Trees’ gender swapping mystifies, fascinates scientists
It’s not often a scientist reaches into fantasy literature for the perfect analogy.
“Usually trees take a long time to respond to their environment,” said botanist Jennifer Blake-Mahmud. “Remember the Ents in Lord of the Rings? It takes them a long time to say anything in Entish!”
Some things – or people or Ents – just don’t want to rush it. Most trees don’t rush anything, especially when it comes time to bloom. A lot of trees have some type of flower, which contains their sexual organs. The showier plants, like cherry, magnolia and dogwood, flaunt their sexuality. But for many trees, you can barely notice or see their blossoms. All this blossoming usually takes months to fully develop, sometimes as long as 11 months, but it’s usually set in motion during the winter for their spring appearance.
Only when the trees bloom can you figure out their sex. Lots of trees are hermaphro- ditic – that is, their flowers contain both male and female reproductive parts. Other species have male trees and female trees, which you can tell apart by looking at their flowers: The male reproductive parts are the pollen-laden stamen; the female parts their egg-holding pistils.
Acer pensylvanicum, a striped maple found in the northeast United States and southeastern Canada, is that rarest of species: Not only can it take a mere three weeks to bloom (a nanosecond in arboreal terms), but an individual tree can switch genders, from male to female. Blake-Mahmud announced the discovery, along with Lena Struwe, in the journal Trees: Structure and Function.
Why they switch genders, of course, is of abiding interest of Blake-Mahmud, a PhD student at Rutgers University and an expert in plant reproduction. It all started six years ago when she attended a field course on the biology of sex at the Mountain Lake Biological Station in Virginia.
“We were traipsing through the forest and encountered the [striped maple],” Blake-Mahmud remembered. “They said they think it changes sex but are not sure why. I was like: ‘Wow, what’s going on? This sounds crazy.’”
“Crazy” turned into a recent series of laboratory experiments at Rutgers. Mahmud and her team cut branches from striped maples in various forested regions of New Jersey, then nurtured them in a greenhouse until the branches bloomed.