Jack-in-the-Pulpit, Arisaema triphyllum

Jack-in-the-Pulpit

Jack-in-the-pulpit is usually found in moist deciduous woodlands, especially in the rich soils of the river bottomlands. This well-known plant is a symbol for many people of the woods in late spring.

Each plant produces one or two three-part leaves with long stalks; a separate stalk bears the jack-in-the-pulpit itself (the flower and the enclosing sheath). The flowers are usually found in May or June; they bloom later than most of the other forest wildflowers, coming out about the same time as the leaves on the trees open.

The jack-in-the-pulpit belongs to the Arum family. The flowers are similar to those of the other members of the family such as the skunk cabbage, wild calla, or sweet flag. The numerous small individual flowers are borne on a fleshy spike, the spadix. This flower-bearing spadix is surrounded by a modified leaf that partially wraps around and encloses the spadix in a tube and forms a hood over it. This is the pulpit, or, more technically, the spathe. Formerly it was thought that there were three species of jack-in-the-pulpit in our area; now these are treated as varieties of a single species. The species is very distinctive and we all consider that we "know it." However, if we look at it more closely it reminds us just how fascinating and wonderful other forms of life are.

Spadix and Spathe Mature Berries
flower bearing spadix and enclosing spathe mature berries in fall

Pollen from male plants is carried to female plants by tiny fungus gnats, a small insect related to flies. The fungus gnats are probably attracted to the jack-in-the-pulpits by something about its smell, which may, to them, resemble the fungi on which they normally lay their eggs. The gnats are not adapted to gather or carry pollen the way honeybees are, but transfer pollen accidentally if it clings to their bodies. The gnats fly into the pulpit and are then unable to fly back up and out of the narrow tube or to climb its slick walls. As they try, however, they come in contact with the flowers and in a male flower may pick up pollen. In the male plants the spathe that wraps around the spadix to form the pulpit doesn't quite meet at the base and thus leaves a small exit hole. Fungus gnats that go to a male plant eventually do get out, perhaps bearing with them a few pollen grains. In the female plants the spathe has no exit hole and the fungus gnats are trapped to thrash around indefinitely. As they do they may transmit pollen from a previous visit to a male plant to the waiting female flowers. For all its apparent sophistication, it is actually not a very efficient scheme as usually only a few flowers are fertilized on each female plant.

When fertilization has occurred the female flower is transformed during the summer into a berry containing from one to a few seeds. The berries on the spadix enlarge and burst out of the old pulpit. In the late summer, as they mature, they turn bright red. In the fall the leaves of the plant die back and starches created during the summer are stored in the underground corm for next year's plant.

Jack-in-the-Pulpit

Jack-in-the-pulpits grow slowly in the dark shaded understory of the forest. A small young plant may accumulate only enough energy during the course of the summer to put forth another set of leaves next year. After a few years the plant may accumulate enough stored energy to produce a flower. The first year the plant flowers, the flower is usually a male. Male flowers use up only a moderate amount of energy, as they are only temporary structures designed to produce pollen. They do not cause much of a drain on the plant's energy.

After several seasons of producing male flowers the plant will get larger and can then produce a spadix with a mixture of male and female flowers. The female flowers and the resulting berries that grow throughout the summer cost the plant a great deal in terms of energy. Only with a large store of energy from the previous year can the plant afford to produce the female flowers. Finally, after more years of accumulation on energy, the plant may produce a spadix that contains only female flowers.

In this species natural selection has favored delaying the female phase of life until the plant is large enough and has enough accumulated energy to support the production of the seed-containing berries. It requires many years to reach this stage and a plant may be twenty years old before it produces only female flowers. In undisturbed sites the average life of a plant may be about 100 years.

This sequence is not inviolate. In a very good site, the intermediate combined male and female spadix may be skipped. On the other hand, in a very poor site (very wet or dry, low light intensity, low pH) the plant may never progress beyond the male only or the male plus female spadix.

Also, the sex change is reversible. A female plant which has had a bad year because it was trampled or eaten by slugs may not have enough energy stored at the end of the growing season to support a female flower next year. It may therefore produce only a male flower or perhaps no flower at all. This process is again reversible, so that after a few good years the plant may again produce female flowers.

This plasticity allows the plants to adapt to changes in their environment. They need not be locked in on a particular response that they may not have the resources to support. Each plant optimizes its chance to contribute to the next generation of jack-in-the-pulpits by making a developmental decision about what kind of flower to produce next year. The actual decision seems to be based on the amount of starch stored by the end of the summer.


 

Plants Boquet River