Posted by Cathy Scott on April 28, 2016
Epiparasites the Freddie the Freeloader of Plants
Do you have friend(s) that always shows up for the potluck empty-handed, or they surprise you by showing up for dinner unannounced? You keep them around because they are fun, and their devil-may-care attitude can distract you from the rigors of life. There are actually plants like that too. Captivating plants like Squawroot, Dutchman's Pipe here in the east, and out west, Snow Plant.
These plants evolved to live without making their own chloroplyll. Chlorophyll is the molecule that allows plants to gather energy from the sun and to make all the yummy things we love to eat. Why would the Freddies of the plant world give up the ability to make it’s own food? Why do the work when you can get the food for free.
For a long time these plant were thought to be saprophytes. That is, organisms that feed off of dead and decaying matter in a similar manner as mushrooms and other fungi. This was mostly because studies showed that Freddie did not interact directly with other plants (via roots connections), like most parasites. The truth is more complicated. Turns out they do take energy from plants but through an intermediary—Fungus! (Leake 2004)
All plants have evolved symbiotic relationships with fungi. The fungus breaks up humus and other matter in the soil and provide minerals in a usable form for the plants. Their abundant surface structure of fine mycelium allows for more efficient uptake and transfer of water than roots alone. In return, the plants provide sugars for the fungus (Sanders 2003).
Freddie plants evolved knowing they can get the all the sugars and minerals he needs to survive from the other plants and fungi. Their only job is to make the next generation and move on. They know this gig is temporary. The environmental cues for each species are well coordinated, all come up at once. Flowers at the ready to make the next generation of freeloaders. They do their thing, seed and die back to the ground. No need for leaves to stick around to harness the suns energy for later days.
A few of the scientific papers I looked at described these plants as “cheaters”. I found that a little harsh. I can’t dislike these plants for their freeloading ways. These little natural anomalies are like artists, they awaken the spirit. Just like the smooth saxaphone meanderings of the jazz song, "Freddie the Freeloader", or those friends that show up every now and then. Coming across little white pipes in the woods or Squawroot in bloom or its ghostly remnants, always bring me joy.
Leake, J. R. (2004). "Myco-heterotroph/epiparasitic plant interactions with ectomycorrhizal and arbuscular mycorrhizal fungi." Current Opinion in Plant Biology 7(4): 422-428.
More than 400 achlorophyllous plant species in 87 genera are parasitic upon fungi, and exploit them as their principle source of carbon. With a few exceptions, most of these myco-heterotrophic plants are now thought to be 'cheats', stealing carbon and nutrients from the mycorrhizal associates of adjacent autotrophic plants. Most myco-heterotrophs are therefore considered to be epiparasitic on green plants. Both the ectomycorrhizal and arbuscular mycorrhizal symbioses have been invaded by myco-heterotrophic epiparasites. DNA analysis is revealing the identities of many of the fungal partners of myco-heterotrophs, and their exceptionally high specificity. Myco-heterotrophs have distinctive stable isotope signatures, which can be used to establish the dependence upon fungal carbon of green plants that are partially myco-heterotrophic.
Sanders, I. R. (2003). "Preference, specificity and cheating in the arbuscular mycorrhizal symbiosis." Trends in Plant Science 8(4): 143-145.
Arbuscular mycorrhizal symbioses are mutualistic interactions between fungi and most plants. There is considerable interest in this symbiosis because of the strong nutritional benefits conferred to plants and its influence on plant diversity. Until recently, the symbiosis was assumed to be unspecific. However, two studies have now revealed that although it can be largely unspecific with the fungal community composition changing seasonally, in certain ecosystems it can also be highly specific and might potentially allow plants to cheat the arbuscular mycorrhizal network that connects plants below ground.