The Sex Life of Trees

Despite the depictions of Hollywood and even more explicit viewing available through purveyors of pornography on the Internet, procreation among plants remains a mystery to many.

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Concerning the bees and the flowers In the fields and the gardens and the bowers, You will note at a glance That their ways of romance Haven’t any resemblance to ours.

A few years ago, we were assured by a new homeowner in Thornhill, north of Toronto, that the maple trees on her street were either male or female. Home handyman Harris Mitchell in his wonderful 1200 Household Hints You Wanted to Know (1983: Ancaster, Ontario) tells of a similar experience. “ I have a male and a female maple tree, which are growing close together,” his correspondent queried. “I would like to cut the female tree down to make room for a driveway, but understand the male tree will die if I do. Is this true?” Mitchell’s reply was that maple trees are bisexual. There could not be a male and a female. “Removing one will probably improve the other if they are growing close together,” he concluded, somewhat unsportingly. Horticultural, the hermaphrodite maples are monoescious. Other species, however, have chosen the dioecious way of life, with male and female flowers on separate trees. And not only trees either but many other samples of flora delight in separation of the sexes. Cannabis for example, as every grow-op operator knows, is normally dioecious. The male or staminate marijuana plant is a spindly and weaker grower compared with the opposite sex. The female or pistillate plant marijuana plant is what it’s all about. The active constituents that make Canadian cannabis so desirable to a certain portion of the population are found principally in the developing female flowers and adjacent leaves and stems. More familiar to many is the cottonwood (Populus deltoides) of our river valleys. Dioecious, during late spring the female trees produce seeds in a cottony mass. This is carried far and wide by the wind, perhaps kilometres away to coat city streets. Like its cousin aspen, the cottonwood has another trick up its sexual sleeve. It also spreads by cloning itself from root suckers. A thicket may thus comprise a single sex of genetically identical trees. In the same river valleys, where the soil is often rich, deep and moist, stinging nettles, Urtica dioica, invade. In summer these will bear small green catkins with male and female flowers on separate plants. Alas, like poison ivy, many a city type is unaware of the potential hazard. It is unwise to examine these sexual parts to closely, lest one becomes like the miserable miss from Mississippi:

There was a young lady in Natchez Who fell in some nettle-wood patches. She sits in her room With her little bare moon, And scratches, and scratches, and scratches.

All this is by no means a recent occurrence. Separate sexes of plants have been around for millions of years. As early as the dinosaurs, palm-like cycads were making out amidst the trampling, trumpeting Tyrannosaurus rex. While T. rex might have been big, a species of cycad has the largest sperm of any living organism. Like many other primitive plants such as ferns, the male cycad plant produces swimming sperm. The enormous cones these come from are distinctly suggestive in many species, enough to arouse the envy of Priapus, the Roman god of fertility. Humans have both helped and hindered dioecious plants. The sea buckthorn (Hippophae rhamnodies) is a small tree with bright silver foliage, tolerant of poor soil and wretched growing conditions in general. Late in the season the female trees are dense with masses of colourful fruit. Since this does not appeal to all gardeners, a Danish selection called ‘Sprite’ recently entered the market. All are male and therefore fruitless. On the other hand, hardy hollies are becoming ever more popular. In selling Ilex meserveae, many garden centres insist that, as in the song, ‘you can’t have one without the other.’ So a couple of I. meserveae ‘Blue Princess’ are accompanied by a single I. meserveae ‘Blue Prince’ to assure pollination and resultant berries. Yes, the polygamous prince enjoys multiple partners. Truth be told, a single male bush may be sufficient to take care of 20 or more females although it might be unwise to reveal this in front of avowed feminists, especially as another male holly rejoices in the highly suggestive name of ‘Blue Stallion.’ In fact, it is often no fun being a female tree. Take the marula tree (Sclerocarya birrea) of central and southern Africa for example. The tasty fruit a sought by elephants, to be spread far and wide. In doing so, the unfortunate female marula tree has her bark stripped off, branches torn away, and in general is badly battered by pachyderms pining for her produce. The fruit may also ferment somewhat, increasing its attractiveness to the elephants – and humans. Amarula, a creamy chocolate-tasting liqueur, is made from the fruit. Adding to the fun, some normally dioecious plants may, like oysters, choose to change sex. The late Berton Braley (1882-1966), valiant versifier, weighs in for the bivalve:

According to experts, the oyster In its shell – or crustacean cloister – May frequently be Either he or she Or both, if it should be its choice ter.

Some fruits also, as for example the delicious tropical papaya, Carica payaya, may decide in mid-career to cease to be male and become female or, to add to the fun, even hermaphrodite. Confusing things even further Carica, while it looks like a tree is, like the banana ‘tree,’ technically an herbaceous perennial. If all this arouses envy to the extent of perhaps even dressing up as a tree the better to woo in exotic fashion one’s true ladylove, consider the unfortunate experience of one such experimenter in the ways of wood:

There was a young man of Bengal Who went to a masquerade ball Arrayed like a tree, But he failed to foresee His abuse by the dogs in the hall.