Mexican petunia, Ruellia tweediana, is one of those infrequently occurring, brilliant blue flowering herbaceous shrubs that is abundantly used. Unfortunately, it is on the Florida Exotic Pest Plant Council (FEPPC) list as a Category 1, which is defined as, "Invasive exotics that are altering native plant communities by displacing native species, changing community structures or ecological functions or hybridizing with natives." See: www.fleppc.org

However, it is not on the Florida Department of Environmental Protection prohibited plants list nor is it on the FDACS nor the USDA noxious weed list.

I'm not sure if it belongs on the FEPPC list. I haven't seen my healthy stand set seed. Nor have I been able to find obvious flushes of sprouting seedlings. According to botanist Richard Wunderlin of the USF, the fruits are relatively small and contain only a few seeds and so may not be noticed. When mature, the seed pod splits open and shoots the seeds some distance away from the plant.

The three little plants I set out were fine for about two years. Then the stems had elongated to four feet and started flopping over and starting new plants at the nodes. It created quite a tangled jungle that spread out of bounds — about five times more than my "plan" had called for.

To keep them in bounds, they need to be whacked back two times a year, which they seemed to thrive on. The pruning creates a pile of yard waste, which most people don't compost, and the yard workers haul it off to the landfill, which doesn't need any more debris.

I started using Roundup herbicide and I think they like that, too. This will come down to, as with many of the other cute little plants, a hands-and-knees grubbing operation to remove the tangle in my backyard border.

According to Dr. Rick Schoellhorn, floriculture researcher at the University of Florida, Mexican petunia, Ruellia tweediana ( R. brittoniana ) is actually a whole group of nearly identical species/forms.

Schoelhorn reports that there are supposedly some sterile Ruellia, but no named cultivars except the dwarf series called "Katie" (blue, white, pink, and variegated). He says: "I don't think nature really does sterile plants — it just takes the right conditions and almost anything can start setting seed. However, I would only recommend the dwarf series for people who are interested in the plant."

Buyer beware!

Doug Caldwell is landscape horticulture agent for the University of Florida, Collier County Cooperative Extension Service. For more information on home gardening, contact its Master Gardener Plant Clinic at 353-2872. For specimen identification, the clinic, at 14700 Immokalee Road, is open 9 a.m. to noon and 1 p.m. to 4 p.m. Monday, Wednesday and Friday; call 353-2872. Web site: collier.ifas.ufl.edu