Here’s a complex issue. Call it whatever you wish for the moment: Ruellia brittoniana, Ruellia malacosperma, Ruellia coerulea… given the available data, or rather lack thereof, I think colleagues Cecilia Ezcurra and Tom Daniel did a fine job of placing all these names into synonymy with the oldest available name for the taxon, Ruellia simplex Wright, in their 2007 Darwiniana paper. It may very well turn out that “Ruellia simplex” is composed of multiple species…. or not. But it is going to take some serious molecular data, and an intrepid graduate student.
Whatever the case may be, all these entities together form a species complex that is, to me, pretty distinctive, and can’t be confused with any other recognized species in the genus. This plant is cultivated for its attractive growth form and alluring flowers (see photo) but unfortunately, has become a noxious weed in some areas such as subtropical Florida. For several years, I have been working with horticulturist Rosanna Freyre at the University of Florida to attempt to understand what, if any, threats this species poses to the widely distributed native Ruellia caroliniensis.
Not vouchered, Mexico; Photo by Erin Tripp