“The smartness and absurdity of plant names” is one of things I’m going to be discussing here on the re-launched Grahams Garden blog, as I did on its predecessor Transatlantic Gardener. We can start with an old favourite given heightened absurdity by the good people at the Royal Horticultural Society – Digiplexis.

“Oh, no!” I hear you cry… Yes, I’m sorry. And we’re going to do Mangave as well…

So. Here’s the story.

Our British native foxglove, a familiar tough biennial, is Digitalis purpurea (above left). The Canary Island foxglove is Digitalis canariensis (above right), a tender rather woody perennial. Charles Valin, then plant breeder at Thompson & Morgan, crossed the two species together and gave the resulting plant the name of Illumination Pink (above, centre). It won the Chelsea Flower Show Plant Of The Year award in 2012.

But, before the Canary Island foxglove was Digitalis canariensis, it had been Isoplexis canariensis – botanists had thought it was sufficiently different from other foxgloves to be in a genus all of its own. Closer examination proved that this was a mistake and the fact that it crossed easily with D. purpurea was one of the reasons that it was re-classified as a Digitalis. The RHS botanists gave the new hybrid the botanical name of D. x valinii, commemorating the breeder who first made the cross.

Other breeders then got in on the act and made their own crosses. And, somewhere along the way, over in the United States, someone decided that crossing two different genera together – Digitalis and Isoplexis – sounded much more impressive than crossing together two different Digitalis and the name Digiplexis® was born. This was much more a marketing exercise than it was a piece of thoughtful botanical nomenclature.

So, let’s be clear. Digiplexis® is an invalid, made up name with no standing whatsoever and which only serves to confuse gardeners. So it was especially maddening to see, just the other day, in the new plant centre at the RHS Garden at Wisley in Surrey, plants labelled Digiplexis® (below). And note the little symbol for a Registered Trade mark. This is a marketing exercise, not a plant name. Aren’t plant names confusing enough, without this sort of nonsense - and without one branch of the RHS muddling up the good sense of another?

But wait, there’s more. Pretty much the same thing has happened with Mangave®. Note that little ® again. This time we’re talking about rosette-forming succulents mainly from arid regions of the Americas – Manfreda and Agave. Nearly twenty years ago it was recognised that there was no justification for keeping these two genera separate so Manfreda was merged into Agave. All very sensible.

But then in the same way as with those foxgloves someone realised that, from a marketing point of view, crossing plants from two different genera was much more impressive than crossing two different species of the same genus. And Mangave® was born, recommended for patio planters.

But there’s payback for this sleight of hand. That first Digitalis hybrid turned out to be far less hardy than was originally announced and so the name Digiplexis® has become attached to plants that fail to make it through their first winter. Something similar will probably happen with Mangave®, which in the UK need grittier compost and more winter protection than is often mentioned.

But haven’t we suffered enough? In recent years plant taxonomists have taken on board the idea that they exercise caution in their decisions about plant names and respect the needs of the wider plant community. The shoot-in-foot madness of trying to make us call chrysanthemums Dendranthema is long gone.

But then someone else comes along and confuses everyone all over again. And the very least that the RHS can do is make sure that it agrees with itself.