Palm trees are more sexually fluid than once thought. Four individuals transitioning from male to female have been spotted in a Colombian forest.
Sexual expression is complicated in the plant world. Some plants are dioecious, meaning they are either male or female. Others are monoecious, so a single plant has male and female flowers. A third group is hermaphroditic, meaning their flowers have both male and female parts.
The Quind铆o wax palm () 鈥� Colombia鈥檚 national tree 鈥� was thought to be strictly dioecious. Flowers on male trees release pollen to fertilise flowers on female trees, which grow seeds that turn into red berry-shaped fruit.
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However, it seems this is not a hard-and-fast rule, says at Quind铆o Botanical Garden in Colombia.
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He and his colleagues surveyed more than 160 wild-growing C. quindiuense trees. All were clearly male or female, except for four males that were switching to female.
This is the first time palm trees have been documented changing sex, says Bernal.
The transitioning individuals had a mixture of new branches with female fruit and old, dead branches with shrivelled male flowers. The male branches were lower down and falling off, indicating they were from a past growth phase.
Longer-term data is needed to confirm that palm trees can fully transition from male to female, cautions at Rutgers University in New Brunswick, New Jersey. 鈥淚t is possible for a plant to do something one year that is out of the ordinary, without that constituting a change in sex.鈥�
Changing sex
have been documented in a small number of other dioecious plants, like and trees. No one knows why they do it.
Bernal says the palm trees鈥� location may offer a clue. The four transsexual trees were found close together in the Tochecito river basin in central Colombia. The site is unusual because it contains twice as many female as male聽C. quindiuense trees, instead of the typical equal sex ratio.
This regional trend towards femaleness may occur because the palm trees are at the lower limit of their preferred altitude range, says Bernal. Because females produce seeds, they are better at colonising new territories.
However, if anything stressed plants have a tendency to transition the other way, from female to male, says at the University of Lincoln, UK. This is because pollen-producing males require less energy and nutrients than fruit-bearing females. 鈥淧ollen is relatively cheap to produce compared to seeds.鈥�
Bernal鈥檚 team is now planning to study the transsexual palm trees in greater detail using drones. C. quindiuense is difficult to examine otherwise, because it is the tallest known palm tree, reaching over 25 metres.
Ecology
