by Jean Levy, National Collection Holder of Mentha
"Throughout the war years my elderly grandfather worked, in some capacity or other, for the Great Yarmouth Council, and one of the perks of his job was, apparently, a limitless access to cement. As a consequence of this privilege, my grandmother’s garden became increasingly replaced by concrete so that, by the time of my mother’s annual trips home to visit relatives, all that remained of nature in that Norfolk garden was a small patch of earth, probably six foot square, in which my grandmother religiously cultivated mint.
That small aromatic patch was where I played and, as I played, my childhood fantasies were acted out upon a menthol-soaked blanket of trodden mint. Now, sixty years later, the scent of crushed spearmint still evokes holiday memories of scary aunts, sandcastles and cucumber sandwiches.
It was, therefore, quite inevitable that, as an aspirant middle-aged taxonomist in search of a project, I should alight upon the genus Mentha. I felt that, after such a baptism, I must already know the subject well. Little did I know my folly. I carried out some preliminary research and concluded that, yes indeed, the genus was in urgent need of assessment. I visited garden centres, collected ancient floras, befriended elderly gentlemen, grubbed around in the undergrowth, and thereby I started to accumulate varieties. Five years into the project, with around fifty cultivars established, I began to feel that I had bitten off more than I could chew.
Essentially, Mentha is reported as having anywhere between 10 and 25 distinct species worldwide, although the biological identity of these species is doubtful, often fanciful. It is clear that individual species within this complex hybridize freely. Indeed, many of the recognized species would seem themselves to have arisen by interspecific hybridization followed by polyploidy and genetic stabilization. For example, spearmint M. spicata is thought to have originated from a cross between M. suaveolens and M. longifolia, with two subgroups, M. spicata subsp. spicata and M. spicata subsp. glabrata, indicating a morphological and aromatic tendency towards one or other of the parent species.
Separate cytogenetic studies have revealed the spicata complex as having two major cytotypes (2n = 36 and 2n = 48) but these have not been convincingly correlated with the subgroups. Similarly, black peppermint, M. x piperita, is believed to have arisen from a cross between water mint, M. aquatica, and the hybrid M. spicata. Accordingly M. x piperita is recorded as having two corresponding cytotypes (2n = 66 and 2n = 72). An additional species, M. arvensis, the field mint, has joined this complex, hybridizing with M. spicata to produce the ginger mint, M. x gracilis, and at some point the intrusion of the M. aquatica genome into this arvensis x spicata hybridization produced the stable hybrid M. x smithiana, or red mint – a truly stately variety. These various stable hybrids may well hybridize with either of the parents so that, for instance M. villosa is regarded as a backcross between M. spicata and M. suaveolens. These backcrosses may be sterile or subfertile but they are able to persist by vegetative propagation.
Over the last few decades horticulturists have fallen upon this Mentha complex and have developed and promoted a vast range of different varieties. Over the last twenty years mint has become one of those plants that people collect and collectors’ interests have extended beyond the traditional apple mints (suaveolens derivatives) and silver buddleia mints (longifolia derivatives). New cultivars have been imported into the indigenous British gene pool, and the diverse morphology of these new varieties has added to the taxonomic burden. In the last decade hybrid varieties such as Asian, Hillary’s Sweet Lemon, Julia’s Sweet Citrus, Algerian Fruity, Moroccan, Swiss Ricola, and Betty’s Slovakian have been added to the RHS list, with British plant hunters adding Tashkent, Newbourne, Guernsey and so on. I have a few of my own collected from around the UK but I see no point in adding mine to the confusion.
Often the provenance of these new listed varieties is difficult if not impossible to determine. Were M. spicata ‘Greek’, M. spicata ‘Austrian’ and M. spicata ‘South of France’ collected from the wild or were they purchased from supermarkets or garden centres all of which might have imported them from Belgium or Holland . . . or even the UK? They all look pretty much the same. And the names of these new varieties, officially listed, reveal their incompatibility with the existing taxonomy: M. ‘Berries and Cream’, M. ‘Sweet Pear’ and M. Verona declare no taxonomic affinities.
In addition to the confusion caused by widespread hybridization, both natural and artificial, the identification and classification of this burgeoning Mentha complex is made more difficult due to extrachromosomal factors. Many of the new varieties are distinguished by morphological characteristics which may well be controlled by non-chromosomal genes. Obvious examples are the variegated mints, M. x piperita ‘Logee’s’, and M. spicata ‘Small Dole’ (possibly synonymous with M. spicata ‘Variegata’, also listed by RHS). The variegation in both of these varieties would seem to be extra-nuclear so that often a perfect variegated plant reverts to non-variegated foliage whilst perennating. I dare to suggest that other less obvious characteristics might be inherited in this manner, so that what dies back in the winter might not, absolutely, resemble what reappears in the spring. It all pivots upon the distribution of genes in the underground stems. Incidentally, the variegation seen in the variegated apple mint M. suaveolens variegata, sometimes referred to as pineapple mint, is a far more stable affair.
Vegetative propagation of selected stems remains the most effective way of maintaining the genetic integrity of a particular Mentha variety. But when combined with self-seeding this disappearing underground has another consequence for the harassed taxonomist. Having a hybrid gene pool, there is little likelihood that varieties might breed true, so that seed (nutlets) if produced may well fall into the mass of stems that are dying back for the winter. New seedlings will then contaminate, even over-run the parent plant.
This situation could be controlled by isolating plants if self-fertilization is not likely or cutting off the flowers, which is undesirable and also reasonably impossible with a collection of 250+ cultivars in triplicate, which is the stage I have reached with my collection. Could this be too many, I ask myself? Certainly in the early days a new self-seeded, slightly unusual plantlet was a blessing . . . now I find myself dreading finding any mint-like seedling in the shingle around the Mint House. But when I do it’s still a tiny blessing . . . even if I’m not sure who its parents are.
At this point one can see the clear need for accurate recording of morphology, not only photographic but also via a revival of those wonderful old accurate words like decussate and acuminate and protogynous that modern botany seems increasingly to eschew. I had a dream at the beginning of this whole taxonomic exercise that I would take this difficult genus, and classify it according to its morphological characteristics . . . the way taxonomists used to in those halcyon days of field botany. I have watched with frustration the slow dissolution of those skills as they are replaced by ripping a plant from the ground, crushing it, dissolving it, centrifuging it and converting its remains into chromatographic patterns or protein patterns in electrophoretic gels.
But, after twenty-five years, I have to admit that the genus I love is working against me on this one. So perhaps a hybrid approach is necessary: I’ll concede that biochemists provide answers as long as they look at the plants before they squash them. I am now, as a new collection holder, preparing myself to open my collection next year, to the public. I look forward to this with trepidation. Not only do I fear each year that every single one of my plants will die back and never reappear in the Spring (an unnecessary paranoia), but also I have nightmares that people will come bearing pocket-sized secateurs and help themselves to small pieces of my mints until they become little bald stumps (this might be the way I myself have acquired certain varieties in the past).
I am also bracing myself for questions such as “Aren’t all mints the same? . . . Which one do you use for mojito? . . .” and my all-time favourite, “Why don’t you collect plants with flowers?”
Meanwhile I will continue to nurture my charges and catalogue their activities And if anybody has a mint from Norfolk, I’d be very grateful for a cutting. It would seem to be a hole in my collection."