This topic is dedicated to those long persistent misnomers that seem near impossible to correct. I start with one that I have personally worked on for the last 30 years or more.
There is an Allium widely distributed as Allium tanguticum (from China), a real species, but everything sold under this name (and I mean EVERYTHING) is Allium senescens ssp. montanum. There is a long story to this misnomer, but for the time being I'll skip the long story and jump to the crux of the problem.
Allium tanguticum is not in cultivation! Yet, many nurseries selling Allium plants sell something labeled as Allium tanguticum. Allium tanguticum is a bulbous species (not rhizomatous) with leaves 1-3 mm (quite narrow), and purplish flowers. The requisite imposter is always the same thing, a poor pallid form of Allium senescens ssp. montanum, with strong Iris-like rhizomes and twisting shiny green leaves about 1 cm wide. Not sure why such an obvious misnomer is so persistent, but it is, perhaps perpetuated by the fact large bulb companies such as McClure and Zimmerman persist in such sales and refuse to listen to any correction.
This spring (2013), I notified Arrowhead Alpines that their Allium tanguticum was the familiar misnomer, that the true plant was not in cultivation. Rather than accept my evidence and expertise in the genus, they offered to send me a plant of Allium "tanguticum" along with some Epimedium plants I had ordered. Upon receipt, I could see that once again (how many times must I witness the same mistake) the plant was Allium senescens ssp. montanum. It had a horizontal rhizome (not tanguticum) and 1 cm wide leaves that spiralled (not tanguticum). I have informed them again of my ID, but thus far no response, they still sell it as Allium tanguticum.
It started to flower. Now here's the funny thing, the form of Allium senescens ssp. montanum which goes around as A. tanguticum is inferior, an insipid pale lavender thing with miserable blooms on 2' stems. There are some really excellent forms of Allium senescens ssp. montanum with floriferous heads of deep pink, but with the tanguticum-imposter, the plant form and flowers are worthy of the dust bin. Good thing Arrowhead Alpines doesn't have a photo of their misnomer, I don't think a picture would help sell it. Heck, it's only $8, mine just went into the compost pile.
McClure and Zimmerman even sell a selection of Allium tanguticum, one called 'Summer Beauty'. Definitely an improvement, not as insipid and ugly as the imposter of the base species, but still an imposter nonetheless (looks like an Allium senescens x nutans type hybrid). I have tried these too, just to verify their lack of validity, bingo!
The imposter, a lousy form Allium senescens ssp. montanum sold as Allium tanguticum by Arrowhead Alpines: