Jack, Jill, Then Jack Again

The Unconventional Sex Life of a Plant

The Jack in the pulpit (Arisaema triphyllum) is one of my favorite flowers and a harbinger of spring when I lived in the northeast. When I say flower, I use the term loosely, because the actual flowers are inconspicuous. What’s dramatically visible is the fleshy spike—called a spadix (Jack)-- on which the small flowers are born, and the colorful bract (a modified leaf), called a spathe (the pulpit), which completely surrounds the spadix, even providing a roof of sorts. The spathes are what first catches your eye; in my area they were shades of purple, sometimes of a dark hue close to black. (For wonderful images of these flowers, look on the internet for the series of paintings by Georgia O’Keeffe, from her early years, when she vacationed at Lake George, N.Y.)

These are singular plants, in the context of the northeast forests where I observed them, seemingly escapees from a tropical conservatory. Relatives include popular houseplants such as philodendron, dieffenbachia and monstera. But Jack in the pulpits (henceforth, JPs), are distinctive as well for their sex lives. The vast majority of seed-bearing plants are both male and female, that is, hermaphrodites. There are two types of hermaphroditic plants, those that produce flowers or cones with both male and female parts, and those that produce separate male and female flowers/cones but on the same plant. Only a minority, about 10% of plant species, have separate male and female individuals. JP is one such species, as is American holly, mulberry, cannabis and gingko, to name a few with which you might be familiar, for one reason or another. The Gingko (Gingko biloba) is worth an aside.

(The gingko is the sole survivor of an ancient lineage of the sort often referred to as living fossils. Native to East Asia where it is almost extinct in the wild, it has long been imported to the rest of the northern hemisphere as an ornamental tree and planted in many public spaces. Gingkoes grow slow but live long (up to 1,000 years) and eventually attain massive size. Originally both sexes were imported, as you would expect. But many municipalities banned the import of female gingkoes because they prolifically produce fleshy fruit-like structures about the size of a table grape. Unfortunately, the fruits smell like vomit mixed with dog shit, especially when squashed by human or auto traffic. So if you see a Gingko less than 100 years old, it’s likely to be a male.

But in places like New York City, where some of the first gingkoes were imported, you can still find plenty of old female gingkoes. In parts of Brooklyn, they abound. The dropped “fruits” of these old broad-canopied trees can cover a large swath of ground, which it is best to avoid, lest they jelly on the bottom of your shoes with a sticky stinky ooze. When I first noticed elderly Asian women wading into the fallen “fruit”, collecting the malodorous things, I was flummoxed. I knew Asians weren’t as squeamish as those of us of European decent, but this seemed to be pushing the envelope. So I did some internet research and discovered that for Koreans and Chinese alike, the fetid flesh was just an inconvenience. They were after the seed inside, which they roasted. These seeds are said to have a flavor of pinenuts. It’s backbreaking labor, so they must have an attractive taste indeed.)

JPs have male and female plants but with a twist. Jack can become Jill or vice versa. Moreover, they can change their sex from year to year. JPs are perennials but they die back each winter and become dormant until spring. When they emerge, they rely on nutrients stored in a swollen underground stem called a corm. The size of the corm depends on the age of the plant and the amount of nutrients acquired during the previous growing season. Younger plants have smaller corms on average than older plants. And plants of whatever age that had a good growing season grow larger corms than those that didn’t.

The corm size also predicts whether the JP will be male or female the following year. Big corms tend to generate female flowers, small corms promote male development. This makes sense when you consider that being a female JP is more energetically taxing than being a male. It is the females that produce the beautiful berries after the flower dies. After a year as a female the JP may have depleted most of the nutrients stored in the corm. If so, Jill will be Jack the next spring. Then, after a year as Jack, its corm reloaded, Jill will reemerge next season.

This is quite a fete. Not surprisingly, it is quite rare; only a few other plant species, including the striped maple, can pull if off. This sort of sex switching is beyond the capacities of any animal species, even fishes. Or is it?

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