One of our long-time favorite summer perennials is the amazing Lychnis ‘Orange Sherbet’. This gem first came into our life when I traveled for a Midwest talk in 2004, where one of the hosts asked if I’d like a plant of her Lychnis coronata. I assumed she was talking about either the common, short-lived Lychnis coronaria or Lychnis cognata, both of which were not of interest. She explained that the amazing perennial, Lychnis coronata, was often confused with the other two, and consequently was virtually unknown, other than as a Midwest pass-along plant. I returned home with a small start, and it didn’t take long to become one of the stars in our garden.
As we explored deeper, we found that Lychnis coronata is actually a synonym for Silene banksiana, which isn’t the same plant. Neither is the plant Lychnis cognata, which we subsequently acquired from China for comparison. We still list it under the acquired named, but since it’s almost completely sterile, we’ve concluded that it’s most likely and old hybrid, possibly between Lychnis cognata and Lychnis coronaria.
Regardless of the taxonomy, ‘Orange Sherbet’ is hard to beat as a garden perennial. For us, it explodes out of the ground in spring, forming a 2′ tall x 3′ wide tight clump with the first flowers appearing in mid-May, and continuing virtually all summer. It performs best in very light, open shade or in a couple of hours of sun. Since we have so few orange-flowered perennials, this is a welcome addition to the garden designers palette. Hardiness Zone 5a-9b, at least.

Could part of its parentage include sieboldii? Issima has a double flowering form (Lychnis sieboldii ‘Flore Plena’), another orange to the garden design palette.
It’s certainly possible