This species is among my top five favorite finds in the field. Prior to our covert operations to relocate it (a fieldtrip in which I was accompanied by Carrie Kiel and Kristen Hasenstab-Lehman), it had been collected only twice in history: first in the late 1800s (the type collection), and again in the early 1980s (when it was described under a different name). We found it in an amazing, high quality montane semi-deciduous forest just E of Chilpancingo. Unfortunately, access to this area was just recently made way, way, way too easy by construction of a brand new superhighway right through the gut of the region. I fear it is only a matter of time before the forests (and plants such as these) slowly disappear to make room for the strip malls…
Ruellia sororia is member to Ruellia section Chiropterophila, an entire clade of which, at present, is known only from Mexico. Species in section Chiropterophila are for the most part rare or extremely rare (see Tripp 2010, Systematic Botany). Ruellia sororia happens to be endemic to Guerrero. The plant is, among other reasons, remarkable for its morphological intermediacy between two morphological groups within sect. Chiropterophila. It is the only species in the clade that produces those strangely urceolate corollas AND produces flowers in dichasia.
Note the tinges of anthocyanin production in three visible whorls of the flower. This clade is otherwise marked by a complete lack of anthocyanin pigmentation.
Wild collected, Mexico, Tripp et al. 1206 (RSA-POM); Photo by Erin Tripp