The tangled history of the Tradescantia Andersoniana Group

T. Andersoniana Group plant with grassy leaves and purple flowers

There are several closely-related Tradescantia species which are native to temperate North America. They form mounds of long grassy leaves, topped with small blue or pink flowers. The number and classification of these species has changed a lot over time, as botanists studied wild plants and learned about their differences and similarities.

At the same time, they have become popular in cultivation – in their native North America, as well as introduced to Europe. They are frost-hardy and grow as deciduous herbaceous perennials, perfect for temperate-climate gardens. These cultivars have been developed into many shapes and sizes, with all kinds of different flower styles and colours.

This group of plants – like so many tradescantias – have a history of confused identity. In this article I’ll cover their history over the last hundred years, as the name went from Tradescantia virginiana, to Tradescantia × andersoniana, and finally to the Tradescantia Andersoniana Group.

Tradescantia virginiana

The most common and well-known temperate species is Tradescantia virginiana. Historically, almost all garden cultivars of Tradescantia were labelled as this species. Gardeners and nurseries don’t generally care much about being precise with species identities. T. virginiana is common and widespread, and at a glance it was the obvious choice for the wild ancestor of these garden plants.

Then early in the 20th century, botanists Anderson and Woodson (1935) wrote a book about the native temperate Tradescantia species. Their focus was on the plants as they occurred in the wild, but they made a passing mention of garden cultivars that threw their identity into question:

It is a notable fact that the senior author has never seen a Tradescantia virginiana in a European garden which could unhesitatingly be referred to that species. Most of the plants in cultivation under that name show unmistakable evidence of mixture with T. canaliculata [T. ohiensis] and T. subaspera.

Andeson & Woodson, 1935, p. 30

There was not a single garden cultivar that actually belonged to the species T. virginiana. Instead the authors believed that every single garden cultivar had hybrid ancestry, and also included the related species T. ohiensis (known as T. canaliculata at the time) and T. subaspera.

About twenty years later in another book, Anderson (1952, Chapter 2) wrote in more detail about how they had come to that conclusion. During their initial research, they had collected samples of wild plants to grow them in an experimental garden. And they found that when cultivated like this, the species T. virginianaT. ohiensis, and T. subaspera were all incredibly prone to hybridisation. These hybrid seedlings were more vigorous and attractive than their wild parents, so they would certainly be selected and maintained by gardeners – who might have no idea the new plants were not pure T. virginiana.

Anderson despaired that, although his study of tradescantias had led to more accurate identification of wild species, the garden cultivars were still universally mislabelled as T. virginiana. Gardeners had no other option, because there was no correct name they could use to refer to these hybrids.

Tradescantia × andersoniana

Two years after Anderson’s book, botanists Ludwig and Rohweder (1954) tried to rectify the problem. They published the botanical hybrid name Tradescantia × andersoniana, in honour of Anderson himself. They referred to Anderson’s conclusions that cultivated plants are hybrids rather than pure T. virginiana, and decided that a single name would make it much easier to refer to those hybrids.

This would seem to be the end of the story, and over the next several decades gardeners gradually started using T. × andersoniana instead of T. virginiana to label garden cultivars.

But in fact, it wasn’t the end of the story. In a book on the taxonomy of cultivated plants, Walters et al. (1989, p. 31) pointed out that the name T. × andersoniana had never been described and was therefore invalid.

The rules for creating scientific plant names – like naming species and species hybrids – are very strict. Much stricter than the rules for naming cultivars! One of those rules is that, to name a new species or hybrid, there must be a precise botanical description of the plant in question. Ludiwg and Rohweder never described their hybrid, and none of the sources they referred to contained a description either. So T. × andersoniana is invalid, and can’t be used as a botanical name.

Tradescantia Andersoniana Group

For decades botanists had been pointing out that garden Tradescantia cultivars were labelled wrong, but never providing a valid alternative. Finally the Royal Horticultural Society (RHS) found a true horticultural solution – a cultivar group.

A cultivar is a type of plant that has been created or selected through human activity. Generally a cultivar belongs to a botanical species – for example, Tradescantia cerinthoides ‘Nanouk’ originates from the wild species Tradescantia cerinthoides. The name ‘Nanouk’ refers to a specific clone which people grow for its unique characteristics.

Sometimes, a cultivar belongs to a group of plants which doesn’t fit a particular botanical classification. This could be a subset of a single wild species which all share a particular trait, like a certain flower colour. Or it could be a collection of hybrids of known or unknown origin, which have certain characteristcs in common.

A cultivar group is the ideal was to classify these hardy garden Tradescantia cultivars. We don’t know for sure how they originated or what exactly their ancestors are. We do know that they don’t belong to any single particular species. We could label them all as just “Tradescantia” and be done with – but these plants clearly make up a defined group which is very different from, say, Tradescantia cerinthoides ‘Nanouk’! So instead, we place them in a cultivar group, which functions like a species, but for cultivated rather than wild plants.

According to the cultivar naming rules, we can repurpose the invalid name “andersoniana” for the newly-defined cultivar group (Brickell et al., 2016, Art. 21.6). So it becomes the Tradescantia Andersoniana Group. When referring to a specific cultivar, we can include the group name in brackets in place of a species – for example, Tradescantia (Andersoniana Group) ‘Osprey’.

The RHS started listing garden Tradescantia hybrids with the name Andersoniana Group in their 2000 Plant Finder (Royal Horticultural Society, 2000, p. 717). I haven’t found a hardcopy publication which officially establishes the group name with a description, so it will be established as part of the ICRA checklist (Brickell et al., 2016, Art. 27.1).

Although the group name has been in use for over twenty years, it still hasn’t been universally accepted. Part of the reason for that is that many sources didn’t recognise that the older T. × andersoniana name was invalid. Up until a few weeks ago, Plants of the World Online (POWO – a taxonomic database run by the world-leading Royal Botanic Gardens, Kew) listed the name as valid.

This threw me off for some time, because POWO is a very reliable source that I tend to defer to. But the RHS is another reliable source, and the two were in conflict! I did a lot of research to track down the original source of the T. × andersoniana name as well as the references from that publication, and check the botanical naming rules, to try and figure out what was going on.

Once I had come to the conclusion that the RHS interpretation was correct and the name must be invalid, I gathered my evidence and contacted the team behind POWO. And they responded very quickly, confirmed my findings and said they’d update the name. It’s now listed as “unplaced”, which means invalid. I’m proud to have made a small contribution to the accuracy of global taxonomy!

Hopefully the old name being correctly marked as invalid, along with the eventual published ICRA checklist, will help everyone to finally use the correct name for these plants: the Tradescantia Andersoniana Group.

References

Anderson, E. & Woodson, R. E. (1935). The species of Tradescantia indigenous to the United States. Contributions from the Arnold Arboretum of Harvard University, 9. doi:10.5962/bhl.title.153160. Biodiversity Heritage Library link.

Anderson, E. (1952). Plants, Man & Life. University of California Press.

Ludwig, W. & Rohweder, O. (1954). Zur Nomenklatur zweier Commelinaceen [On the nomenclature of two Commelinaceae]. Feddes repertorium specierum novarum regni vegetabilis, 56(3), 282. doi:10.1002/fedr.19540560304. Open access link.

Walters, S. M., Brady, A., Brickell, C. D., Cullen, J., Green, P. S., Lewis, J., Matthews, V. A., Webb, D. A., Yeo, P. F. & Alexander, J. C. M. (1989). The European Garden Flora: Volume II. Cambridge University Press.

Royal Horticultural Society. (2000). RHS Plant Finder 2000.

Brickell, C. D., Alexander, C., Cubey, J. J., David, J. C., Hoffman, M. H. A., Leslie, A. C., Malécot, V., Jin, X. (2016). International Code of Nomenclature for Cultivated PlantsPDF link.

Danielle

My acquisition of Tradescantia (Andersoniana Group) ‘Danielle’ is a story of co-operation and generosity between gardening enthusiasts. I am very grateful to Alasdair and Elizabeth MacGregor of the Elizabeth MacGregor Nursery in Ellenbank, near Kirkcudbright in Galloway, southwest Scotland, for their help in adding this rare and very special cultivar to the Collection.

Anemone ‘Wild Swan’

Elizabeth MacGregor is perhaps most famous for introducing Anemone ‘Wild Swan’ which she originally spotted in a batch of wild seedlings at her nursery in 2003 and which, after great encouragement from Roy Lancaster and years of trial and error with micro-propagation in order to bring it to market, was voted ‘Chelsea Plant of the Year’ in 2011.

Although I have never met, or even spoken to Elizabeth MacGregor, my email enquiry to the nursery in October 2021 was met with a very helpful response by her husband Alasdair who said that Elizabeth had promised to divide her plant in the spring and send me a piece. Would I please contact them again in early spring to remind them which I duly did, offering to pay for the plant and the p&p. Then it went quiet until, on 25th April, a box arrived with a perfectly packaged ‘Danielle’. No invoice, no request for any contribution to the cost of p&p. Just one plant enthusiast helping another.

What makes T. ‘Danielle’ so striking is the size of the flowers on compact foliage, the perfectly white petals, stamens and filament hairs topped with yellow anthers matched to lush mid-green leaves. For me, this is a better example than T. ‘Innocence’ whose flowers are smaller, grey/white by comparison and with mauve filaments. or T. ‘Blanca’ whose flowers seem to get lost in a mass of foliage.

Time will tell, and perhaps I am making an overly favourable judgement on a plant I am very pleased to have and have only just acquired, but so far it is up there with the best in my opinion.

My correspondence with Kevin Vaughn in Oregon revealed that he has produced a similar plant with very large pure white flowers which he is hoping to bring to market once trials have proved it is stable. I am looking forward to comparing it against ‘Danielle’.

Propagation

It is Saturday 26th March, the garden is full of Spring bulbs and blossom but, in a curious tradition only we could make up, the clocks go forward an hour tonight and British Summer Time (BST) begins! This means two things, it’s time to plant out Sweet Peas, and time to start propagating the Tradescantias.

By propagating, I really mean dividing or, more accurately, removing a slice from the outer part of the clump. This is the second year of the Collection and I am under an obligation from Plant Heritage to hold not only a main listed plant (an Accession), but also two others of each cultivar. This is known, as in Royal parlance, as an ‘heir and a spare’ (think Princes William & Harry!). It is an insurance policy to ensure the survival of each cultivar by always having a duplicate plant in case one perishes.

In this example, I am going to take a division of Tradescantia (Andersoniana Group) ‘Charlotte’ which is looking very happy, healthy and raring to go. The process I am using leaves 80% of the plant untouched and unharmed, thereby giving it the best possible chance of recovering quickly and growth unchecked.

A small outer section is selected and the hand trowel inserted smartly and vertically, ignoring the loud graunching noise as it cuts through the crown and thick fleshy roots. This can be a little disconcerting and it is only natural to think that irreparable harm is being done but, like other fleshy rooted perennials (Agapanthus, Rudbeckia, Sanguisorba etc.), the plant is programmed to accept the damage as part of life and recovers quickly.

The resulting division is lifted cleanly away from it’s parent and moved to the bench.

This one small piece could easily be divided into four or even six separate small plants, but I am just looking at two for my purposes. If I was propagating to increase stock for sale, as a nursery would, I would be pairing this division down into as many small individual plants as I could and would probably have taken a much larger division to start with, depending on the size of the clump.

Using an old breadknife, I cut the division into half, slicing clean through the roots and crown of the plant.

The mass of roots can clearly be seen in this picture but, remarkably, the plant will hardly notice and has enough growth material intact to carry on and produce new shoots and possibly even flower this year.

This size of division fits neatly into a 1 litre (12.5cm / 5″) pot with plenty of room for a season’s growth. Obviously, smaller divisions would only require a smaller (9cm / 3″ pot).

I pretty much use Melcourt SylvaGrow, peat free compost for all my propagation which includes seed sowing, cuttings, divisions and potting on. I have tried many, many alternatives but keep going back to Melcourt. I occasionally add a pelleted slow release fertilizer if the subject is likely to put on fast growth and requires additional long term nutrient, and sometimes add 20% John Innes or bagged topsoil if I think more ‘body’ is necessary, but I mainly use it straight out of the bag with excellent results.

I find the blend of fine bark, coir and wood fibre is good at retaining water and nutrients, is consistent and, importantly to me, contains no peat or recycled green waste. There is a similar Melcourt product with added John Innes but I find it more convenient (and less expensive!) to add my own in the ratio I want. There is enough base fertilizer to see the plant through the first 6-8 weeks, after which additional liquid feeds are required.

The compost is perfect for a job like this, clean and easily handled, needs not pressure, just tap the pot on the bench to settle the material around the roots, water, label and finish.

The parent plant is simply backfilled with soil and mulched to fill the gaping hole left by the division but in a week or two, the tremendous growth rate of the plant will completely mask the removal.

I will diarise a photo in 2, 4 and 8 weeks to demonstrate the recovery of the parent and growth of the divisions.

Hybrid Origins?

Tradescantia (Andersoniana Group) ‘Innocence’

I am sure this will be resolved over the coming weeks and months, but at the moment I am very confused about the origins and status of the Andersoniana Group hybrids. It seems pretty clear from all the research I have read that the parentage of most of the original hybrids were Tradescantia virginiana, Tradescantia ohiensis and Tradescantia subaspera. However, it is also true that Anderson himself found very few hybrids in the wild because although these three species share overlapping ranges, they enjoy differing habitats, therefore rarely coming into contact.

So, this led Anderson to speculate that it was only when two or more of these species were grown together in close proximity that hybrids began to appear through cross pollination. Tradescantia was certainly one of the first plants to be introduced into Europe from North America by John Tradescant the Younger in 1629, some 120 years before Carl Linnaeus even named the plant Tradescantia virginiana in Species Plantarum in 1753, certainly long enough for multiple hybrids to appear in domestic and botanic gardens in the UK and on the continent of Europe. However, Anderson then went further and showed through gene and cell research that these hybrids also crossed back with one or more of their parents creating ‘interspecific hybrids’.

Over the last 200 years, hybrids worthy of cultivation have been selected, propagated vegetatively, and, until recently, were known by the name Tradescantia × andersoniana. Further deliberate crossing and back-crossing has subsequently produced huge variations in flower colour and size, leaf colour and form, height, vigour and flowering period. Of course, naturally occurring hybrids are still being discovered and selected, and I think it is probably true to say that what we now call Tradescantia Andersoniana Group is a mixture of both.

Tradescantia virginiana ‘Brevicaulis’

I am indebted to Jorge of blog.primrose.co.uk
for the following detail which explains the origins and
differences between Species, Variety and Cultivar.

What is a species? One definition states a species is a group of
similar individuals which can
reproduce successfully with each other
while at the same time being reproductively isolated from other similar
species. This definition leaves it up to scientists to decide when a group of
individuals is distinct with some placing greater weight on genetics, others
more obvious characteristics such as their morphology.

When a group of individuals becomes geographically isolated, it will
begin to develop unique traits, making it distinct from the rest of the
species. These distinct groups are known as varieties. Over time, they may
become so different from the parent group that they are unable to breed,
leading to the creation of a new species. Often, however, a variety comes into
contact with its
parent group, resulting in an influx of genes that
erodes their distinct features, reintegrating it into the greater species
group.

Varieties are true to type as their seeds produce offspring with the
same unique characteristics of the parent plant. Cultivars are distinct from
varieties in that they do not occur naturally in the wild. Cultivars are selected
by humans for specific characteristics and are propagated through vegetative
cuttings i.e. cloning. Propagation by seed will often lead to something
different from the parent plant and as such they aren’t true to type”.

Synonyms

Tradescantia (Andersoniana Group) ‘Carmine Glow’ or ‘Karminglut’?

Synonyms are a really BIG problem for gardeners in general and National Collection Holders in particular. When a plant becomes popular and sales increase, it usually isn’t long before a commercial plant nursery offers an extremely similar plant for sale under a different name. There might be a tiny difference in flower or leaf colour or no difference at all! They want more sales and if people are buying a particular plant they will also buy ones which are very similar, thinking they are getting something new and different. Collection Holders like myself might hunt down a plant with a name they don’t recognise only to find it is something else they already have but under a different name. This is very frustrating and can be time consuming and sometimes expensive. I would normally advise people only to buy from reputable sources but they are often the biggest culprits!

It seems to me that because Tradescantias are so promiscuous, and produce cross pollinated seedlings at the drop of a hat, this is why there are so many different hybrids, many of which are only subtly different to each other. On any given plant, not all the flowers will be identical, so are the two flowers featured above from the same plant or differently named plants? They are accepted by the RHS as different plants, ‘Pauline’ and ‘Pink Chablis’, but at several points last year both plants looked identical. The flowers seem to have stronger or weaker flower colours depending if they are grown in sunny or partly shaded positions, and colours seem to weaken as the flowering period comes to an end. Of course, there are many other differences and variations which characterise specific plants, not just flower colour, but these are often very subtle indeed!

A former Tradescantia National Collection Holder, Hazel Kaye, recently told me that she purchased a Tradescantia Andersoniana Group plant named ‘Bridesmaid’ at a plant sale in Leicester and believed she may have found something new. It turned out to be a self sown seedling from a local garden which the owner had named herself and which had not been trialled or tested before offering it for sale. It was a poor selection and not worth pursuing.

Tradescantia ozarkana – a species widely distributed in Missouri, Arkansas, and Oklahoma, USA

I am indebted to the Botany Advisory Services of the RHS who kindly allowed me to quote from their leaflet ‘Guide to Plant Names‘.

“Although the ideal is for each species or cultivar to have only one name, anyone dealing with plants soon comes across a situation where one plant has received two or more names, or two plants have received the same name. In each case, only one name and application, for reasons of precision and stability, can be regarded as correct. Additional names are known as synonyms.

In the past, and in the nineteenth century in particular, when a huge amount of botanical exploration was taking place, it was possible for botanists to be beavering away describing and naming plants in different parts of the world, blissfully unaware that they were duplicating someone else’s work. This is perhaps difficult to understand in these days of instant global communication, but it led to many cases of a single species with two or more names, or two or more species with the same name. The simplest way to resolve the problem of duplicated and superfluous names is to invoke a rule of priority – the earliest name correctly published wins and new names are therefore needed for some plants with later, incorrect names.

This is a basically sound idea but has led to changes of some very familiar, yet incorrect names due to the discovery of earlier, correct ones in very obscure texts. This can have a destabilising effect, contrary to the intention of the rule of priority, so there is now a much more pragmatic view being taken, with some of the more destabilising proposed name changes vetted by an international panel and often rejected if the technically wrong name is widely known. For example, the popular heather, Erica carnea, was saved in this way from being changed to Erica herbacea.

Cultivars acquire extra names in similar ways to wild plants and also through the deliberate re-naming when the original name is felt not to promote good sales! The same principle of priority applies for cultivars as for wild plants so there are always cases where correction is needed. However, it is not always appropriate to provide a new, unique name for a cultivar which has been given the same name as an existing plant. Where there are large groups of cultivars, such as in the genera Fuchsia and Pelargonium, repetition of cultivar names has proved difficult to avoid. In these cases, names can be qualified with the name of the breeder, the date of introduction or the plant type to help pinpoint their identity.

In the case of wild plants, correct identification and naming relies on knowing what species exist and how they are related. Add to this the increasingly reliable evidence of evolutionary trends provided by DNA and molecular studies and the fact that, for better or worse, the naming system aims to reflect the classification and therefore relationships, and it can be seen that some changes are inevitable….genera being split, new ones created, others amalgamated.”

This is a major source of irritation for National Plant Collection Holders as I have already said. In the main picture above, Tradescantia (Andersoniana Group) ‘Carmine Glow’ is the same plant as ‘Karminglut’ (which means Carmine Glow in German) and is recorded as such on the RHS database. However, I have discovered sellers who offer both as distinctive plants.

Likewise, Tradescantia (Andersoniana Group) ‘Sweet Kate’ (above) is a popular variety for sale in the UK due to it’s distinctive yellow foliage and mauve flowers. However, in the United States, I have discovered a virtually identical variety for sale on the internet called ‘Charlotte’s Web’. It remains to be seen if this is indeed the same plant but the images I have observed would suggest so.

As my Tradescantia journey progresses, I will no doubt be discovering many more instances of the same cultivar with different names and my collection will require constant scrutiny to weed out the synonyms.

Welcome!

Welcome to this website all about Tradescantia virginiana and the Tradescantia Andersoniana Group.

I hope you find the information I provide useful, the photographs inspirational, and the journey interesting. As the newly accredited National Plant Collection Holder, I am on a mission to collect all known cultivars of hardy Tradescantia listed in the RHS Plant Finder over the last 20 years or so, many of which are no longer cultivated by plant nurseries and may prove difficult to find. However, they may still be available from small independent nurseries who do not list plants in Plant Finder, or fellow gardeners who bought plants many years ago and may not realise those particular cultivars are now threatened and could be lost forever.

As well as playing my part in helping to preserve the plants for future generations to enjoy, I will also revel in the detective work, the research and the joy of sharing all this with other interested gardeners. I hope you enjoy it too.

David Simpson