Mexican bluebell or wild petunia (Ruellia tweediana Grisebach) is a member of the Acanthaceae native to Mexico. It has been known under the name Ruellia brittoniana since 1941, but it was discovered that August Heinrich Rudolf Grisebach had already named the plant in 1879. Mexican wild petunia is passed off to the unwitting public as a 'butterfly plant--caveat emptor!

The wild type or natural Ruellia tweediana [rue ell' ee ah tweed' ee ana] grows to about a meter in height and has blue flowers. Under cultivation, the plant has produced standard and dwarf cultivars (cultivated varieties) with white, pink, red, or blue flowers. The cultivar characteristics remain if the plant is propagated from the subterranean rhizome or runner.

But if allowed to propagate from seed, the seedlings tend to revert to the wild tall, blue-flowered type. Since the plant readily produces seed, it is almost impossible not to end up with the scraggly wild type all over the garden. ("Mexican Bluebell (Ruellia tweediana Griseb.): A Pretty Invasive Weed", Roger L. Hammer, Wildland Weeds, Vol.5, No.2, Publication of Florida EPPC, Spring 2002)

I have never planted Ruellia tweediana in my garden. They are there because the runners have come over from a neighbor's yard. Although I've pulled them repeatedly and even sprayed with glyphosate, the plants are now a good twenty feet into my garden and defy all attempts to eradicate them. About half the plants have reverted to the blue. It is no wonder Mexican wild petunias are described as a Category I Exotic Pest Plant. I have my own descriptors....

As far as being 'butterfly plants', I have never seen any butterfly stop to nectar at the flowers. Nor have I found any kind of caterpillar eating the plants. Heck, I've never found any thing eating these plants! Mexican wild petunias are like cheap plastic flowers that reproduce like rats. They are beyond useless for attracting butterflies since they choke-out all other desirable plants like milkweeds, ironweeds, and Lantana.

It really is a shame the flowers are so attractive to humans and that's the caveat--you like them now. But if your soil doesn't freeze hard, you are not going to like them next year.