Jack-in-the-Pulpit and Its Tricky Pollination Method


Jack-in-the-pulpits (Arisaema triphyllum) are native to much of the eastern two-thirds of the U.S. and grow in moist, rich woodlands. In Kentucky, they typically bloom in April and May. Their flowers aren’t very showy compared to some of our other spring wildflowers, but they have a unique shape. They also have some very interesting life history traits.

What we consider the Jack-in-the-pulpit’s flower is made up of a spathe and a spadix. The spathe makes up the “pulpit” which consists of the tube and overarching roof. It can be either green or a deep maroon color. The spadix is the part that pokes up out of the spathe and represents Jack. Either male or female flowers will be embedded in the spathe of most Jack-in-the-pulpits. A few Jack-in-the-pulpits will have both male and female flowers along the spathe, but only one type of flower will function. Jack-in-the-pulpits, therefore, are essentially either male or female.

Jack-in-the-pulpits are native wildflowers to much of the U.S. Photo credit: Joanna Gilkeson/USFWS 

One of the interesting life history traits of Jack-in-the-pulpits is that they can switch sex from one year to the next. Going back to basic botany, we know that flowering plants can either have male flowers, female flowers, or perfect flowers that contain both male and female parts. For many species that have male flowers on one plant and female flowers on another plant, any given plant will always be either male or female. However, that’s not true with Jack-in-the-pulpits. Young and small Jack-in-the-pulpits typically produce male flowers. Older, larger Jack-in-the-pulpits tend to produce female flowers. Also, if a female Jack-in-the-pulpit gets diseased, stressed, or otherwise doesn’t experience optimal growing conditions, then it may revert back to a male plant the next year.

The ability to switch sex from one year to the next isn’t the only interesting life history trait of Jack-in-the-pulpits. These woodland flowers also have an interesting pollination method. Jack-in-the-pulpit’s primary pollinators are fungus gnats. The larvae of fungus gnats feed on fungus, thus the name. The adults, on the other hand, are considered important pollinators of some plants. However, not all plants reward their pollinators with nectar.

When it comes to pollination, the Jack-in-the-pulpit has evolved a trick – instead of producing nectar, it produces an odor that smells like fungi. Since fungus gnats need to lay their eggs on fungus, the odor attracts them to the Jack-in-the-pulpit. The fungus gnat flies into the Jack-in-the-pulpit’s tube searching for the non-existent fungus. When the fungus gnat can’t find the fungus, it tries to fly out but the roof of the pulpit prevents it from doing so. Typically, the fungus gnat will hit the overarching part of the spathe and fall back into the tube.

For now, let’s pretend the fungus gnat is in a male Jack-in-the-pulpit. As the fungus gnat falls, it will bounce off the spadix and become dusted in pollen. It will keep trying to escape and keep tumbling back into the tube and getting dusted with more pollen as it bounces off the spadix again and again. The fungus gnat may also try to walk up the walls of the tube, but the inside of the tube is very smooth so the fungus gnat can’t get a good grip. In the process of trying to climb up the walls, the fungus gnat usually bounces off the spathe a few more times, causing it to get covered in even more pollen. Many male Jack-in-the-pulpits often have a pool of loose pollen sitting in the bottom of the tube so every time the fungus gnat falls to the bottom, it gets covered in, you guessed it, more pollen. Eventually, the fungus gnat will find the tiny hole that is located in the bottom of the tube of the male Jack-in-the-pulpit and will be able to escape.

By the time it escapes, the fungus gnat is thoroughly covered in pollen. The fungus gnat then flies off to find what it was looking for to begin with – a mushroom or other type of fungus. If instead it finds another male Jack-in-the-pulpit, then the whole process starts again. However, if the fungus gnat enters a female Jack-in-the-pulpit, then the story is slightly different.

Once again, the fungus gnat can’t easily escape because of the shape of the overarching roof and slick tube walls. And once again, the fungus gnat tumbles back into the tube multiple times and bounces off the spadix in the process. However, this time instead of the fungus gnat becoming dusted in pollen, the pollen on the fungus gnat is getting rubbed off onto the female flowers. The other part of the story that differs is that the female Jack-in-the-pulpits lack an exit hole. Once the fungus gnat enters a female Jack-in-the-pulpit, it is unlikely to escape.

Scientists hypothesize the lack of an exit hole in female Jack-in-the-pulpits evolved to ensure the fungus gnat spends as much time as possible in the tube, thus increasing the odds that the female flowers are pollinated. Female Jack-in-the-pulpit flowers that are pollenated will produce bright red berries along the spadix in late summer and early fall. Several species of birds will eat the berries.

As you walk through the woods this spring, I encourage you to keep an eye out for Jack-in-the-pulpits. They are a sign of a rich, moist forest ecosystem where many native, woodland plants can thrive. Also take a moment to contemplate the interesting life history traits of the Jack-in-the-pulpit. Rarely is anything as simple as it seems in nature and even uniquely shaped woodland flower can have complex stories waiting to be discovered.

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