Regulation of gender and flowering behavior in a sexually dimorphic desert shrub (Ochradenus baccatus Delile [Resedacea])

The major goal of this study was to examine patterns of gender variation in Ochradenus baccatus, a shrub found in the Judean Desert and Arava Valley of Israel, whose breeding system was previously considered dioecious (separate male and female individuals). We conducted detailed measurements on 150 marked plants over two years to (1) quantitatively describe the variation in sex expression and elucidate the factors responsible for gender variation in males, (2) determine the role of plant size in regulating the flowering behavior through the year, and (3) document pollinator visitation to males and females. The variability in sex expression differed between males and females. Females only reproduced by seed. In contrast, gender in males was extremely variable: 35% of males reproduced only by pollen donation (pure males) and 65% produced pollen and varying amounts of fruit and seeds (inconstant males). The ability to produce fruit was highly correlated with individual plant size. Inconstant males were significantly larger than pure males. Individual plant size also determined the flowering pattern through the year. Unlike most other desert plant species that typically flower after the winter rains, large O. baccatus plants flowered all year. Small plants, regardless of sex, flowered only during the winter months. The flowers of O. baccatus were visited by a diverse suite of insects including wasps, bees, ants, beetles, flies, and butterflies. Perhaps owing to the greater attractiveness of the floral display of males (due to the presence of yellow pollen), males were visited by many more insects than females. Over four observation days, 526 insects were counted on male plants compared to only 39 on females.