Nectar spurs have evolved in numerous families of flowering plants. In some genera, spurred flowers are simple structures involving a single perianth whorl (such as Linaria), whereas in other genera spurs are complex structures, involving both perianth and associated portions of the androecium and gynoecium (such as Delphinium). Heterotoma Zucc. was originally proposed for a large, red-flowered, Mexican, perennial lobelioid species that possesses a complex spur. Eleven small, blue-flowered, Mexican species of lobelias were added to the genus because they, too, possessed complex nectar spurs. In 1990, a monograph was published by Ayers that dismantled Heterotoma leaving only the type species, H. lobelioides. This realignment was based upon overall gross morphology, anatomical differences in the spurs, and evidence that one small, blue-flowered spurred species was sister to a non-spurred species in the genus Lobelia. A 1997 publication by Wilbur proposed recognition of the remaining 11 spurred species and one non-spurred species as a new genus, Calcaratolobelia. The current study was undertaken to test the taxonomic delimitations of the genera Lobelia and Heterotoma by gathering independent molecular data that might help resolve whether the Mexican spurred lobelioids should be treated as a distinct genus. Data from two independent molecular sources were gathered to address this question. We amplified the internal transcribed spacer (ITS) region and the matK gene from 10 species representing both genera. Preliminary evidence suggests that Heterotoma, as originally conceived, may be a good genus and that the presence of a nectar spur has more value than all other morphological characters. This study also suggests that morphological changes associated with humming bird pollination have evolved multiple times from blue-flowered, insect-pollinated relatives.

Key words: Heterotoma, ITS, Lobelia, matK, sytematics