Reproductive biology of Eryngium yuccifolium (Apiaceae), a prairie species

Temporal dioecism is a synchronized flowering sequence with minimal overlap between the pistillate and staminate phases of an individual plant. This strategy allows pollen to be shed before stigmas become receptive, minimizing geitonogamous pollinations and maximizing outcrossing. I studied this condition using Eryngium yuccifolium Michx., a tallgrass prairie perennial species. As a temporaly dioecious species, E. yuccifolium exhibits the following characteristics: 1) an extended pistillate phase, with stigmas becoming receptive only after the anthers have shed pollen and dehisced, 2) synchronized flower heads, 3) numerous flower heads visited by generalist pollinators, and 4) some degree of self-compatibility as indicated by hand pollinations. Finally, results from open and bagged pollinations and high pollen-ovule ratios indicated that the species is xenogamous. This study also found high fruit and seed sets (close to 90%) for E. yuccifolium. However, intense herbivory by the larva of a Gelechiidae moth significantly reduced the reproductive output of the species by destroying 40-60% of flowers and fruits. The results of this study indicate that temporal dioecism can enhance outcrossing and potentially can explain the high fruit and seed set for E. yuccifolium.