The Tovara Problem

The genus Persicaria contains some of the most incredible herbaceous plants for foliage effect. From the very popular P. microcephala ‘Red Dragon’ to the increasingly popular P. runcinata ‘Yunnan Giant’ (syn. ‘Green Fantasy’), Persicarias are a staple of the ‘hardy exotics’ movement in the UK, although they’re also found in many other garden styles too. The most refined of the genus are those species found in Section Tovara.

Persicaria virginiana

Persicaria virginiana is a well known species from the United States. It was first named as “Polygonum virginianum” by Linnaeus in 1753 (fair to assume it was known in botany, if not cultivation, at that point) and has since become a deservedly popular addition to temperate gardens in Europe. As European explorers travelled more extensively in Asia they started to find other Persicarias that were similar yet also different to P. virginiana. In what could be interpreted as ‘taxonomic laziness’ a new group was created and all material, American and Asian, was placed into ‘Persicaria virginiana var. filiformis’. It’s entirely possible that taxonomists looked at the material and realised that separating them and naming new species would be complicated, although not lumping them straight into P. virginiana suggests there was a case to be made that they were different.

Persicaria virginiana in flower (late summer)

The recent taxonomic approach to this area of Polygonaceae (splitting ‘Persicaria’ into Bistorta, Koenigia and Persicaria) found there is sufficient genetic evidence to conclude that ‘Persicaria virginiana var. filiformis’ is an invalid name, and that P. virginiana represents the American species and P. filiformis represents the Asian material. The same study also concluded that there was a second Asian species, P. filiformis, within this section of Persicaria; this is currently debated, so for the purpose of this work I am going to stick to there being two species of Persicaria within Section Tovara. It’s worth noting at this point that there are plants currently labelled as ‘Persicaria tovara’; this is an invalid name and has likely come about as a result of confusion between the ‘genus’ and ‘section’ (maybe there was a plant somewhere labelled ‘Persicaria Section Tovara’ at some point?).

Persicaria virginiana represents the greatest bulk of material in cultivation at this time, both in terms of cultivars and the physical number of plants growing in gardens. Although I’ve seen it growing happily enough in full sun I do think it looks happier in a little shade. The appeal of this species is its fresh green leaves with their distinctive dark chevron markings, although the whispy sprays of red flowers above (described rather meanly by the late Beth Chatto as “rat tails”) and the autumn tints are also attractive.

This species is widely known for its self-seeding, and periodically a seedling will show up with a slightly different trait. I’ve not seen any ‘bad’ cultivars, although I’m not completely sure that all are necessarily distinctive. Clones raised from seed are usually largely true to their parent, but great care should be taken to ensure that the progeny match the parent plant(s) before they’re sold or traded under that name. With the non-variegated cultivars I think it’s probably the case that most gardeners will choose to grow one cultivar, although there are some who will inevitably enjoy collecting different clones.

Persicaria virginiana ‘Painter’s Palette’ at East Lambrook Manor (late summer)

To the best of my knowledge there are two variegated cultivars of P. virginiana, P. virginiana ‘Variegata’ and P. virginiana ‘Painter’s Palette’. I’ve not yet been able to pin down a precise origin for P. virginiana ‘Variegata’, but I suspect that it was in cultivation in the late 19th century. It has a reputation for being not entirely hardy, but at this time I suspect this might not be entirely true. The foliage is brightly marbled white. This, and ‘Painter’s Palette’, are very bold and distinctive foliage plants that might not be to everyone’s taste, but can be used effectively in partially shaded planting schemes.

Persicaria virginiana ‘Painter’s Palette’ in a woodland garden (early summer)

P. virginiana ‘Painter’s Palette’ is likely to be derived from P. virginiana ‘Variegata’, and differs in its bolder splashes of variegation and, crucially, the presence of a bold chevron marking on each leaf. This cultivar has been attributed to the late plantsman Eric Smith. Some time between 1965 and his death in 1986, likely to be around 1975, it’s believed that Smith raised a seedling from P. virginiana ‘Variegata’ which had a more robust constitution and the brown chevron marking on the leaf. The variegation is usually light golden yellow in spring and early summer but it can fade to white during the late summer and autumn. Flowers are red and are of no real consequence. P. virginiana ‘Painter’s Pallette’ is fairly widely grown today and is usually raised from seed; seedlings are quite variable so it’s worth looking for a good clone. One of the biggest challenges hunting the origins of Persicarias is that people tend not to make a big fuss when they raise something new. It’s only recently that the genus has had any meaningful scrutiny, and new selections and cultivars have slipped in and out of cultivation largely unknown. Of course many plantspeople do keep notebooks, but Eric Smith wasn’t one of them; while P. virginiana ‘Painter’s Pallette’ is usually attributed to Eric Smith, at this time we can’t be 100% sure that he raised it.

Persicaria virginiana ‘Painter’s Palette’ (mid summer): note the slightly yellow tint to the variegation,
as opposed to the whiter variegation of the plant photographed later in the year at East Lambrook

P. virginiana ‘Alba’ is a bit of an oddball clone. The white flowers manage somehow to be even less significant than those of P. virginiana, and the foliage and stems are notably a paler green. Crucially the chevron markings are nearly invisible on this selection. I consider P. virginiana ‘Ballet’ to be a synonym of P. virginiana ‘Alba’, and am yet to see any evidence against this assumption.

Other cultivars of P. virginiana include ‘Batwings’ (chevron markings flare out away from the midrib of each leaf, plus a more compact habit) and ‘Lance Corporal’ (best described as the markings being solid and a deeper V-shape). Both of these cultivars have been selected for their somewhat different markings, although neither are vastly different to the species itself.

There are three cultivars notably absent from this text so far: ‘Brush Strokes’, ‘Compton’s Red’ and ‘Guizhou Bronze’. Two of these are of known Asian origin, with the third highly likely, I believe, to be of Asian origin. Assuming that pending clarification on the status of P. neofiliformis we call Asian members of Section Tovara ‘P. filiformis’, these three cultivars represent P. filiformis in cultivation. If I was going to take a massive speculative leap and choose one of the three that could, potentially, represent P. neofiliformis in cultivation I would choose P. ‘Brush Strokes’ based on its noticeably broader leaves and slightly ‘felty’ texture, but this is just conjecture on my part.

Persicaria filiformis ‘Brush Strokes’

P. ‘Brush Strokes’ (syn. ‘Brushstrokes’) was originally spotted growing in a garden in Tasmania by the legendary American plantsman Dan Heims. This fine plant, possibly the most magnificent plant in Section Tovara in cultivation, was launched by Terra Nova Nurseries. Early in the year this plant is nothing special, but as the growing season progresses the leaves expand outwards and as it does so the chevron marking becomes ‘stretched’, and rather than being block of colour it looks like each leaf has been painted with delicate brush strokes, hence the name.

Persicaria virginiana ‘Compton’s Red’ flowering in November at RHS Wisley

P. ‘Compton’s Red’ CDR549 (syn. ‘Compton’s Form’) is the best established of these three clones in cultivation. It was collected in 1989, having been spotted on a roadside bank some 30km south east of Baoxing in Sichuan Province, China. This form is very distinctive, with its multicoloured ‘metallic’ leaves an instant draw for gardeners. As a massed planting under trees it’s spectacular, giving superb foliage effect right from its emergence in spring until its dying back in the autumn.

P. ‘Guizhou Bronze’ PAB9127 is less well known than the two above. It’s a quietly charming plant, a little plain and ordinary early in the year but by autumn it takes on a very pleasant bronze sheen to its leaves. It was collected by Nick Macer and Paul Barney in 2011 in Guizhou Province, China.

Persicaria filiformis ‘Guizhou Bronze’

Genetic study of plants has revolutionised botany but does leave us with an obvious question: how do non-botanists tell species apart? In the case of the Persicarias of Section Tovara I suggest the following (assuming the plants are grown in temperate climates):

Persicaria virginiana and its cultivars flower earlier in the season, usually during late summer, often seeding around after it has done so.

Persicaria filiformis and its cultivars flower much later in the year, often well into autumn (a month or more after P. virginiana, assuming the plants flower at all), and as such seedlings are exceptionally rare (usually only if plants are growing in artificial conditions).

I appreciate that this will be regarded by some as ‘lazy botany’ but if we’re going to have taxonomic revisions then it’s important to have a straightforward interpretation that can be used widely. Differences in foliage could also work (leaves of P. filiformis are usually larger than those of P. virginiana) but in a genus notorious for its variability and for changes of physiology according to growing conditions to align species solely on their foliage could, in more extreme cases, cause confusion.

A few notes on cultivation…

All Persicarias in Section Tovara require very similar growing conditions to be at their best. In hotter and drier gardens they should be grown in cooler, shadier conditions, while in cooler and damper gardens they are tolerant of more sunshine (although in exceptional years they may suffer if they do get too hot and/or dry). These plants dislike being too dry or exceptionally wet, so a free-draining but humus-rich soil is perfect. These plants can also be grown in containers to great effect, providing the container is cool and shaded; they are no more or less susceptible to vine weevil grubs than most other plants.

It’s very important not to cut down the woody stems of these Persicaria during the autumn or winter. It seems that they’re prone to dying during winter if stems are removed (stems can be shortened to no less than 15cm/6” if absolutely necessary); it’s best to remove old growth as new growth gets underway in spring. It’s possible that the reputation of some clones not being hardy might be due to the effects of having their stems removed rather than the effects of cold.

The Persicarias in Section Tovara are particularly susceptible to being buried, so take care not to plant them too deeply and ensure that mulches, where applied, do not bury the growing points. If there is a need to apply a mulch (for example in areas with exceptionally cold winters) a dry mulch such as straw or the fronds of ferns will be considerably better than using a wet mulch (compost, manure etc). Remove the mulch when conditions allow so the plant can come back into growth.