Since no one's jumped in yet, I'll give this a whirl.

Are you certain that the verbena sold to you is indeed Homestead Purple, or could it have been mislabeled? Have you contacted your supplier to find out more about this? Perhaps other plants marked HP have bloomed in the same manner.

Verbena can be propagated by cuttings or seeds. Cuttings will be identical to the mother plant, but seeds can be variable, especially if other varieties of verbena are growing nearby which may have cross pollinated, but even pollinated by the identical variety. A lone specimen of white Phlox paniculata David set seed here (so self-fertile) & one of the seedlings bloomed lavender. Checking to see if this was unusual, found David's Lavender, a sport of David introduced & patented by Itsaul Plants in Georgia. Assuming theirs originated in the same way as mine and has been continued from cuttings of the seedling (vegetative propagation), but it's possible the Lavender grew from a branch of David.

The link is to some varieties new for 2014. There's a slideshow & Lanai Twister Purple looks something like you describe. There may be others.

A sport usually arises as a branch different in growth on an existing plant & is considered a mutation. If cuttings from the oddball branch grow identically, and cuttings from those plants down the line, it's considered a stable mutation & can be considered a new variety. Sometimes a stable mutation will revert & show the characteristics of the plant from which the sport arose. That's all memory turns up on the subject, but others likely know more.

If you determine yours is a new variation, you could always fool around with cuttings to be sure it's stable. Don't know anything about patenting plants or selling distribution rights to such plants.

Rosie, how exciting to have met Dr. Armitage & how lucky to get a special plant before its official introduction!

Here is a link that might be useful: Verbena new for 2014

Sue,

Thanks much for info/clarification, et al. Right now flowering is slowing on all the Homesteads so I will have to update later.

Don't know about mislabeling. These were grown for my SIL who owns a landscaping company.

Interesting about the P. paniculata. And what a coincidence. I gave Bobby Saul some of the Homestead Purple when Dr. Armitage gave it to me. The rest is history.

My daughter got her degree in Horticulture at UGA and I spent many, many days going to lectures by Alan and Dr. Mike Dirr. They gave me so many great plants and the memories will always be with me. What a pair those two best friends were!!

I'll be back with more when reblooming resumes and I can get a pic.

Rosie