I have been asked by someone, who is an experienced gardener, to explain the various terms used when discussing species and cultivars. As she says, "I never needed to know about them when I was digging! Now I'm more interested in the theory, but it's confusing, and, why are some of the terms interchangeable?"The basic terms are not interchangeable, each is clearly defined, and when people refer to varieties in one breath and hybrids in another, then it is obvious that the speaker is either confused, or is using non-botanical meanings. There are long, internationally defined rules for the naming of species and garden cultivars.
Species
The Canna family is sub-divided into approximately 20 separate species. They are all distinctly different, but theoretically they share a common ancestor in the dim and distant past. Species names are always written in italics, to differentiate them from garden cultivars, e.g. Canna indica.
In the wild, species (shorthand sp.) are more or less uniform in habit, foliage, flowers and fruit. Any variation is part of an evolutionary process, and botanists apply subdivisions within a species (sub-species, varietas, and forma) to recognise such differences. All remain more or less stable in the wild, but when grown together in cultivation they may hybridise and the distinctions become blurred. This variation is exploited by gardeners who select (recognise and name) an individual plant, and propagate to maintain it.
In the wild, species (shorthand sp.) are more or less uniform in habit, foliage, flowers and fruit. Any variation is part of an evolutionary process, and botanists apply subdivisions within a species (sub-species, varietas, and forma) to recognise such differences. All remain more or less stable in the wild, but when grown together in cultivation they may hybridise and the distinctions become blurred. This variation is exploited by gardeners who select (recognise and name) an individual plant, and propagate to maintain it.
Sub-species
A sub-species (shorthand ssp.) is a “mini-species” with distinct morphological or genetic variation, and a sometime distinct geographical distribution. I don't believe that Canna have any defined sub-species, certainly not in Dr Tanaka's revision of the Canna species.
A variety (or varietas, shorthand var.) is a wild variety, and its differences from the species are less clear-cut than a sub-species, e.g. Canna indica var. maculata.
Form
The form (or forma, shorthand f.) is used for colour variations or similar minor differences.
Hybrid
If several species of one genus are cultivated together, they may hybridise (shorthand x), giving rise to offspring sharing characters of both parents, for example Canna x ehemanni (C. iridiflora x C. indica var. warsczewiczii). Seedlings from these crosses may vary, and may be selected and given cultivar names. If the resulting hybrids are fertile, several generations of plants may be produced. In time, the parentage of the offspring becomes obscured, reflected in the style of names chosen, for example Canna ‘Ehemanni’.There are also variations, when we refer to F1 and F2 hybrids, but those require a separate explanation as we are then categorising genetic variation.
A cultivar is an artificially raised or selected plant (the name being a contraction of cultivated variety) that is clearly distinct, uniform, and stable in its characteristics, and able to be maintained by propagation. Some cultivars are increased vegetatively (asexually, also referred to as cloning) from an individual plant, and are maintained by this method. Other cultivars are raised from seed (i.e. sexually) and their characteristics can only be maintained by removing all plants not true to type (removing rogues). If rigorous selection is not carried out, plants sold under those cultivar names may not have the expected characteristics. In the main, Cannas carry the DNA of such a mixture of colours, shapes and other characteristics that roguing is impractical, and the advice given by all authorities is to treat each seedling as a separate and distinct cultivar.
Sports
Sports are mutations resulting from genetic change, which produce shoots or flowers differing from those of the parent plant. If a mutation is propagated vegetatively it may be named as a cultivar and maintained – many variegated plants occur this way. Not all sports are stable; some often resort to the parent’s characteristics, e.g. C. ‘Stuttgart’, top picture, is said to revert to C. ‘Omega’, right picture.
Conclusions
There is no rocket science about this terminology, it is just a simple and straightforward way of classifying our wild and garden raised plants.
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