Pinedrop (Pterospora andromedea)

Flowers: Mycotrophs

The day was hot and steamy as the sun rose above Flagstaff Trailhead in the Flatirons. The yarrow and Indian paintbrush were stretching their arms to the shade, aware of the heat wave of July. Yet underneath the canopy of ponderosas was a bright red plant with no need for the sun. It seemed content to sit there and smile, no matter what the temperature or radiating light. That plant is from a family known as Mycotrophic plants.

Most plants, as we learned in elementary school science, make their own food from sunlight, water, and carbon dioxide. They are green and are called autotrophs, meaning that they grow and are nourished through “self-feeding.” Their green color comes from the chlorophyll in the plant biology. However, there are other plants that are not green; having no chlorophyll, they cannot make their own food.

We learned that plants that grow without chlorophyll were called “saprophytes,” meaning that they derived their carbon and nutrients from decaying organic matter. Saprophytes were believed to grow in the shade below the canopy of big trees and survived on the dead leaves and branches in the understory. It turns out that those theories of non-chlorophyll survival were incorrect and today they are mostly rejected. Instead the relationships between many plant species and the soil fungi living in and around their root systems is more complex and nuanced. These plants are now called “heterotrophs,” meaning “other-feeding,” since they must obtain their nutrition from other organisms.

Heterotrophic plants, as the US Forest Service tells us, are divided into one of two groups, based upon how they get their food. The first of these groups are Parasitic plants. As parasites, they obtain their organic carbon from a host green plant directly through structures called haustoria. Wildflowers such as ground cone (Boshniakia strobilacea), California broomrape (Orobanche californica) and squawroot (Conopholis americana) possess no chlorophyll, all members of the broomrape family (Orobanchaceae), possess no chlorophyll and are examples of root parasites.[1]

The second of these groups are Mycotrophic plants (meaning they are “fungus feeding”). These plants obtain their organic carbon from a host green plant by tapping into an intermediary mycorrhizal fungus attached to the roots of the host plant. Many plant families include mycotrophs, especially in the tropics. In temperate North America, the orchid (Orchidaceae) and heath (Ericaceae) families include the highest numbers of mycotrophic genera. Coralroot orchids such as striped coralroot (Corallorhiza striata) and spring coralroot (Corallorhiza wisteriana), are included in but one of many orchid genera that are mycotrophs. All the members of the Monotropoideae subfamily of the heath family (Ericaceae) are mycotrophs such as these two plants: ghost plant (Monotropa uniflora) and sweet pinesap (Monotropsis odorata).

Many wildflower enthusiasts understand the symbiotic relationship between trees and mycorrhizal fungi. In this relationship, the hyphae (fungal threads) enter into the roots of the trees. The trees benefit by increasing the surface area of their root system allowing them to absorb greater quantities of water and minerals. In return, the fungus absorbs carbohydrates and other nutrients from the tree.

Since they cannot make their own “food,” the mysterious mycotrophic wildflowers take this symbiotic relationship between tree and fungus one-step further. Mycotrophic plants “tap” into and parasitize the hyphae of a mycorrhizal fungus by reversing the flow of carbon (derived from the host tree) and other nutrients to meet their survival needs. The unlucky fungus “feeds” the parasitic wildflower and receives nothing in return. Some people have even referred to this three-way relationship as “mutualism gone badly!” For this reason, the myco-heterotrophs are often said to be “epiparasitic” on other plants.

Several of the mycotrophic wildflowers are quite colorful and beautiful, such as the Snow Plant, Sugarstick, Pinedrop and Pinesap.

Snow plant (Sarcodes sanguinea) is a brilliant scarlet red. Sugarstick (Allotropa virgata) is another beautiful wildflower. This common name is derived from the beautiful red and white striping on the flower stalk. The wildflower in the Flatirons of Colorado is a pinedrop (Pterospora andromedea) and its cousin the pinesap (Monotropa hypopitys) are recognized with their shades of pinkish-red and yellow.

One of the more fascinating members of this group of mycotrophic wildflowers is the ghost plant (Monotropa uniflora). Ghost plant is a ghostly white translucent color.

[1]  https://www.fs.fed.us/wildflowers/beauty/mycotrophic/whatarethey.shtml