Poster

         Development and Structure

Intrafloral Variation in Stamens and Staminodes in Mentzelia (Loasaceae)

Presenting Author
Jenna McClure
Description
Flowers evolve to optimize their reproductive output. Stamen, for example, should only be lost when the cost of building and maintaining them no longer benefits plant fitness. Staminodes, which are infertile stamen, no longer produce viable pollen but some have evolved a novel function that offers a different reproductive advantage. In Mentzelia section Bartonia (Loasaceae), petal-like staminodes have evolved repeatedly to increase the attractiveness of the flower to pollinators. Little is known, however, about whether staminodes evolve at the expense of stamens or in addition to stamens. Over half of the 51 species in Mentzelia section Bartonia have evolved at least one whorl of staminodes, and seven of those species have evolved multiple whorls. We hypothesized that flowers with staminodes would compensate for reduced male reproductive output by evolving additional whorls of fertile stamens. To determine how staminodes influence the number of stamens, we quantified androecial variation in flowers that had multiple whorls of staminodes. For some species, such as Mentzelia humilis, we found a negative relationship between staminodes and stamens—as the number of staminodes increased, the number of stamens decreased. Other species, such as Mentzelia collomiae and Mentzelia nuda, showed a consistent number of staminodes while the number of stamens varied within each species. We conclude that intrafloral variation in staminodes and stamens is dynamic across species—staminodes evolve at the expense of stamens in some flowers, but in others they evolve in addition to them.