1 - Yes, some trees may change sex after environmental stress.

Yard and Garden January 4, 2014

Q.

I read somewhere that trees can change sex. Is that true? It does not make sense. How can it happen?

A.

This is a complicated question. When I first heard about this, I was skeptical. While teaching a class of Master Gardeners experienced gardeners in the class mentioned several trees that had changed sex after an extremely severe winter. They described some male ginko trees in an open air courtyard area that changed from male to female following the severe winter. They had previously taken lunch breaks under these trees, but after the trees began producing very foul-smelling fruit, they could no longer eat lunch in that courtyard. Other gardeners described male ash trees beginning to produce to produce seed following excessive pruning. Some other gardeners went on to suggest that severe drought stress may have caused some seedless/fruitless (male) trees to begin producing seed. I have found mention of plants changing sex in scientific literate as well. It seems to be real!

As I thought more about this phenomenon, I began to consider how plants and animals are quite different. Most plants are monecious (male and female on one plant) while hermaphroditic animals are not as common (earthworms are examples of animal hermaphrodites). Since plants commonly have male and female flowers on the same plants and occasionally producing plants with flowers with only a single functional sex, it is not surprising that they can revert to a bisexual plant or even produce the other sex.

Mammals and many other animals have X and Y chromosomes. If the animal has two X chromosomes, then the animal will be female; if the animal has one X and one Y chromosomes, then the animal will be male. This was discovered in the early 1900s in mealworms. Mammals, including human beings, determine sex in this manner. Some other animals (many reptiles for example) do not have this type of sex determination; rather their sex is determined by environmental factors. So, it should not be surprising that plants can be likewise affected by their environment or stress conditions from the environment and management practices employed by gardeners.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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