Freeloading Plants

September 2015

by Linda Martinson 

Most plants are green because their leaves contain chlorophyll, a critical component of photosynthesis, a process used by plants to convert sunlight and carbon dioxide into chemical energy (stored as carbohydrates), and releasing oxygen as a waste product. Be grateful every day for photosynthesis, because it supplies all of the oxygen and most of the energy we need for life on Earth. However, about one percent of plants don’t have chlorophyll, so they are not green, they don’t photosynthesize, and they don’t need sunlight. They are freeloading plants, stealing their carbohydrates from other living organisms.

There are two basic categories of non-photosynthetic plants: 1) those that take their nutrition directly from another plant, and 2) those whose roots are connected to the mycelia (root-like threads) of a fungus which is connected to the roots of a living tree. The non-photosynthetic plants in this three-part energy swap with fungi and tree roots are myco-heterotrophic organisms, and two of them grow here at Richland Ridge and bloom from late summer through early fall.

More commonly seen is Indian pipe (Monotropa uniflora), associated with the Russala family of fungi, a member of the heath family along with mountain laurels and blueberries. Its flower stems push up from the shady forest floor in late summer/early autumn, usually in small clusters. The plant has a pipe shaped stem with scales (vestigial leaves) and a downturning flower. The entire plant is a ghostly, waxy white, and another common name for Indian pipe is corpse plant. The plants are fertilized by ground-nesting bees, and each flower produces hundreds of dust-like seeds. Only a few of these seeds germinate, however, because they thrive only in deep, shady forests with rich, loamy, and undisturbed soil with the proper fungi.

Indian pipe (Monotropa uniflora). Credit: Linda Martinson

Less commonly seen is Pine sap (Monotropa hypopithys), a close relative of Indian pipe. The two plants look somewhat alike, but each stem of Pine sap supports a cluster of nodding flowers instead of just one. Its blooming season is a little longer and later than Indian pipe, and the plants tend to turn color as it gets cooler, to a bright pink or red. Although the name indicates an association with pine trees, Pine sap does not have to be near pine trees to grow. 

Pine sap (Monotropa hypopithys) Credit: Linda Martinson

Finally, there is a third freeloading plant here at Richland Ridge that takes its nutrition directly from a host plant instead of using an intermediary fungus: American squawroot (Conopholis americana), also known as bear corn or cancer-root. Squawroot, however, blooms in the early spring rather than in late summer/early fall. Unlike the seedlings of photosynthesizing plants, when a squawroot seed germinates, it forces its way underground until finds the root of an oak or beech tree to invade. A colony of flowering stalks that resemble pine cones emerges in the spring, and are readily pollinated by several insects even though they have no scent. The plant doesn’t seem to cause any severe or lasting damage to the tree roots. The lore is that bears eat squawroot as a laxative when they come out of hibernation explaining the common name, bear corn.

Squawroot (Conopholis americana)

The relationship of myco-heterotrophic plants with fungi has only recently been explored and explained. For many years, it was believed that plants like Indian pipe and Pine sap were saprophytes, i.e., drawing their nutrition from dead and decaying organic material. And even more recent is the discovery of the role of fungi in plant communication. It is exciting to think of how much more there is to learn about the vast underground world of plants and fungi.