Distyly in Polygonum jucundum Meisn. (Polygonaceae)

Distyly has been clearly confirmed in Polygonum jucundum Meisn. The distylous species is dimorphic for tepals, styles, stigmas, and pollen size and number. Long (L)-morph flowers are slightly larger than short (S)-morph flowers. The stigma width of thrum flowers is larger than that of pin flowers, and pin stigmas have longer and fewer papillae than the thrum ones. Flowers of the L-morph produced significantly smaller pollen grains in greater numbers than flowers of the S-morph. We found that Polygonum jucundum is not an obligate cross-pollination plant, and a reliable pollinator of the species is often available in the field. Our study revealed that flower flies are the most effective pollinators of Polygonum jucundum, whereas ants and thrips probably behave as “nectar thieves”; during the foraging process, however, thrips may effect pollination. In addition, other insects visited Polygonum jucundum flowers. The study supports the model proposed by Barrett that heterostyly is a strategy evolved to reduce sexual interference and inhibit self fertilization.