Gender identity and the mystery of the persimmon fruit

Persimmon fruit

What does gender mean? We know that human gender is a broad and fluid landscape within which people choose to identify themselves. This is increasingly recognized as a healthy and welcoming way to think about who we are. Gender fluidity is true in many animal species, perhaps the majority.  But what about plants?

The photograph above is a mystery. Not its identity. It is a persimmon fruit lying on a driveway in Castlewood Park, Lexington. The mystery is the tree next to it. This is the only persimmon in the Park. I have known this tree for over 25 years and see it regularly, at least once a year. The mystery is that this is the only fruit this tree has ever produced, to my knowledge. And therein is the the tale of gender fluidity in a tree.

Persimmon, Diospyros virginiana, is a gorgeous tree with very distinctive bark. It is an important component of many forests from river bottoms to rocky hill slopes. In the Bluegrass, it is often found on farm hedgerows and the edge of woodlots. Persimmon is closely related to ebony (Diospyros ebenum and related species), the tree with dark brown or black wood famous for making the black keys on a piano, the pegs and fingerboard on violins, and fine clarinets.  The heartwood of persimmon is also very dark, but most trees have only a little heartwood with a much paler sapwood. Persimmon was prized for making golf clubs known as "woods", though today only a few artisans still make authentic persimmon clubs.

So why is this fruit so strange? As with humans, tree species often lie upon a spectrum of genders. This solitary fruit brings us to ask "what is the sex of this tree?"  Many trees are monoecious, with male and female reproductive organs in the same individual tree. Others are dioecious, with male trees and female trees. A large number of trees lie somewhere in the middle. Some trees are mostly male with a few female flowers. Others are the reverse. Botanists have made up dozens of words to describe various expressions of sex, such as polygamodioecious (mostly one sex, some flowers of another), subgynoecious (mostly female with a few male or bisexual flowers). Charles Darwin devoted much of his career to the forms of sexual expression in plants, writing three books on the subject and recognizing dozens of different patterns of sexual expression. 

For twenty five years, I have thought that this tree is male. Persimmon is one of the most strongly dioecious tree species in our flora. Trees are either male or female. Period. Yet here is a tree that has either been male the whole time I have known it, or has been asexual.  Scan as we might, my friend and I could not see another fruit in the tree or on the ground. Is this tree in transition from male to female, and will make more fruits in subsequent years?  Did one branch or one flower suddenly decide to be female for just a single occasion? We don't know, but this single fruit certainly compels us to keep an eye on the tree and await further developments. 

Gender identity in higher organisms is complicated, subject to evolutionary pressures that we barely understand. Gender identity in trees is complicated, difficult to understand, and fluid. Why should it be any different in humans? It shouldn't.

Persimmon tree
A persimmon, Diospyros virginiana, in Castlewood Park, Lexington

Stem of persimmon tree
Stem of persimmon tree in Castlewood Park