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A new research paper I co-authored has just been published, Towards a taxonomic revision of Tradescantia subg. Campelia (Commelinaceae) I: sectional arrangement and revision of T. sect. Rhoeo. It’s open access (free to read) here. This article will explain the results from the paper that are most relevant for tradescantia growers and hobbyists.
Background
This new research paper is intended as the first in a series. Altogether, that finished series will be a taxonomic revision of the Campelia subgenus.
A taxonomic revision is a major study which reorganises and clarifies the identities and relations of all the species in a particular group. Most research studies on new or reclassified species only focus on one or a small number of species in isolation. This means that over time, the relationships between them can become confusing, disorganised, and inconsistent. A taxonomic revision takes a large-scale overview to make sure all those relationships are clear and up to date.
The Campelia subgenus is a particular subgroup of Tradescantia species which includes T. zebrina, T. zanonia, T. spathacea, and lots of others which are less common in cultivation. It’s quite a complex subgroup, with a lot of smaller sub-subgroups inside it, so the whole revision is too much for a single research paper. This new papers covers just the section Rhoeo, which previously only contained one species: T. spathacea.
The paper gives detailed descriptions of the Rhoeo section, including the species inside it and the cultivars inside those. If you take a look at the full paper you can see all the interesting details like distribution maps and pollen analysis. But there are two big results that will be the most interesting to tradescantia growers:
- Tradescantia concolor is a separate species now.
- The miniature cultivars are called the Bantam Group now.
Read on for more explanation of each of those results.
Tradescantia concolor is a separate species now
The first publication of this plant was as a botanical variety, Tradescantia discolor var. concolor (Baker, 1868). Then a century later it was reclassified as a form, Rhoeo spathacea forma concolor (Stehlé, 1970). Most recently, both of those names were considered synonyms for the species T. spathacea (POWO, 2022), and so ‘Concolor’ was treated as a cultivar.
The main apparent difference between ‘Concolor’ and other forms of T. spathacea was the colour of the leaf undersides – silvery-green in ‘Concolor’, purple in other T. spathacea. So it was considered a simple colour variation, only interesting for horticultural purposes.
The new paper has changed the situation once again. The research found that there are significant differences between ‘Concolor’ and other T. spathacea. They grow in different environments, have microscopic differences in pollen and flower structure, and they have never been known to hybridise. Because of all this, the new paper has reclassified ‘Concolor’ as a species of its own, a sibling in the Rhoeo section: Tradescantia concolor.
The species Tradescantia concolor doesn’t have many cultivars of its own. In fact, there’s only one, and it’s probably extinct. A catalog from the nursery Glasshouse Works (1984, p. 17) mentioned a ‘Vittata’ form of T. concolor, variegated with yellow stripes. The cultivar doesn’t seem to have been documented any time since then, so it’s most likely lost. So far, all the T. concolor in cultivation are unnamed wild types.
This means that if you have a specimen labelled Tradescantia spathacea ‘Concolor’, you can update your label to Tradescantia concolor. Now rather than a particular cultivar of one species, it’s considered the natural form of a different species.
The miniature cultivars are called the Bantam Group now
There are currently six named cultivars of Tradescantia spathacea. The oldest, T. spathacea ‘Vittata’ (not to be confused with the T. concolor ‘Vittata’ mentioned above!) is a full-sized plant identical to the wild type except for its yellow stripes. All five of the others are miniature forms which are about half the size of the natural species.
‘Vittata’ is rare in cultivation today, so a lot of growers are only familiar with the miniature types, and might not even realise that they are miniature. But full-sized forms of T. spathacea actually have leaves growing to more than 30cm long, whereas the common cultivars have leaves generally less than 15cm long.
It’s most likely that all of these small cultivars share a common origin of a single dwarf mutation from the wild species. They all have different variegated colours and patterns, but identical growth habits. In cultivation they sometimes mutate from one pattern to another, and that’s probably how each of the different cultivars originated to begin with.
Because of how similar and closely-related they are, it’s useful to have a way to distinguish them from ‘Vittata’ and the large wild form – and any other full-sized cultivars that might arise in future. So the new research paper has established a cultivar group name for them: the Bantam Group. It’s named after the miniature breeds of domestic fowl like chickens.
The names of the individual cultivars haven’t changed. So if you have a plant labelled T. spathacea ‘Sitara’, that name is still correct. But if you want to be even more precise, you could instead label it T. spathacea (Bantam Group) ‘Sitara’. And if you have a plant which you know is one of those small types, but you can’t tell which one because it’s been growing in the shade and the stripes are all faded and it’s looking a bit sickly after a tough winter… you can say that it’s something from the T. spathacea Bantam Group.
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References
Baker, J. G. (1868). “Natural Order Commelinaceae”. In Saunders, W. W., Refugium Botanicum (Vol. 1) (tab. 48). John Van Voorst. Biodiversity Heritage Library link.
Stehlé, H. (1970). Notes taxinomiques et écologiques sur des Monocotylédones nouvelles ou rares des Antilles françaises: Commelinaceae [Taxonomic and ecological notes on new or rare Monocotyledons from the French West Indies: Commelinaceae] (37e Contribution). Bulletin de la Société Botanique de France, 117:1-2, 71-80. doi:10.1080/00378941.1970.10838746. PDF link.
Glasshouse Works. (1984). [Catalogue]. UC Davis Library.
POWO. (2022). Tradescantia discolor var. concolor. Plants of the World Online. Link.
Pellegrini, M. O. O., Hunt, D. R., Grant, J. R., Rowe, A., Antonio-Domingues, H., de Almeida, R. F. (2026). Towards a taxonomic revision of Tradescantia subg. Campelia (Commelinaceae) I: sectional arrangement and revision of T. sect. Rhoeo. Plant Ecology and Evolution 159(2): 208-227. doi:10.5091/plecevo.138752. Open access link.