plant produced by many generations of selectively crossing and hybridising other mint species.
These types of plants are usually infertile because the focus of producing a cultivar is on retaining and reproducing various desirable characteristics, in this case the chocolate aroma, and during the hybridisation process the chromosomes responsible for fertility and viable reproduction frequently become lost. Any offspring is usually sterile so they can only be reproduced by cloning the plant via cuttings or root division.
It is also difficult to track the classification and naming of the genus Mentha because many species hybridise readily with each other, or are themselves the result of sometimes ancient hybridisation events. Such hybrids may sometimes produce seed but give rise to variable offspring, so the resulting plants may not have the desirable characteristics of that particular hybrid.
If we look at chocolate mint's Latin name you'll get an idea of how this plant came about and see that it is a highly hybridised plant.
Chocolate mint, Mentha x piperita f. citrata ‘Chocolate’, indicates that it is a hybrid formed by a crossing of peppermint (Mentha x piperita) and orange mint (Mentha aquatica var. citrata).
Peppermint, as indicated by the x in its name Mentha x piperita, is itself a hybrid of two species namely Mentha spicata (spearmint) and Mentha aquatica (watermint).
Orange mint is a cultivated form or variety of Mentha aquatica, namely Mentha aquatica var. citrata, which has already been selected for various aromatic qualities.
Chocolate mint therefore ends up having at least three hybrid parents in its lineage, so it is not surprising that the resulting 'chocolate' cultivar ends up being a sterile hybrid.
As a sterile hybrid, peppermint and its cultivars such as chocolate mint cannot be propagated by seed, although they will grow very easily via cuttings or root division, and propagating plants like this means you will get an exact replica of the plant including all its desirable properties.
Like other mints, chocolate mint is vigorous and spreads quickly via rhizomes, so if you wish to keep it contained then it is best grown in a pot. It gets up to 60cm tall, and has rounded lance-shaped leaves that are slightly darker green than other mints. Stems are reddish purple and lilac-purple flowers appear in summer.
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Some of chocolate mint's parents. Clockwise from top left: Water mint (Mentha aquatica), peppermint (Mentha x piperita), and spearmint (Mentha spicata)
