Morphological differences and changes of the gynoecium in short-lived flowers of Rosa setigera Michaux and their relationship to dioecy

Rosa setigera is unique within the genus because the plant is cryptically dioecious, the flowers of male and female plants appearing identical. Flowers produce no nectar, and the plants rely upon insects, which feed on or collect pollen, for pollination. The plants' gynoecia in both sexes are extremely similar; however, overall the synstigmatic length, synstylar length, ovary length, ovule length, and ovule width are greater in flowers of female plants than in flowers of male plants. Only the single stigma width of male plants was found to be greater than that of female plants. Furthermore, ovary volume, ovary width, ovule length, ovule width, and ovule volume in flowers of female plants increase over the period of 4 d of a flower's life (i.e., with petals), whereas in flowers of male plants those characters either decrease or remain relatively constant over the 4-d time period. No overall differences in synstigmatic width, synstylar width, single stigma length, synstigmatic area, and ovary width were found. The results indicate that dioecy may be a relatively recent occurrence in this species.