Writer and physician Sir Thomas Browne (1605-82) was singularly unimpressed with certain human habits describing them as a “Trivial and vulgar way of coition,” regretting humans did not reproduce like trees. Little did he know about private lives of plants. Orgies such as those staged by the Roman Emperor Elagabalus pale to insignificance beside such horticultural happenings.
In all fairness to Sir Thomas, when he expressed his opinion in 1636 such was obscure. It was not until late in the same century and early in the next investigations by the German botanist and physician Rudolf Jacob Camerarius (1665-1721) commenced to reveal the secret sex life of plants. Then, as Susan Milius wrote recently in
Science News, “Despite these glorious shenanigans of blooms and birds and bees, plant sex is really plant-to-plant.”
Many trees, alas for Sir Thomas, are
dioecious: some bear only male flowers, others female ones. Their opposite numbers, species that are monoescious, have separate male and female flowers on the same tree. Then there are others that are hermaphrodite, which would doubtlessly have pleased Elagabalus no end.
Papaya ‘trees,’ which technically are not trees at all but like banana ‘trees’ enormous herbaceous plants, are usually dioecious. However, a few may grow as hermaphrodites although their fruit is usually somewhat puny. Confusing matters still further some papaya hermaphrodites choose later to revert to a dioecious state, raising no end of problems for their commercial growers in tropical climes.
In more temperate areas, home gardeners fancying a few blueberry bushes will find garden centres retail the shrubs in threes – two female to one male. Wise is the home horticulturalist that allows commercial nurseries to separate the sexes. It takes time to determine which is which. Holly (
Ilex) causes similar problems for those desiring the decorative berries.
Blueberry farmers are faced with a similar dilemma of sex in their bushes. A single male bush is all it takes to pollinate 20 females. Still, nature being nature, let to their own devices half those propagated will be female, half male. So most of the resulting male bushes are ‘rogued out,’ and destroyed, no doubt to the delight of feminists.
Not a few deciduous trees familiar to dwellers in northern climates are dioecious. Examples include willows, aspens, cottonwoods, mulberries, ashes and gingko. The last named can cause trouble.
Recently, residents in Japanese cities have been complaining about the odiferous fallen fruit from the vast numbers of gingko trees that line the streets. Local municipalities have been attempting to address the problem, the
Mainichi Daily News reported. The nuts contained within the flesh are part and parcel of Japan’s food culture. But the smell created by butyric acid in the crushed fruit has at best been compared with rancid butter, degrading into the odour of dog vomit – and worse. Gingko trees are valued for urban plantings thanks to their pest and pathogen resistance along with tolerance of urban conditions in many cities outside of Japan.
The answer to the odour is to plant only male trees. The same horticultural hijinks has solved the problem of ashes (
Fraxinus) dropping their winged seeds, or ‘keys,’ everywhere by, once again, only selecting male trees to adorn streets and gardens.
Sex is fun but involves much hard work. Worse yet, there may be no certain benefits. So why don’t all living things make like amoebas and simply split? Studying 32 species of
Oenothera, evening primrose, biologist Erika Hersch-Green and her colleagues compared half of these species that reproduce sexually with the other 16, which essentially clone themselves, reproducing asexually. The researchers reported in the
Journal of Evolutionary Biology that sexual reproduction strengthens an organism’s ability to adapt. Specifically, it may lead to stronger disease resistance. The Martian invaders in H. G. Well’s
War of the Worlds discovered to their cost that “budding’ reproductively is not the way to go.
Susan Milius is technically accurate: plant sex is plant-to-plant. But it certainly requires considerable assistance. Never mind the birds and the bees. Let’s not forget the bats that pollinate some cactus species or the slugs that, in the wild, are vital to the aspidistra’s satisfactory sex life. Others such as grasses and conifers rely on the wind to spread their fruitful promises to recipients near and far. This requires vast quantities of pollen to be released to the distress of asthma sufferers.
‘Birds do it, bees do it/Even educated fleas do it./Let’s do it, let’s fall in love, ” suggested lyricist Cole Porter (1954). Actually from certain plants’ viewpoint, ants may also help things along. This is may not always be a good idea. Found only on two adjacent cliff sides in the Pyrenees,
Borderea chouardi relies on two ant species as pollinators – and a third species to disperse the resulting seeds. Researchers writing in the open access journal PLoS One refer to this as a doubly mutualistic reproductive strategy and apparently not a very desirable one. The plant is critically endangered, thus truly a cliffhanger.
However, the romanticists among us will not be deterred. Valentine’s will be celebrated by an estimated 72 per cent of Canadians. Over half of men purchase flowers for the occasion. As Alfred, Lord Tennyson observed, “If I had a flower for every time I thought of you . . . I would walk through my garden forever.”
