Hand-Pollination of Cardamine californica Improves Seed Set

Abstract

Hand-pollinating milkmaids (Cardamine californica (Nutt.) Greene var. integrifolia (Nutt.) Rollins [Brassicaceae]) increased seed set from 8% to 85%. In the Presidio of San Francisco, a district of the Golden Gate National Recreation Area in California, our restoration efforts using milkmaids were hampered by low seed set of our locally adapted plants. Plants in 2 populations were successfully cross-pollinated by hand and seeds ripened about 53 d later and were harvested. Although exact seed germination rates are not available, we noted that germination of hand-pollinated seeds was at least 40% in the nursery. This technique may be appropriate for other species in which natural reproduction is insufficient. We also discuss the role of natural pollinators and the physical changes that occur in the flowers during pollen maturation.