The Complicated Sex Lives of Papayas

Female papaya tree with fruit

The St. Lucian workmen laughed when they saw our handsome papaya tree.
"That pawpaw is the wrong sex. You’ll never get any fruit from that one."

"How can you be sure what sex it is", I asked, thinking of all the effort we had put into growing it from a seed, planting it in the yard and nurturing it to maturity.

"No way to know until it grows up", they told me. "Then you can tell by the flowers." 

It seems the female flowers grow close to the stem of the plant, where the leaves are attached. The male flowers are smaller and thinner, and grow on stalks farther away from the stem. Sure enough, our papaya tree had flowers drooping far out from the stem.

"Nothing to do but chop it down. It’s no good" they said. Then one of the men suggested chopping off its head – the distinctive crown of leaves at the top of the stem.

"Maybe that will make it turn into a female."  Closer questioning produced more laughter and insinuations that maybe our papaya tree was an ‘anti-man’. Now I suspected they were just fooling with me. I had heard of fish changing sex under stressful environmental conditions, but not transsexual fruit.

The story got even more complicated when I looked up ‘papaya sex’ on the Internet. It seems that papayas come in three sexes: male, female and hermaphrodite. The male flowers produce pollen, but not fruit. The female plants have ovaries that can produce fruit, but their flowers need to be fertilized with pollen from another plant, otherwise the fruits won’t develop and will drop off while they are still small.

The third sex - hermaphrodite papaya trees - have flowers with ovaries as well as ones with pollen, so they can fertilize themselves without needing a partner - or even any help from the birds and the bees. Apparently papaya farmers prefer them because they are more dependable and produce the sweetest fruit. Their fruit is also longer than the fruit from a female papaya tree, which is rounder in shape. 

However, although hermaphrodite papaya trees have both male and female flowers, their yin and yang are not always exactly in balance. Some of the hermaphrodites have more male flowers and some have more female ones - and some flowers can actually change their sex. Warmer temperatures can make the hermaphrodite trees produce more male flowers, whereas cool temperatures or wet soil can make them have more female ones.

One article described efforts to do genetic testing on papayas to try to determine the sex of seedlings without having to wait for them to grow up. Commercial growers - or even backyard gardeners like me -  don’t want to waste their time and effort nurturing fruitless trees. Genetic mapping recently revealed that papayas have developed specialized sex chromosomes carrying genes that determine the sex of their offspring, remarkably like humans.  But it appears that sexual identity may not be all in the genes.

The female papaya trees were described as the most stable ones, with clearly defined sexuality.  Some seedlings, however, were identified as ‘sexually ambivalent males’.  It turns out that it is not just the hermaphrodite trees that are sexually unstable. Despite their sex chromosomes, male papaya trees can also end up changing their sexual orientation in response to seasonal changes and climate conditions.

And then I saw what I was looking for. Confirmation that the St. Lucians weren’t just pulling my leg. “Some male trees can be induced to change into female trees by decapitation.”  What an interesting manifestation of intelligent design. It may seem more like the French Revolution than the Garden of Eden, but sometimes heads just have to roll.   

Pearly-eyed thrasher eating papaya off the tree