A Plant Called Pipsissewa

Pipsissewa flowers are pollinated by bumblebees in summer. (Bob Armstrong | For the Juneau Empire)

The rapidly lengthening days of March are an annual pleasure for us all, I think. They also make some of us fidgety — eager for spring and summer to arrive. As I write this, however, the early morning temperatures at my house are around five degree Fahrenheit, which suggests that I might be a be over-eager with my fidgeting.

 

Nevertheless, my thoughts turned to a small shrubby plant in the forest understory, one that blooms in summer. So I decided to write about it, even though it is not exactly seasonally appropriate.

This little plant is called pipsissewa (or sometimes prince’s pine, though it has nothing to do with either princes or pines); it scientific name is Chimaphila umbellata. A friend called to my attention a small patch of it one summer day, as we prowled along the lower slopes on the west side of Mendenhall Lake. Later, I realized that a lot of this plant grows along the road near the upper powerhouse on the Salmon Creek road, and we have since seen it in several other spots.

Then it dawned on me that I knew absolutely nothing about this plant except that it belongs to the wintergreen family and, like its relatives, pipsissewa has shiny evergreen leaves. So I dug up some information. This species grows in the mountain west and across the boreal forests of North America and Eurasia, and research information comes from eastern North America and northern Europe.

When summer finally rolls around again, pipsissewa produces a few pinkish-white flowers, more or less saucer-shaped. The flowers are said to have a faint aroma, and they produce nectar. Pipsissewa flowers later in the summer, after many other species have finished flowering. It is pollinated primarily by nectar-collecting bumblebees. Many of the pollinating bees are males, which are produced late in the season. Although they are less efficient pollinators than the (female) worker bees, they gain a source of energy for flying around looking for females with which to mate (those queens will produce next year’s broods of workers). The flowers are self-compatible, meaning that pollen originating on a given individual can fertilize ovules and produce seeds on the same plant. But it usually takes a bee to accomplish the pollen transfer from the anthers, where pollen is produced, to the female-receptive parts of the flower. Pollen grains are produced in clumps of many grains stuck together, so many of the seeds that develop from each pollination event are likely to be full-siblings with the same father.

Pipsissewa produces large amounts of very tiny seeds that hold little nutrition for a developing seedling (as is true for other wintergreens and for orchids). The seeds are buoyant and disperse on vagrant puffs of air in the understory, but most seeds probably don’t go very far. One study found that germination was better if seeds landed near an established adult plant and in more acid soils.

The miniscule size of the dust-like seeds means that some other source of seedling nutrition is needed, since so little is stored in the seed itself. Pipsissewa and other plants with dust-like seeds are ‘fed’ via fungal connections to other plants that are well-established, already photosynthesizing carbohydrates, which the fungi transport to pipsissewa and other plants; these fungi also supply nitrogen and other nutrients to the growing seedling. As the young pipsissewa grows to adulthood, it apparently becomes less dependent on the fungal connections for carbohydrates but still obtains other nutrients that way.

The fungal connections are called mycorrhizae (fungus-root), which have featured in my essays many times. Most plants, including ferns and mosses, in our forests have these connections, moving nutrition from plant to plant. Some plants are entirely dependent on their mycorrhizae for growth and maintenance, others are only partly or temporarily dependent, while still others are much less dependent and may serve chiefly as suppliers. I suspect that we would not recognize our familiar forests if they lacked these fungal connections; altogether, one could say that fungi make our forest what they are!


• Mary F. Willson is a retired professor of ecology.


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