Another Brooklyn blogger reports:
One crisis I've been tasked with dealing with [from a co-op board meeting] is one of our ginkgo trees in the front of our building has apparently decided to change its sex - from male to female; or at least one branch of it has done so.
- Thoughts While Looking Up, Ink Lake, 2009-11-17
Ginkgo biloba is a dioecious species, with male and female flowers on different plants (usually). The fruit of Ginkgos, which arise only from the flowers of female plants, is notoriously messy and smelly, hence the co-op's concern. We had a close encounter with some on the Sustainable Flatbush Street Tree Walking Tour a few weeks ago.
The gender of dioecious flowering plants can't be determined until they flower; male and female plants must be selected and copied through vegetative propagation techniques as cultivars, i.e.: clones. Hollies, Ilex, are also dioecious, and gardeners who want berries on their Hollies must purchase known-female cultivars and ensure that compatible males are close enough for pollination.
Flowers on the female cultivar of Ilex verticillata, Winterberry, in my backyard native plant garden. The sticky stigma, which receives the pollen from the flowers of the nearby male plant, is clearly visible in the center of the flower.
The ability of dioecious plants to change gender has been observed before, though it's unusual. The mechanisms by which individual plants "choose" their gender remains unknown; the accelerating capabilities of genetic technology are likely to change this. If any reader has some good references, please share them in a comment below.