My plan is to add to this post when I come across a new name for a well known plant, so once the ball is rolling the newest name changes should be at the top.
“Why must all these plant names change?” the gardeners ask. I have no intention of discussing ‘why’ in any meaningful sense in this post, only to focus on specific examples in the hope that they might help more committed gardeners keep up to date.
Persicaria > Bistorta, Koenigia and Persicaria
This is something I’ve been studying in great detail and I will devote whole pages to the three genera when I get around to it, plus likely a page to describe the changes in more detail. Might even do a ‘hyperlink’ to each if I learn how…
The history of this part of the Polygonaceae has been nothing if not convoluted. Thankfully research into the genetic makeup of these plants has proven some long-held theories about how these plants fit together to be true. But here, in summary, is how the split settles out….
Those plants formerly in Persicaria that have the main bulk of their foliage at the base, either as a mat of leaves from creeping shoots or emerging as a mound of foliage, with flowers held clear above, now belong in the genus Bistorta. We now have Bistorta affinis, Bistorta amplexicaulis, Bistorta vaccinifolium etc. A couple of species have changed, with ‘Persicaria bistorta’ becoming Bistorta officinalis (which has two cultivars, ‘Superba’ and ‘Hohe Tatra’), and what used to be ‘Persicaria bistorta ‘Carnea’ is now Bistorta carnea.
The ‘Persicarias’ that emerge from woody roots belong to the genus Koenigia. This genus includes K. campanulatum in its various cultivars, the real K. alpina, and the large plants seen as ‘Persicaria alpina/polymorpha’ which are in fact Koenigia x fennica.
The remaining plants, many of which have the classic chevron markings on the foliage and also have stems that zig-zag (to varying degrees) remain Persicaria, so Persicaria microcephala ‘Red Dragon’ etc. There’s been a splitting of Persicaria virginiana var filiformis into two, possibly three, species; Persicaria virginiana (USA), Persicaria filiformis (Asia) and possibly Persicaria neofiliformis (Asia). I think most plants of this section of Persicaria, ‘Lance Corporal’, ‘Batwings’, ‘Ballet’/var. alba’ etc, belong to the American P. virginiana, while ‘Compton’s Red’ and ‘Guizhou Bronze’ are definitely Chinese in origin and will belong to either P. filiformis or P. neofiliformis. At this moment I have no idea which, and I’ve deferred this question to a higher botanical power!
Aster > Symphyotrichum, Eurybia, Doellingeria, Aster
As it stood, the genus ‘Aster’ used to be an enormous collection of ‘daisy’ species spread around the world (although mainly in the Northern Hemisphere). It was convenient to have them all lumped under one genus, although some were originally named under other genera beforehand. While the mega-genus was convenient for gardeners it wasn’t accurate, so a revision has been made. Those ‘asters’ that have leaves that clasp their stems (grab your wrist with your other hand, the hand being the base of the leaf and your wrist representing the stem) have moved into Symphyotrichum; those who get irritated by having to learn a new name won’t like the fact that that majority of garden asters now belong in this genus. The North American ‘wood asters’ with their main mass of leaves at the base of the plant and then flowers on long stems (which have a few smaller leaves on them) belong to Eurybia; the best known in this genus is Eurybia divaricatus, although E. schreberi and E. x herveyi are worth growing too. The tall and infrequently grown “aster umbellatus” is now Doellingeria umbellata; this species has tall straight stems with flat heads of white flowers and, crucially, grows from rhizomes rather than more conventional roots. The genus Aster still exists but is now used for European and Chinese species whose leaves are borne all along the stems, such as Aster x frikartii and the very rarely seen evergreen shrub Aster albescens.
Sorbus > Sorbus and Aria
This is a new one on me and I’m hoping that I will gain clarity over the next few weeks. When you look across the genus ‘Sorbus’ it’s fairly clear that there is something that doesn’t quite fit. There are lots of the easy to recognise species with pinnate leaves and small fleshy fruits (think Sorbus aucuparia), but then there are trees like ‘Sorbus aria’ which have simple leaves (leaf-shaped leaves!) and quite different fruits. There is it seems sufficient difference for the two groups to be split up; those with pinnate leaves stay in Sorbus while those without (and with different fruits) move into Aria. (Does this mean that ‘Sorbus aria’ is now ‘Aria aria’?!). This is a new change, to me anyway, so this part of this post might well change once I get my head around it!
will now become Aria megalocarpa.
Azaleas > Rhododendrons
This one makes a lot of sense really, after all they’re clearly plants with a lot in common. Genetic research in recent years has firmly put the azaleas into the larger genus Rhododendron, but also threw up something rather interesting; evergreen and deciduous azaleas aren’t all that closely related to each other! Any plant labelled ‘Azalea X’ is in fact ‘Rhododendron X’. Other minor genera around Rhododendrons have also been put into Rhododendron, namely Ledum and Menziesia.
Dicentra > Lamprocapnos, Dactylicapnos, Dicentra*
This change has caused a lot of irritation in gardeners, partly because the formerly ‘Dicentra spectabilis’ is a popular garden plant and gardeners like to resist change, but also because the names assigned are seen as being ‘too difficult’ for normal gardeners to understand. I suspect the latter is probably part of resisting change too, to be honest.
The genus used to be ‘Dicentra’ based on the flowers being the same shape, but now the genus is split. Dicentras grow from a rosette of leaves and have no foliage on their flower stem (the stem is bare from the ground right up to the flowers), while Lamprocapnos contains one species (L. spectabilis) that has leaves on its flowering stem, and all of the yellow flowered climbing species belong in Dactylicapnos.
*I think I’m right in saying these names were the original names used when the plants were discovered.
Lamprocapnos spectabilis ‘Valentine’ 
Lamprocapnos spectabilis ‘Alba’
Michelia > Magnolia
Nice and easy this one; the main difference between Michelia and Magnolia was that the Michelias bore their flowers along their branches while Magnolias bore theirs at their branch tips. Research places the Michelias into Magnolia. This hasn’t created much friction in horticultural circles, but the ‘Michelias’ aren’t particularly hardy and need a little more care, so tend to be grown by more knowledgeable gardeners.
All of my pictures of what were formerly Michelias were lost when my old external hard drive failed. Must make a point of photographing some more this year!
Schizostylis > Hesperantha
The genus Hesperantha has been around in specialist bulb collections for a while, and is really very similar to what we used to call ‘Schizostylis’. In fact the only major difference between them was that ‘Schizostylis’ grows from a short rhizome while Hesperanthas grow from corms. DNA evidence put them firmly together, so ‘Schizostylis coccinea’ is now an autumn flowering, hardy and more moisture tolerant species of Hesperantha, Hesperantha coccinea.
While we’re on the subject of name changes, let’s look at the common name for H. coccinea, ‘Kaffir Lily’. If you go to South Africa and call someone a ‘Kaffir’ they will likely punch you in the face; ‘Kaffir’ is an offensive term for black South African! Nonetheless the common name ‘Kaffir Lily’ is still widely used in the UK, but in a society where the nursery rhyme ‘Baa baa black sheep’ has been banned in some nursery schools because it’s considered racist (despite little to no historical evidence) we should probably be aware that the word could feasibly cause genuine offence. ‘Cape Lily’ or ‘Scarlet River Lily’ could be better alternatives.
