This is a topic that causes a lot of confusion, so I wrote this summary on correct and incorrect names in Commelinaceae! For a more detailed explanation of the different systems of plant naming, you can read this in-depth article. And for an even shorter version, you can skip straight to the slide summary at the end.
Scientific names
These are names botanists make, to classify wild plants. A species name (e.g. Callisia gentlei) always has two parts – the genus (Callisia) and the species (gentlei). Sometimes scientists make groups within the species, such as a variety – this is a third part written with the abbreviation var. after the species name (e.g. Callisia gentlei var. elegans). To help distinguish them, scientific names are usually italicised and in latin. The rules for creating these names are defined in the ICN.
For a scientific name to be valid, it has to meet some strict requirements:
- It has to follow some complicated rules about formatting and latin grammar
- It has to have a description which is detailed enough to distinguish it from any other plant
- It has to have a preserved sample of the plant that shows its identifying characteristics
- All of that has to be published in hard copy somewhere publicly accessible (e.g. a scientific journal)
Those requirements are difficult to meet! That’s to make sure that new names are only made if they’re useful and accurate at describing a real, wild kind of plant. If a name doesn’t have a published description and a sample so that others can verify it, it’s not accepted.
Cultivar names
These are names made by plant growers, to classify cultivated types of plant (grown deliberately by humans). Every cultivar came from a wild plant at some point in history, so it should always have the correct scientific name for the genus it comes from. The species can be included as well if it’s known for sure, but it isn’t a requirement.
So a full cultivar name (e.g. Callisia repens ‘Rosato’ or Callisia ‘Rosato’ – both are acceptable) has two parts – the scientific name (Callisia repens or just Callisia) and the cultivar itself (‘Rosato’). To distinguish them, cultivar names are always capitalised and in ‘single quotes’, and they should generally not be in latin. The rules for these names are defined in the ICNCP (and you can read a plain english version here).
For a cultivar name to be valid, it has to meet some requirements too – but they aren’t as strict as for scientific names:
- It has to follow some rules about format and words that aren’t allowed
- It has to have a description which can distinguish it from similar cultivars
- It has to be published in hard copy somewhere publicly accessible (e.g. a nursery catalog or a gardening journal)
Those requirements are not too hard to meet. That’s to make sure that anyone who grows a new type of plant should be able to give it a valid cultivar name fairly easily.
Some invalid names which are often used in Commelinaceae
Unfortunately, there are a lot of names which don’t follow these rules. People are often tempted to make up scientific-sounding names for cultivated plants – when actually that’s the complete opposite of what we should do! Instead we should make sure the scientific names we use are correct and valid for the wild ancestors of our plants, and make cultivar names when we need to identify different cultivated plants.
The easiest way to check whether a scientific name is valid is to search a database like POWO. It’s maintained by an international botanical authority and keeps track of all valid published names, so that we don’t have to.
Here are some examples of widespread scientific-seeming names used for Tradescantia plants which are invalid:
- Tradescantia zebrina discolor ❌ This is written as if it’s a scientific name, but it’s formatted wrongly – if it’s a botanical variety is should have the var. abbreviation in the middle.
- Tradescantia zebrina var. discolor ❌ This is correctly formatted for a scientific name. But a quick search on POWO finds that it’s not actually an accepted name at all. It’s never been published with a scientific description and reference to samples of wild plants, so it doesn’t meet the requirements to be a valid botanical name.
- Tradescantia zebrina ‘Discolor’ ✅ Since it’s not a scientific name, but it is a distinct cultivated plant, it should be written as a cultivar name instead. It belongs to the wild species Tradescantia zebrina, and the cultivar itself is called ‘Discolor’.
- Tradescantia albiflora ❌ This is in the correct format for a scientific name. But searching POWO finds that this is considered a synonym for Tradescantia fluminensis, so that’s the correct name to use.
- Tradescantia fluminensis ✅ The correct accepted name for the species, in the right format.
- Tradescantia albiflora variegata ❌ The wrong format for a scientific name, and the first part of the name is not an accepted species.
- Tradescantia ‘Albiflora Variegata’ ✅ It’s a distinct cultivated type, so the identifying part should be written as a cultivar name.
- Tradescantia mundula variegata ❌ Again, this is written like a scientific name but in the wrong format. If it’s supposed to be a botanical variety, it should have the var. abbreviation to specify.
- Tradescantia mundula var. variegata ❌ Correctly formatted, but a quick POWO search finds that it’s not an accepted scientific name. It has never been published with a description and wild samples, so it doesn’t meet the requirements.
- Tradescantia mundula ‘Variegata’ ❓ This one is a grey area. It’s correctly formatted to be a cultivar name and so it could be acceptable. But in fact the name ‘Variegata’ has only be used very recently, and according to the rules, new cultivar names can’t be in Latin.
- Tradescantia mundula ‘Rainbow’ or ‘Tricolor’ ✅ Correctly formatted as a cultivar, and it uses a valid non-Latin cultivar name (haven’t confirmed for sure which name is valid yet, but it’s definitely not ‘Variegata’!).
- Tradescantia zebrina variegata ‘HappiLee’ ❌ The first part is written like a scientific name but it’s in the wrong format. If it’s supposed to be a botanical variety, it should have the var. abbreviation to specify.
- Tradescantia zebrina var. variegata ‘HappiLee’ ❌ Now the scientific name is written in the right format, but a quick POWO search finds that there is no botanical variegata variety at all. It should be removed and the name written with just the species.
- Tradescantia zebrina ‘HappiLee’ ✅ Correctly formatted with the scientific name for the species, no made-up botanical variety, and the correct cultivar name.
In fact the same goes for almost any plant which is written with “variegata” as if it’s a scientific name. All of those plants should actually have non-Latin cultivar names to identify them correctly.
Sorting out the mess of Tradescantia names will take a long time and a lot of work – many plants might have to get completely new names in order to follow the rules. But hopefully, eventually, we could have a system that lets us unambiguously identify all our favourite plants and follow the best practises that scientists and horticulturalists around the world have agreed on!